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DAY 3 — C Programming Part 1 — Complete Study Material

Phase 1: Technical Theory | Date: 23 July 2026 | Subject: C Programming Basics | Expected Questions: 6–7

📌 Day Overview

Today you will study:

Basic structure of a C program
Tokens, keywords, identifiers, and comments
Data types: char, int, float, and double
Variables and constants
The sizeof operator
Input and output basics
Arithmetic, relational, logical, bitwise, assignment, increment, decrement, and ternary operators
Operator precedence and associativity
if, if-else, nested if, else-if ladder, and switch
for, while, and do-while loops
break and continue
Output-tracing techniques

Five-Hour Study Plan

Hour	Topic
1	C basics, data types, variables, constants, and sizeof
2	Operators
3	Precedence, associativity, and output tracing
4	Decision statements
5	Loops, break, continue, and output tracing

1. C Basics, Data Types, Variables, Constants, and sizeof

1.1 What Is C?

C is a general-purpose programming language.

It was developed by Dennis Ritchie at Bell Laboratories in the early 1970s.

C is widely used for:

Operating systems
Compilers
Embedded systems
Device drivers
Database software
Networking software
System utilities

Why Is C Important?

C provides:

High-level programming features
Low-level memory access
Fast execution
Portability
A small set of keywords
Structured programming

Middle-Level Language

C is often called a middle-level language because it supports:

High-level features such as functions and loops
Low-level features such as pointers, bitwise operations, and direct memory access

This is a textbook description, not an official language category.

1.2 Compiler and Source Code

A C program is written as source code.

A C compiler translates the source code into a form the computer can execute.

C Source Program
       │
       v
   Preprocessor
       │
       v
    Compiler
       │
       v
    Assembler
       │
       v
   Object Code
       │
       v
     Linker
       │
       v
Executable Program

Source File Extension

A C source file commonly uses the extension:

.c

Example:

program.c

1.3 Basic Structure of a C Program

A simple C program is:

#include <stdio.h>

int main(void)
{
    printf("Hello");
    return 0;
}

Line-by-Line Meaning

Preprocessor Directive

#include <stdio.h>

This includes declarations from the standard input/output header.

stdio means standard input/output.
.h means header file.
printf and scanf are declared in stdio.h.

main Function

int main(void)

Execution of a hosted C program begins with the main function.

int means main returns an integer.
void inside the parentheses means that this form of main accepts no parameters.

Opening and Closing Braces

{
}

Braces create a block of statements.

printf

printf("Hello");

printf displays formatted output.

Semicolon

A semicolon normally ends a C statement.

return

return 0;

Returning 0 from main indicates successful program termination.

1.4 C Is Case-Sensitive

C treats uppercase and lowercase letters as different.

These identifiers are different:

age
Age
AGE

These keywords are not the same:

int
INT

Only lowercase int is a C keyword.

1.5 C Tokens

A token is the smallest meaningful unit of a C program.

Main token categories are:

Keywords
Identifiers
Constants
String literals
Operators
Punctuators

Example

int total = 25;

Tokens are:

int
total
=
25
;

1.6 Keywords

A keyword is a reserved word with a predefined meaning in C.

Examples:

Keyword	Purpose
int	Integer type
char	Character type
float	Floating-point type
double	Higher-precision floating-point type
if	Decision statement
else	Alternative decision
switch	Multi-way selection
case	Case label
for	Loop
while	Loop
do	Loop
break	Terminates loop or switch
continue	Skips to next loop iteration
return	Returns from a function
void	Indicates no value or no parameters in specific contexts
const	Makes an object non-modifiable through that name
sizeof	Gives size in bytes

A keyword cannot normally be used as a variable name.

Invalid:

int for = 10;

1.7 Identifiers

An identifier is a name given to a program element.

Examples:

Variable name
Function name
Array name
Structure name

Valid Identifier Rules

An identifier:

Can contain letters, digits, and underscore.
Must not begin with a digit.
Must not contain spaces.
Must not contain symbols such as @, #, %, or -.
Must not be a C keyword.
Is case-sensitive.

Examples

Identifier	Valid?	Reason
total	Yes	Contains letters
total_marks	Yes	Underscore is allowed
marks2	Yes	Digit is not first
_count	Yes	May begin with underscore, though some underscore names are reserved
2marks	No	Begins with a digit
total marks	No	Contains a space
total-marks	No	Contains a hyphen
float	No	It is a keyword

Good Naming Style

Use meaningful names:

totalMarks
student_count
average

Avoid unclear names:

x1
aaa
qqq

Short names such as i and j are commonly used as loop counters.

1.8 Comments

Comments are notes for programmers. They are ignored during normal program execution.

Single-Line Comment

// This is a single-line comment

Single-line comments are supported in C99 and later.

Multi-Line Comment

/* This is
   a multi-line comment */

Important Point

Traditional C comments cannot be nested safely.

Invalid idea:

/* Outer comment /* Inner comment */ */

1.9 Data Types

A data type tells the compiler:

What kind of value is stored
How the value is interpreted
What operations are allowed
How much memory is required

Main Basic Data Types

Data Type	Main Use	Example
char	Character or small integer	'A'
int	Integer	25
float	Single-precision floating-point value	3.14f
double	Double-precision floating-point value	3.14
void	Absence of a value	Function returning nothing

1.10 char Data Type

The char type stores a character code or a small integer.

Example:

char grade = 'A';

A character constant uses single quotation marks:

'A'
'7'
'@'

char and Integer Codes

Characters are stored internally as numeric codes.

In ASCII:

'A' = 65
'a' = 97
'0' = 48

Example:

char ch = 'A';
printf("%d", ch);

Output on an ASCII-based system:

Guaranteed Size

In C:

sizeof(char) = 1

This is always one C byte.

A C byte contains at least 8 bits. On most modern systems, one byte is 8 bits.

char Variants

char
signed char
unsigned char

A plain char may behave as signed or unsigned depending on the implementation.

1.11 int Data Type

The int type stores whole numbers.

Examples:

int age = 20;
int temperature = -5;
int total = 1000;

It does not store a fractional part.

Integer Type Modifiers

signed
unsigned
short
long
long long

Examples:

short int a;
unsigned int b;
long int c;
long long int d;

These shorter forms are also valid:

short a;
unsigned b;
long c;
long long d;

1.12 Signed and Unsigned Integers

A signed integer can represent:

Negative numbers
Zero
Positive numbers

An unsigned integer represents:

Zero
Positive numbers

For an unsigned n-bit integer:

Range = 0 to 2ⁿ − 1

Example for 8 bits:

0 to 2⁸ − 1
= 0 to 255

For a typical n-bit two’s-complement signed integer:

Range = −2ⁿ⁻¹ to 2ⁿ⁻¹ − 1

Example for 8 bits:

−128 to 127

1.13 float Data Type

The float type stores real numbers with fractional parts.

Example:

float price = 12.5f;

The suffix f makes 12.5f a float constant.

Without f, a decimal floating constant such as 12.5 has type double.

Typical Precision

A float commonly provides about 6–7 significant decimal digits.

Example:

float x = 3.1415926f;

1.14 double Data Type

The double type stores floating-point values with greater precision than float.

Example:

double distance = 12345.6789;

Typical Precision

A double commonly provides about 15–16 significant decimal digits.

long double

long double provides at least as much precision as double.

Example:

long double value = 3.14L;

The suffix L indicates a long double constant.

1.15 void Data Type

void means the absence of a value in specific contexts.

Function Returning No Value

void showMessage(void)
{
    printf("Hello");
}

No Function Parameters

int main(void)

Here, void means the function accepts no parameters.

sizeof(void)

Standard C does not define sizeof(void). Some compilers accept it as an extension, but it should not be used in standard C.

1.16 Sizes of C Data Types

Important Accuracy Rule

The C language does not fix one exact byte size for every data type.

The exact size can depend on:

Compiler
Processor
Operating system
Data model

The only exact basic rule here is:

sizeof(char) = 1

The following relationships are guaranteed:

sizeof(char) ≤ sizeof(short)
sizeof(short) ≤ sizeof(int)
sizeof(int) ≤ sizeof(long)
sizeof(long) ≤ sizeof(long long)

Common Sizes on Modern Systems

Type	Common Size	Typical Purpose
char	1 byte	Character or small integer
short	2 bytes	Small integer
int	4 bytes	General integer
long	4 or 8 bytes	Larger integer
long long	8 bytes	Large integer
float	4 bytes	Single-precision real number
double	8 bytes	Double-precision real number
long double	8, 12, or 16 bytes	Extended precision

Common Competitive-Exam Table

Many basic examinations expect:

Data Type	Commonly Expected Size
char	1 byte
short int	2 bytes
int	4 bytes
long int	4 or 8 bytes
long long int	8 bytes
float	4 bytes
double	8 bytes
long double	Implementation-dependent

If a question names a compiler or architecture, use the sizes for that environment.

1.17 Minimum Ranges Required by C

Type	Minimum Required Range
signed char	−127 to 127
unsigned char	0 to 255
short	−32767 to 32767
unsigned short	0 to 65535
int	At least −32767 to 32767
unsigned int	At least 0 to 65535
long	At least −2147483647 to 2147483647
unsigned long	At least 0 to 4294967295
long long	At least −9223372036854775807 to 9223372036854775807

Modern two’s-complement systems commonly include the additional most-negative value, such as −128 for 8-bit signed char.

1.18 The sizeof Operator

The sizeof operator returns the size of a type or object in bytes.

Syntax

sizeof(type)

or:

sizeof expression

Examples

sizeof(char)
sizeof(int)
sizeof(double)

int x;
sizeof(x)

Example Program

#include <stdio.h>

int main(void)
{
    printf("%zu", sizeof(int));
    return 0;
}

%zu is the correct printf format specifier for the result of sizeof.

Important Rules

sizeof(char) is always 1.
sizeof returns an unsigned integer type called size_t.
Parentheses are required when a type name is used.
Parentheses are usually optional for an ordinary expression.
sizeof does not usually evaluate its operand.

Example:

int x = 5;
printf("%zu %d", sizeof(x++), x);

For an ordinary non-variable-length object, x++ is not executed inside sizeof.

Typical output when int is 4 bytes:

4 5

sizeof an Array

int a[10];

sizeof(a)

If int is 4 bytes:

sizeof(a) = 10 × 4 = 40 bytes

Within the same scope where a is an actual array:

Number of elements = sizeof(a) / sizeof(a[0])

1.19 Variables

A variable is a named memory location whose stored value can change.

Declaration

int age;

This tells the compiler that age is an integer variable.

Initialization

int age = 20;

Initialization gives the variable its first value when it is created.

Assignment

age = 25;

Assignment changes its value.

Multiple Variables

int a, b, c;

Multiple Initializations

int a = 10, b = 20, c = 30;

1.20 Local Variables and Initialization

A local automatic variable that is not initialized has an indeterminate value.

Example:

int main(void)
{
    int x;
    printf("%d", x);
}

This program has undefined behaviour because x is read without initialization.

Always initialize variables before reading them.

Correct:

int x = 0;

1.21 Constants

A constant is a fixed value that does not change during program execution.

Integer Constants

Examples:

10
-25
1000

Integer Bases in C

Form	Example	Meaning
Decimal	25	Decimal 25
Octal	031	Decimal 25
Hexadecimal	0x19	Decimal 25

Important Point

An integer literal beginning with 0 is traditionally interpreted as octal.

010 = decimal 8

019 is invalid as an octal integer because 9 is not an octal digit.

Floating Constants

Examples:

3.14
-0.25
6.02e23
1.5f
2.0L

Scientific notation:

6.02e23 = 6.02 × 10²³

Suffixes:

f or F: float
l or L: long double

Character Constants

A character constant uses single quotes:

'A'
'7'
'\n'

A character constant represents an integer character code.

String Literals

A string literal uses double quotes:

"Hello"
"A"
"123"

Character vs String

Character Constant	String Literal
'A'	"A"
Single quotes	Double quotes
Represents one character code	Represents a sequence ending with a null character

Escape Sequences

An escape sequence represents a special character.

Escape Sequence	Meaning
\n	New line
\t	Horizontal tab
\b	Backspace
\r	Carriage return
\	Backslash
'	Single quotation mark
"	Double quotation mark
\0	Null character

Example:

printf("A\nB");

Output:

A
B

Symbolic Constants with const

const int MAX = 100;

MAX should not later be assigned another value through that name.

Invalid:

MAX = 200;

Symbolic Constants with #define

#define PI 3.14159

The preprocessor replaces PI with 3.14159 before compilation.

const vs #define

const	#define
Declares a typed object	Creates a preprocessor macro
Processed by compiler	Processed before compilation
Obeys scope rules	Macro scope follows preprocessing rules
Has a data type	Simple replacement has no C data type by itself

1.22 Basic Input and Output

printf

printf displays formatted output.

printf("Hello");

Format Specifiers

Data Type	printf Format
int	%d or %i
unsigned int	%u
long int	%ld
long long int	%lld
char	%c
float expression	%f
double	%f
long double	%Lf
String	%s
Hexadecimal integer	%x or %X
Octal integer	%o
sizeof result	%zu

Example

int age = 20;
printf("%d", age);

Output:

scanf

scanf reads formatted input.

int age;
scanf("%d", &age);

The & operator gives the address of age.

Common scanf Formats

Data Type	scanf Format
int	%d
char	%c
float	%f
double	%lf
long double	%Lf

Important:

printf uses %f for a double argument.
scanf uses %f for float and %lf for double.

1.23 Type Conversion

Type conversion changes a value from one data type to another.

Implicit Conversion

The compiler performs it automatically.

int x = 5;
double y = x;

x is converted to double.

Explicit Conversion

The programmer requests conversion using a cast.

double result = (double)5 / 2;

Without the cast:

5 / 2 = 2

With the cast:

(double)5 / 2 = 2.5

Type Cast Syntax

(target_type) expression

Example:

(float)a
(int)x

2. Operators

An operator is a symbol that performs an operation on one or more operands.

Example:

a + b

- is the operator.
a and b are operands.

2.2 Arithmetic Operators

Operator	Operation	Example
+	Addition	a + b
-	Subtraction	a - b
*	Multiplication	a * b
/	Division	a / b
%	Remainder	a % b

Integer Division

When both operands are integers, the result is an integer.

The fractional part is discarded toward zero.

7 / 2 = 3
9 / 4 = 2
-7 / 2 = -3

To get a floating-point result:

7.0 / 2 = 3.5

or:

(double)7 / 2 = 3.5

Remainder Operator

The % operator returns the remainder after integer division.

7 % 2 = 1
10 % 3 = 1
15 % 5 = 0

The operands of % must have integer types.

Invalid:

5.5 % 2.0

Common Use: Even or Odd

if (number % 2 == 0)
    printf("Even");
else
    printf("Odd");

Division by Zero

Division or remainder by integer zero is undefined.

Invalid:

10 / 0
10 % 0

2.3 Unary Plus and Minus

Unary operators work on one operand.

int a = 5;
int b = -a;

Now b is −5.

Examples:

+a
-a

2.4 Relational Operators

Relational operators compare values.

Operator	Meaning
<	Less than
>	Greater than
<=	Less than or equal to
>=	Greater than or equal to
==	Equal to
!=	Not equal to

In C:

True relational result is 1.
False relational result is 0.

Examples:

5 > 3   gives 1
5 < 3   gives 0
5 == 5  gives 1
5 != 5  gives 0

Assignment vs Equality

=   assignment
==  equality comparison

Example:

x = 5;

stores 5 in x.

x == 5

checks whether x equals 5.

2.5 Logical Operators

Logical operators combine or reverse conditions.

Operator	Meaning
&&	Logical AND
\|\|	Logical OR
!	Logical NOT

In C:

Zero is false.
Any non-zero value is true.
Logical results are 0 or 1.

Logical AND

A && B is true only when both operands are true.

A	B	A && B
0	0	0
0	1	0
1	0	0
1	1	1

Example:

(5 > 2) && (8 > 3)
= 1 && 1
= 1

Logical OR

A || B is true when at least one operand is true.

A	B	A \|\| B
0	0	0
0	1	1
1	0	1
1	1	1

Logical NOT

! reverses the logical value.

!0 = 1
!1 = 0
!25 = 0

Short-Circuit Evaluation

Logical AND

For:

A && B

If A is false, B is not evaluated.

Example:

int x = 0;
int y = 0 && ++x;

x remains 0.

Logical OR

For:

A || B

If A is true, B is not evaluated.

Example:

int x = 0;
int y = 1 || ++x;

x remains 0.

2.6 Bitwise Operators

Bitwise operators work on individual bits of integer operands.

Operator	Meaning
&	Bitwise AND
\|	Bitwise OR
^	Bitwise XOR
~	Bitwise complement
<<	Left shift
>>	Right shift

Do not confuse:

Logical	Bitwise
&&	&
\|\|	\|
Works with truth values	Works on individual bits

Bitwise AND

A result bit is 1 only when both input bits are 1.

A	B	A & B
0	0	0
0	1	0
1	0	0
1	1	1

Example:

Therefore:

12 & 10 = 8

Bitwise OR

A result bit is 1 when at least one input bit is 1.

Therefore:

12 | 10 = 14

Bitwise XOR

XOR produces 1 when the bits are different.

A	B	A ^ B
0	0	0
0	1	1
1	0	1
1	1	0

Example:

Therefore:

12 ^ 10 = 6

XOR Properties

x ^ 0 = x
x ^ x = 0

Bitwise Complement

~ changes every bit:

0 becomes 1.
1 becomes 0.

On a common two’s-complement system:

~x = −x − 1

Example:

~5 = −6

The exact visible bit pattern depends on the integer width.

Left Shift

x << n

Shifts bits n positions to the left.

For a non-negative value when the result is representable:

x << n is equivalent to x × 2ⁿ

Example:

Therefore:

5 << 1 = 10

Right Shift

x >> n

Shifts bits n positions to the right.

For non-negative integers:

x >> n is equivalent to integer division by 2ⁿ

Example:

20 >> 2

20 / 4 = 5

Therefore:

20 >> 2 = 5

Avoid relying on right-shift details for negative signed integers in basic output questions because the result is implementation-defined.

2.7 Assignment Operators

Simple Assignment

x = 10;

The right-side value is stored in the left-side object.

Assignment associates from right to left.

a = b = 5;

This works as:

a = (b = 5);

Both a and b become 5.

Compound Assignment

Operator	Meaning
+=	Add and assign
-=	Subtract and assign
*=	Multiply and assign
/=	Divide and assign
%=	Remainder and assign
&=	Bitwise AND and assign
\|=	Bitwise OR and assign
^=	Bitwise XOR and assign
<<=	Left shift and assign
>>=	Right shift and assign

Examples:

x += 3;

means approximately:

x = x + 3;

If x is 5, it becomes 8.

2.8 Increment and Decrement

Increment

The ++ operator increases a variable by 1.

x++;

or:

++x;

Decrement

The -- operator decreases a variable by 1.

x--;

or:

--x;

Prefix Increment

++x

The value is increased before the expression uses it.

Example:

int x = 5;
int y = ++x;

Result:

x = 6
y = 6

Postfix Increment

x++

The old value is used first, and then x is increased.

Example:

int x = 5;
int y = x++;

Result:

y = 5
x = 6

Prefix Decrement

int x = 5;
int y = --x;

Result:

x = 4
y = 4

Postfix Decrement

int x = 5;
int y = x--;

Result:

y = 5
x = 4

Unsafe Increment Expressions

Do not try to predict expressions that modify the same variable multiple times without proper sequencing.

Examples to avoid:

i = i++ + ++i;
printf("%d %d", i++, i);
a[i] = i++;

Such expressions may have undefined behaviour. They do not have one reliable output.

Use separate statements:

int old = i;
i++;
printf("%d %d", old, i);

2.9 Conditional or Ternary Operator

The conditional operator uses three operands.

Syntax

condition ? expression_if_true : expression_if_false

Example

int max = (a > b) ? a : b;

If a is greater than b, max receives a. Otherwise, max receives b.

Example

int x = 10;
printf("%s", (x % 2 == 0) ? "Even" : "Odd");

Output:

Even

It is called the ternary operator because it uses three operands.

2.10 The Comma Operator

The comma operator evaluates expressions from left to right and produces the value of the last expression.

Example:

int x;
x = (2, 4, 6);

x becomes:

Do not confuse the comma operator with commas used to separate function arguments or declarations.

3. Operator Precedence and Associativity

3.1 What Is Precedence?

Precedence decides which operator binds more strongly when an expression contains different operators.

Example:

2 + 3 * 4

Multiplication has higher precedence:

2 + (3 * 4)
= 2 + 12
= 14

Not:

(2 + 3) * 4 = 20

3.2 What Is Associativity?

Associativity decides the grouping direction when operators have the same precedence.

Left-to-Right Example

Multiplication and division have the same precedence and associate left to right:

24 / 6 * 2
= (24 / 6) * 2
= 4 * 2
= 8

Right-to-Left Example

Assignment associates right to left:

a = b = 10

Grouping:

a = (b = 10)

3.3 C Operator Precedence Table

The table goes from highest precedence to lowest.

Level	Operators	Meaning	Associativity
1	() [] . -> postfix ++ postfix --	Postfix operations	Left to right
2	prefix ++ prefix -- + - ! ~ (type) * & sizeof	Unary operations	Right to left
3	* / %	Multiplication, division, remainder	Left to right
4	+ -	Addition, subtraction	Left to right
5	<< >>	Bit shifts	Left to right
6	< <= > >=	Relational	Left to right
7	== !=	Equality	Left to right
8	&	Bitwise AND	Left to right
9	^	Bitwise XOR	Left to right
10	\|	Bitwise OR	Left to right
11	&&	Logical AND	Left to right
12	\|\|	Logical OR	Left to right
13	?:	Conditional	Right to left
14	= += -= *= /= %= &= ^= \|= <<= >>=	Assignment	Right to left
15	,	Comma	Left to right

3.4 Precedence Memory Order

Memorize this practical order:

Parentheses
Postfix increment/decrement
Unary operators
Multiplication, division, remainder
Addition, subtraction
Shifts
Relational
Equality
Bitwise AND
Bitwise XOR
Bitwise OR
Logical AND
Logical OR
Ternary
Assignment
Comma

3.5 Important Expression Examples

Example 1

5 + 2 * 3

= 5 + 6
= 11

Example 2

(5 + 2) * 3

= 7 * 3
= 21

Example 3

20 / 5 * 2

Same precedence, left to right:

= (20 / 5) * 2
= 4 * 2
= 8

Example 4

10 - 4 - 2

Left to right:

= (10 - 4) - 2
= 6 - 2
= 4

Example 5

5 > 3 && 2 < 4

Relational operators are evaluated before logical AND:

= 1 && 1
= 1

Example 6

5 == 5 || 3 > 8

= 1 || 0
= 1

Example 7

4 + 2 << 1

Addition has higher precedence than shift:

= (4 + 2) << 1
= 6 << 1
= 12

Example 8

10 & 6 == 2

Equality has higher precedence than bitwise AND:

= 10 & (6 == 2)
= 10 & 0
= 0

Use parentheses when the intended grouping could be unclear:

(10 & 6) == 2

10 & 6 = 2
2 == 2 = 1

3.6 Best Rule for Real Programs

Do not depend on memory alone for complicated expressions.

Use parentheses:

result = (a + b) * c;

Parentheses improve:

Correctness
Readability
Maintenance
Output tracing

4. Decision and Control Statements

A control statement changes the normal order in which statements execute.

Decision statements include:

if
if-else
nested if
else-if ladder
switch

4.1 Simple if Statement

Syntax

if (condition)
{
    statement;
}

If the condition is non-zero, the block runs.

If the condition is zero, the block is skipped.

Example

int age = 20;

if (age >= 18)
{
    printf("Adult");
}

Output:

Adult

4.2 Truth in C

C treats:

0 as false
Any non-zero value as true

Example:

if (5)
    printf("Yes");

Output:

Yes

Example:

if (0)
    printf("Yes");

No output is produced.

4.3 if-else Statement

Syntax

if (condition)
{
    statements_if_true;
}
else
{
    statements_if_false;
}

Example

int number = 7;

if (number % 2 == 0)
    printf("Even");
else
    printf("Odd");

Output:

Odd

4.4 Braces and Single Statements

If an if or else controls only one statement, braces are optional.

if (x > 0)
    printf("Positive");

For multiple statements, use braces:

if (x > 0)
{
    printf("Positive");
    x++;
}

Recommended practice: use braces even for one statement.

4.5 Common Braces Error

if (x > 0)
    printf("Positive");
    printf("Checked");

Only the first printf belongs to the if statement.

The second printf runs regardless of the condition.

Correct:

if (x > 0)
{
    printf("Positive");
    printf("Checked");
}

4.6 Nested if

A nested if is an if statement inside another if statement.

Example

int x = 15;

if (x > 0)
{
    if (x % 2 == 0)
        printf("Positive even");
    else
        printf("Positive odd");
}
else
{
    printf("Not positive");
}

Output:

Positive odd

4.7 Dangling else Rule

An else is matched with the nearest unmatched if.

Example:

if (a > 0)
    if (b > 0)
        printf("Both positive");
    else
        printf("b is not positive");

The else belongs to:

if (b > 0)

Use braces to make the intended structure clear.

4.8 else-if Ladder

Use an else-if ladder when testing several conditions in order.

Syntax

if (condition1)
{
    statements1;
}
else if (condition2)
{
    statements2;
}
else if (condition3)
{
    statements3;
}
else
{
    default_statements;
}

Example

int marks = 75;

if (marks >= 90)
    printf("A");
else if (marks >= 75)
    printf("B");
else if (marks >= 60)
    printf("C");
else
    printf("D");

Output:

Important Point

Only the first true branch runs.

Order matters.

Incorrect order:

if (marks >= 40)
    printf("Pass");
else if (marks >= 75)
    printf("Distinction");

A mark of 80 satisfies marks >= 40 first, so the second test is never reached.

4.9 switch Statement

A switch selects one path using the value of an integer, character, or enumeration expression.

Syntax

switch (expression)
{
    case constant1:
        statements;
        break;

    case constant2:
        statements;
        break;

    default:
        statements;
}

Example

int day = 2;

switch (day)
{
    case 1:
        printf("Monday");
        break;

    case 2:
        printf("Tuesday");
        break;

    case 3:
        printf("Wednesday");
        break;

    default:
        printf("Invalid");
}

Output:

Tuesday

4.10 switch Rules

The switch expression must have an integer, character, or enumeration type.
case labels must be constant integral expressions.
Duplicate case values are not allowed.
default is optional.
break is optional.
The order of case labels does not determine matching.
Only one default label is allowed in one switch.
Character constants can be used as case values.

Example:

switch (grade)
{
    case 'A':
        printf("Excellent");
        break;

    case 'B':
        printf("Good");
        break;
}

4.11 Fall-Through in switch

Without break, execution continues into later cases.

Example:

int x = 2;

switch (x)
{
    case 1:
        printf("A");

    case 2:
        printf("B");

    case 3:
        printf("C");
        break;

    default:
        printf("D");
}

Output:

BC

Execution begins at case 2 and continues through case 3 until break.

4.12 Grouping Cases

Several cases can share one block.

switch (ch)
{
    case 'a':
    case 'e':
    case 'i':
    case 'o':
    case 'u':
        printf("Vowel");
        break;

    default:
        printf("Not a lowercase vowel");
}

4.13 if-else vs switch

if-else	switch
Supports ranges and complex conditions	Compares one expression with constant case values
Can use relational and logical expressions	Uses equality-like matching
Suitable for few or complex choices	Suitable for many fixed choices
Can test floating-point conditions	switch expression cannot have floating type
No automatic fall-through	Fall-through occurs without break

5. Loops

A loop repeats a block of statements.

C provides:

for loop
while loop
do-while loop

5.1 Loop Components

Most loops contain:

Initialization
Condition
Body
Update

Example:

int i = 1;

while (i <= 5)
{
    printf("%d ", i);
    i++;
}

Initialization: i = 1
Condition: i <= 5
Body: printf
Update: i++

5.2 while Loop

The while loop tests the condition before executing the body.

Syntax

initialization;

while (condition)
{
    statements;
    update;
}

Example

int i = 1;

while (i <= 5)
{
    printf("%d ", i);
    i++;
}

Output:

1 2 3 4 5

Entry-Controlled Loop

while is an entry-controlled loop because it checks the condition before entering the body.

It may execute zero times.

Example:

int i = 10;

while (i < 5)
{
    printf("%d", i);
}

The body does not run.

5.3 do-while Loop

The do-while loop executes the body first and tests the condition afterward.

Syntax

initialization;

do
{
    statements;
    update;
}
while (condition);

Important Point

A semicolon is required after the while condition.

Example

int i = 1;

do
{
    printf("%d ", i);
    i++;
}
while (i <= 5);

Output:

1 2 3 4 5

Exit-Controlled Loop

do-while is an exit-controlled loop.

Its body executes at least once.

Example:

int i = 10;

do
{
    printf("%d", i);
}
while (i < 5);

Output:

5.4 for Loop

A for loop places initialization, condition, and update in one line.

Syntax

for (initialization; condition; update)
{
    statements;
}

Example

int i;

for (i = 1; i <= 5; i++)
{
    printf("%d ", i);
}

Output:

1 2 3 4 5

Execution Order

Initialization
     │
     v
  Condition ─── false ───> Exit
     │
    true
     │
     v
    Body
     │
     v
   Update
     │
     └────────────> Condition

Initialization runs once.

Condition is checked before every iteration.

Update runs after each completed iteration.

5.5 for Loop Variations

Counting Down

for (i = 5; i >= 1; i--)
    printf("%d ", i);

Output:

5 4 3 2 1

Update by Two

for (i = 0; i <= 10; i += 2)
    printf("%d ", i);

Output:

0 2 4 6 8 10

Multiple Expressions

for (i = 0, j = 5; i < j; i++, j--)
{
    printf("%d %d\n", i, j);
}

Missing Sections

Each of the three sections can be omitted.

for (;;)
{
    statements;
}

This creates an infinite loop unless something such as break terminates it.

5.6 while vs do-while vs for

Feature	for	while	do-while
Condition checked	Before body	Before body	After body
Minimum executions	0	0	1
Type	Entry-controlled	Entry-controlled	Exit-controlled
Best use	Known or structured repetition	Condition-based repetition	Body must run at least once
Semicolon after condition	No	No	Yes

5.7 Nested Loops

A loop inside another loop is a nested loop.

Example

int i, j;

for (i = 1; i <= 2; i++)
{
    for (j = 1; j <= 3; j++)
    {
        printf("*");
    }

    printf("\n");
}

Output:

***
***

Iteration Count

If the outer loop runs m times and the inner loop runs n times for each outer iteration:

Total inner executions = m × n

Example:

Outer loop = 3 times
Inner loop = 4 times

Total = 3 × 4 = 12

5.8 Infinite Loops

An infinite loop does not terminate naturally.

Examples:

while (1)
{
}

for (;;)
{
}

Accidental infinite loop:

int i = 1;

while (i <= 5)
{
    printf("%d", i);
}

i never changes, so the condition remains true.

5.9 break Statement

break immediately terminates the nearest enclosing:

for loop
while loop
do-while loop
switch statement

Example

int i;

for (i = 1; i <= 10; i++)
{
    if (i == 5)
        break;

    printf("%d ", i);
}

Output:

1 2 3 4

When i becomes 5, break ends the loop.

Nested Loop Rule

break exits only the nearest enclosing loop.

for (i = 1; i <= 2; i++)
{
    for (j = 1; j <= 5; j++)
    {
        if (j == 3)
            break;

        printf("%d ", j);
    }
}

The outer loop continues.

5.10 continue Statement

continue skips the rest of the current iteration and moves to the next iteration.

for Loop Example

int i;

for (i = 1; i <= 5; i++)
{
    if (i == 3)
        continue;

    printf("%d ", i);
}

Output:

1 2 4 5

while Loop Care

In a while loop, update the loop variable before continue if required.

Correct:

int i = 0;

while (i < 5)
{
    i++;

    if (i == 3)
        continue;

    printf("%d ", i);
}

Output:

1 2 4 5

5.11 break vs continue

break	continue
Terminates the loop completely	Skips only the current iteration
Control moves after the loop	Control moves to the next iteration
Also used in switch	Not used to exit switch
Nearest enclosing loop or switch	Nearest enclosing loop

Mnemonic:

break = break out
continue = continue with next iteration

5.12 Common Loop Patterns

Sum of 1 to n

int i;
int sum = 0;

for (i = 1; i <= n; i++)
{
    sum += i;
}

For n = 5:

sum = 1 + 2 + 3 + 4 + 5 = 15

Factorial

The factorial of n is:

n! = n × (n − 1) × ... × 2 × 1

Example:

5! = 5 × 4 × 3 × 2 × 1 = 120

Program pattern:

int i;
int fact = 1;

for (i = 1; i <= n; i++)
{
    fact *= i;
}

Count Digits

int count = 0;

while (n != 0)
{
    n /= 10;
    count++;
}

For n = 538:

538 → 53 → 5 → 0

Count:

Reverse Digits

int reverse = 0;

while (n != 0)
{
    int digit = n % 10;
    reverse = reverse * 10 + digit;
    n /= 10;
}

For n = 123:

reverse = 321

5.13 Output-Tracing Method

Use this process for every output question:

Write the initial value of each variable.
Add parentheses according to precedence.
Follow prefix and postfix rules.
Check integer division.
Check whether a condition is 0 or non-zero.
For loops, create an iteration table.
Track break and continue.
Check switch fall-through.
Reject undefined-behaviour questions instead of inventing an output.

Loop Trace Table Example

For:

int i;
int sum = 0;

for (i = 1; i <= 3; i++)
    sum += i;

Iteration	i	sum before	sum after
1	1	0	1
2	2	1	3
3	3	3	6

Final sum:

🔑 Quick Revision Sheet

Basic C Structure

#include <stdio.h>

int main(void)
{
    statements;
    return 0;
}

Common Data Types

Type	Common Size	Use
char	1 byte	Character/small integer
short	2 bytes	Small integer
int	4 bytes	Integer
long	4 or 8 bytes	Larger integer
long long	8 bytes	Large integer
float	4 bytes	Single-precision real
double	8 bytes	Double-precision real

Only this is universally exact:

sizeof(char) = 1

Other exact sizes depend on the implementation.

Format Specifiers

Type	printf	scanf
int	%d	%d
unsigned int	%u	%u
char	%c	%c
float	%f	%f
double	%f	%lf
long int	%ld	%ld
long long int	%lld	%lld
long double	%Lf	%Lf
sizeof result	%zu	—

Operator Rules

Arithmetic

+  -  *  /  %

Relational

<  <=  >  >=  ==  !=

Logical

&&  ||  !

Bitwise

&  |  ^  ~  <<  >>

Assignment

=  +=  -=  *=  /=  %=

Increment and Decrement

++x  x++  --x  x--

Ternary

condition ? true_value : false_value

Practical Precedence Order

Parentheses and postfix
Unary
Multiplication, division, remainder
Addition and subtraction
Shifts
Relational
Equality
Bitwise AND
Bitwise XOR
Bitwise OR
Logical AND
Logical OR
Ternary
Assignment
Comma

Control Statements

Statement	Use
if	One conditional path
if-else	Two paths
else-if ladder	Multiple conditions
nested if	Decision inside a decision
switch	Fixed constant choices

Loop Comparison

Loop	Condition	Minimum Execution
for	Before body	0
while	Before body	0
do-while	After body	1

break and continue

break terminates the loop or switch.
continue skips the remaining statements in the current loop iteration.
break in a nested loop exits only the nearest loop.
continue does not terminate the complete loop.

📝 Practice Questions

Theory Questions: 1–10

Question 1

Who developed the C programming language?

A. James Gosling
B. Dennis Ritchie
C. Bjarne Stroustrup
D. Guido van Rossum

Question 2

Which is a valid C identifier?

A. 2marks
B. total-marks
C. total_marks
D. float

Question 3

Which statement is guaranteed by standard C?

A. sizeof(int) is always 2
B. sizeof(int) is always 4
C. sizeof(char) is always 1
D. sizeof(double) is always 8

Question 4

Which format specifier is used with printf for a value returned by sizeof?

A. %d
B. %f
C. %zu
D. %c

Question 5

Which operator tests equality?

A. =
B. ==
C. !=
D. <=

Question 6

Which operator performs bitwise XOR?

A. &&
B. ||
C. ^
D. ~

Question 7

Which operator has higher precedence?

A. Addition over multiplication
B. Logical OR over logical AND
C. Multiplication over addition
D. Assignment over equality

Question 8

Which loop always executes its body at least once?

A. for
B. while
C. do-while
D. None of these

Question 9

Which statement immediately terminates the nearest enclosing loop?

A. continue
B. break
C. case
D. sizeof

Question 10

Which statement about switch is correct?

A. Its expression must always be a float.
B. Duplicate case values are permitted.
C. break prevents fall-through to later cases.
D. default is compulsory.

Operator and Expression Output Questions: 11–20

Assume stdio.h is included and each fragment is placed correctly inside main.

Question 11

What is the output?

printf("%d", 2 + 3 * 4);

A. 14
B. 20
C. 24
D. 11

Question 12

What is the output?

printf("%d", (2 + 3) * 4);

A. 14
B. 18
C. 20
D. 24

Question 13

What is the output?

int x = 7 / 2;
printf("%d", x);

A. 3
B. 3.5
C. 4
D. 2

Question 14

What is the output?

printf("%.1f", 7.0 / 2);

A. 3.0
B. 3.5
C. 4.0
D. 7.0

Question 15

What is the output?

printf("%d", 17 % 5);

A. 2
B. 3
C. 4
D. 5

Question 16

What is the output?

int x = 5;
int y = x++;
printf("%d %d", x, y);

A. 5 5
B. 5 6
C. 6 5
D. 6 6

Question 17

What is the output?

int x = 5;
int y = ++x;
printf("%d %d", x, y);

A. 5 5
B. 5 6
C. 6 5
D. 6 6

Question 18

What is the output?

printf("%d", (5 > 3) && (2 < 1));

A. 0
B. 1
C. 2
D. 5

Question 19

What is the output?

printf("%d %d %d", 12 & 10, 12 | 10, 12 ^ 10);

A. 8 14 6
B. 14 8 6
C. 8 6 14
D. 6 14 8

Question 20

What is the output?

int x = 0;
int y = 0 && ++x;
printf("%d %d", x, y);

A. 0 0
B. 1 0
C. 1 1
D. 0 1

Control Statements and Loop Output Questions: 21–30

Question 21

What is the output?

int x = 7;

if (x % 2 == 0)
    printf("Even");
else
    printf("Odd");

A. Even
B. Odd
C. 7
D. No output

Question 22

What is the output?

int marks = 80;

if (marks >= 90)
    printf("A");
else if (marks >= 75)
    printf("B");
else if (marks >= 60)
    printf("C");
else
    printf("D");

A. A
B. B
C. C
D. D

Question 23

What is the output?

int x = 2;

switch (x)
{
    case 1:
        printf("A");

    case 2:
        printf("B");

    case 3:
        printf("C");
        break;

    default:
        printf("D");
}

A. A
B. B
C. BC
D. BCD

Question 24

What is the output?

int i;

for (i = 1; i <= 5; i++)
    printf("%d ", i);

A. 0 1 2 3 4
B. 1 2 3 4 5
C. 1 2 3 4
D. 5 4 3 2 1

Question 25

What is the output?

int i = 5;

while (i >= 1)
{
    printf("%d ", i);
    i -= 2;
}

A. 5 4 3 2 1
B. 5 3 1
C. 5 2
D. 1 3 5

Question 26

What is the output?

int i = 10;

do
{
    printf("%d", i);
}
while (i < 5);

A. No output
B. 5
C. 10
D. Infinite loop

Question 27

What is the output?

int i;

for (i = 1; i <= 5; i++)
{
    if (i == 3)
        continue;

    printf("%d ", i);
}

A. 1 2 3 4 5
B. 1 2
C. 1 2 4 5
D. 3 4 5

Question 28

What is the output?

int i;

for (i = 1; i <= 5; i++)
{
    if (i == 3)
        break;

    printf("%d ", i);
}

A. 1 2
B. 1 2 3
C. 1 2 4 5
D. 3 4 5

Question 29

What is the output?

int i;
int sum = 0;

for (i = 1; i <= 4; i++)
    sum += i;

printf("%d", sum);

A. 6
B. 8
C. 10
D. 15

Question 30

What is the output?

int i, j;
int count = 0;

for (i = 1; i <= 3; i++)
{
    for (j = 1; j <= 2; j++)
    {
        count++;
    }
}

printf("%d", count);

A. 3
B. 5
C. 6
D. 9

✅ Answer Key + Direct Solutions

Answer Key

Q.	Answer	Q.	Answer	Q.	Answer
1	B	11	A	21	B
2	C	12	C	22	B
3	C	13	A	23	C
4	C	14	B	24	B
5	B	15	A	25	B
6	C	16	C	26	C
7	C	17	D	27	C
8	C	18	A	28	A
9	B	19	A	29	C
10	C	20	A	30	C

Direct Solutions

1. Answer: B

Dennis Ritchie

2. Answer: C

total_marks

3. Answer: C

sizeof(char) = 1

4. Answer: C

%zu

5. Answer: B

Equality operator = ==

6. Answer: C

Bitwise XOR = ^

7. Answer: C

* before +

8. Answer: C

do-while: minimum one execution

9. Answer: B

break

10. Answer: C

break stops fall-through

11. Answer: A

2 + 3 * 4
= 2 + 12
= 14

12. Answer: C

(2 + 3) * 4
= 5 * 4
= 20

13. Answer: A

7 / 2
= 3

14. Answer: B

7.0 / 2
= 3.5

15. Answer: A

17 % 5
= 2

16. Answer: C

x = 5
y = x++ → y = 5
x = 6

Output: 6 5

17. Answer: D

x = 5
y = ++x
x = 6
y = 6

Output: 6 6

18. Answer: A

5 > 3 = 1
2 < 1 = 0

1 && 0 = 0

19. Answer: A

12 = 1100
10 = 1010

1100 & 1010 = 1000 = 8
1100 | 1010 = 1110 = 14
1100 ^ 1010 = 0110 = 6

Output: 8 14 6

20. Answer: A

0 && ++x

First operand = 0
++x is not executed

x = 0
y = 0

Output: 0 0

21. Answer: B

7 % 2 = 1

Output: Odd

22. Answer: B

80 >= 90 → 0
80 >= 75 → 1

Output: B

23. Answer: C

x = 2
Start at case 2

case 2 → B
No break
case 3 → C
break

Output: BC

24. Answer: B

Iteration	i	Output
1	1	1
2	2	2
3	3	3
4	4	4
5	5	5

Output: 1 2 3 4 5

25. Answer: B

Iteration	i	Output	New i
1	5	5	3
2	3	3	1
3	1	1	−1

Output: 5 3 1

26. Answer: C

Body executes before condition.

Output: 10

27. Answer: C

i	Action
1	Print 1
2	Print 2
3	continue
4	Print 4
5	Print 5

Output: 1 2 4 5

28. Answer: A

i	Action
1	Print 1
2	Print 2
3	break

Output: 1 2

29. Answer: C

i	sum before	sum after
1	0	1
2	1	3
3	3	6
4	6	10

Output: 10

30. Answer: C

Outer iterations = 3
Inner iterations per outer loop = 2

count = 3 × 2
      = 6

🎯 DAY 3 Completion Checklist

Know sizeof() for all data types
Can solve operator precedence problems
Can trace for/while loop outputs
Understand break vs continue with examples

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DAY 3 — C Programming Part 1 — Complete Study Material

Phase 1: Technical Theory | Date: 23 July 2026 | Subject: C Programming Basics | Expected Questions: 6–7

📌 Day Overview

Today you will study:

Basic structure of a C program
Tokens, keywords, identifiers, and comments
Data types: char, int, float, and double
Variables and constants
The sizeof operator
Input and output basics
Arithmetic, relational, logical, bitwise, assignment, increment, decrement, and ternary operators
Operator precedence and associativity
if, if-else, nested if, else-if ladder, and switch
for, while, and do-while loops
break and continue
Output-tracing techniques

Five-Hour Study Plan

Hour	Topic
1	C basics, data types, variables, constants, and sizeof
2	Operators
3	Precedence, associativity, and output tracing
4	Decision statements
5	Loops, break, continue, and output tracing

1. C Basics, Data Types, Variables, Constants, and sizeof

1.1 What Is C?

C is a general-purpose programming language.

It was developed by Dennis Ritchie at Bell Laboratories in the early 1970s.

C is widely used for:

Operating systems
Compilers
Embedded systems
Device drivers
Database software
Networking software
System utilities

Why Is C Important?

C provides:

High-level programming features
Low-level memory access
Fast execution
Portability
A small set of keywords
Structured programming

Middle-Level Language

C is often called a middle-level language because it supports:

High-level features such as functions and loops
Low-level features such as pointers, bitwise operations, and direct memory access

This is a textbook description, not an official language category.

1.2 Compiler and Source Code

A C program is written as source code.

A C compiler translates the source code into a form the computer can execute.

C Source Program
       │
       v
   Preprocessor
       │
       v
    Compiler
       │
       v
    Assembler
       │
       v
   Object Code
       │
       v
     Linker
       │
       v
Executable Program

Source File Extension

A C source file commonly uses the extension:

.c

Example:

program.c

1.3 Basic Structure of a C Program

A simple C program is:

#include <stdio.h>

int main(void)
{
    printf("Hello");
    return 0;
}

Line-by-Line Meaning

Preprocessor Directive

#include <stdio.h>

This includes declarations from the standard input/output header.

stdio means standard input/output.
.h means header file.
printf and scanf are declared in stdio.h.

main Function

int main(void)

Execution of a hosted C program begins with the main function.

int means main returns an integer.
void inside the parentheses means that this form of main accepts no parameters.

Opening and Closing Braces

{
}

Braces create a block of statements.

printf

printf("Hello");

printf displays formatted output.

Semicolon

A semicolon normally ends a C statement.

return

return 0;

Returning 0 from main indicates successful program termination.

1.4 C Is Case-Sensitive

C treats uppercase and lowercase letters as different.

These identifiers are different:

age
Age
AGE

These keywords are not the same:

int
INT

Only lowercase int is a C keyword.

1.5 C Tokens

A token is the smallest meaningful unit of a C program.

Main token categories are:

Keywords
Identifiers
Constants
String literals
Operators
Punctuators

Example

int total = 25;

Tokens are:

int
total
=
25
;

1.6 Keywords

A keyword is a reserved word with a predefined meaning in C.

Examples:

Keyword	Purpose
int	Integer type
char	Character type
float	Floating-point type
double	Higher-precision floating-point type
if	Decision statement
else	Alternative decision
switch	Multi-way selection
case	Case label
for	Loop
while	Loop
do	Loop
break	Terminates loop or switch
continue	Skips to next loop iteration
return	Returns from a function
void	Indicates no value or no parameters in specific contexts
const	Makes an object non-modifiable through that name
sizeof	Gives size in bytes

A keyword cannot normally be used as a variable name.

Invalid:

int for = 10;

1.7 Identifiers

An identifier is a name given to a program element.

Examples:

Variable name
Function name
Array name
Structure name

Valid Identifier Rules

An identifier:

Can contain letters, digits, and underscore.
Must not begin with a digit.
Must not contain spaces.
Must not contain symbols such as @, #, %, or -.
Must not be a C keyword.
Is case-sensitive.

Examples

Identifier	Valid?	Reason
total	Yes	Contains letters
total_marks	Yes	Underscore is allowed
marks2	Yes	Digit is not first
_count	Yes	May begin with underscore, though some underscore names are reserved
2marks	No	Begins with a digit
total marks	No	Contains a space
total-marks	No	Contains a hyphen
float	No	It is a keyword

Good Naming Style

Use meaningful names:

totalMarks
student_count
average

Avoid unclear names:

x1
aaa
qqq

Short names such as i and j are commonly used as loop counters.

1.8 Comments

Comments are notes for programmers. They are ignored during normal program execution.

Single-Line Comment

// This is a single-line comment

Single-line comments are supported in C99 and later.

Multi-Line Comment

/* This is
   a multi-line comment */

Important Point

Traditional C comments cannot be nested safely.

Invalid idea:

/* Outer comment /* Inner comment */ */

1.9 Data Types

A data type tells the compiler:

What kind of value is stored
How the value is interpreted
What operations are allowed
How much memory is required

Main Basic Data Types

Data Type	Main Use	Example
char	Character or small integer	'A'
int	Integer	25
float	Single-precision floating-point value	3.14f
double	Double-precision floating-point value	3.14
void	Absence of a value	Function returning nothing

1.10 char Data Type

The char type stores a character code or a small integer.

Example:

char grade = 'A';

A character constant uses single quotation marks:

'A'
'7'
'@'

char and Integer Codes

Characters are stored internally as numeric codes.

In ASCII:

'A' = 65
'a' = 97
'0' = 48

Example:

char ch = 'A';
printf("%d", ch);

Output on an ASCII-based system:

Guaranteed Size

In C:

sizeof(char) = 1

This is always one C byte.

A C byte contains at least 8 bits. On most modern systems, one byte is 8 bits.

char Variants

char
signed char
unsigned char

A plain char may behave as signed or unsigned depending on the implementation.

1.11 int Data Type

The int type stores whole numbers.

Examples:

int age = 20;
int temperature = -5;
int total = 1000;

It does not store a fractional part.

Integer Type Modifiers

signed
unsigned
short
long
long long

Examples:

short int a;
unsigned int b;
long int c;
long long int d;

These shorter forms are also valid:

short a;
unsigned b;
long c;
long long d;

1.12 Signed and Unsigned Integers

A signed integer can represent:

Negative numbers
Zero
Positive numbers

An unsigned integer represents:

Zero
Positive numbers

For an unsigned n-bit integer:

Range = 0 to 2ⁿ − 1

Example for 8 bits:

0 to 2⁸ − 1
= 0 to 255

For a typical n-bit two’s-complement signed integer:

Range = −2ⁿ⁻¹ to 2ⁿ⁻¹ − 1

Example for 8 bits:

−128 to 127

1.13 float Data Type

The float type stores real numbers with fractional parts.

Example:

float price = 12.5f;

The suffix f makes 12.5f a float constant.

Without f, a decimal floating constant such as 12.5 has type double.

Typical Precision

A float commonly provides about 6–7 significant decimal digits.

Example:

float x = 3.1415926f;

1.14 double Data Type

The double type stores floating-point values with greater precision than float.

Example:

double distance = 12345.6789;

Typical Precision

A double commonly provides about 15–16 significant decimal digits.

long double

long double provides at least as much precision as double.

Example:

long double value = 3.14L;

The suffix L indicates a long double constant.

1.15 void Data Type

void means the absence of a value in specific contexts.

Function Returning No Value

void showMessage(void)
{
    printf("Hello");
}

No Function Parameters

int main(void)

Here, void means the function accepts no parameters.

sizeof(void)

Standard C does not define sizeof(void). Some compilers accept it as an extension, but it should not be used in standard C.

1.16 Sizes of C Data Types

Important Accuracy Rule

The C language does not fix one exact byte size for every data type.

The exact size can depend on:

Compiler
Processor
Operating system
Data model

The only exact basic rule here is:

sizeof(char) = 1

The following relationships are guaranteed:

sizeof(char) ≤ sizeof(short)
sizeof(short) ≤ sizeof(int)
sizeof(int) ≤ sizeof(long)
sizeof(long) ≤ sizeof(long long)

Common Sizes on Modern Systems

Type	Common Size	Typical Purpose
char	1 byte	Character or small integer
short	2 bytes	Small integer
int	4 bytes	General integer
long	4 or 8 bytes	Larger integer
long long	8 bytes	Large integer
float	4 bytes	Single-precision real number
double	8 bytes	Double-precision real number
long double	8, 12, or 16 bytes	Extended precision

Common Competitive-Exam Table

Many basic examinations expect:

Data Type	Commonly Expected Size
char	1 byte
short int	2 bytes
int	4 bytes
long int	4 or 8 bytes
long long int	8 bytes
float	4 bytes
double	8 bytes
long double	Implementation-dependent

If a question names a compiler or architecture, use the sizes for that environment.

1.17 Minimum Ranges Required by C

Type	Minimum Required Range
signed char	−127 to 127
unsigned char	0 to 255
short	−32767 to 32767
unsigned short	0 to 65535
int	At least −32767 to 32767
unsigned int	At least 0 to 65535
long	At least −2147483647 to 2147483647
unsigned long	At least 0 to 4294967295
long long	At least −9223372036854775807 to 9223372036854775807

Modern two’s-complement systems commonly include the additional most-negative value, such as −128 for 8-bit signed char.

1.18 The sizeof Operator

The sizeof operator returns the size of a type or object in bytes.

Syntax

sizeof(type)

or:

sizeof expression

Examples

sizeof(char)
sizeof(int)
sizeof(double)

int x;
sizeof(x)

Example Program

#include <stdio.h>

int main(void)
{
    printf("%zu", sizeof(int));
    return 0;
}

%zu is the correct printf format specifier for the result of sizeof.

Important Rules

sizeof(char) is always 1.
sizeof returns an unsigned integer type called size_t.
Parentheses are required when a type name is used.
Parentheses are usually optional for an ordinary expression.
sizeof does not usually evaluate its operand.

Example:

int x = 5;
printf("%zu %d", sizeof(x++), x);

For an ordinary non-variable-length object, x++ is not executed inside sizeof.

Typical output when int is 4 bytes:

4 5

sizeof an Array

int a[10];

sizeof(a)

If int is 4 bytes:

sizeof(a) = 10 × 4 = 40 bytes

Within the same scope where a is an actual array:

Number of elements = sizeof(a) / sizeof(a[0])

1.19 Variables

A variable is a named memory location whose stored value can change.

Declaration

int age;

This tells the compiler that age is an integer variable.

Initialization

int age = 20;

Initialization gives the variable its first value when it is created.

Assignment

age = 25;

Assignment changes its value.

Multiple Variables

int a, b, c;

Multiple Initializations

int a = 10, b = 20, c = 30;

1.20 Local Variables and Initialization

A local automatic variable that is not initialized has an indeterminate value.

Example:

int main(void)
{
    int x;
    printf("%d", x);
}

This program has undefined behaviour because x is read without initialization.

Always initialize variables before reading them.

Correct:

int x = 0;

1.21 Constants

A constant is a fixed value that does not change during program execution.

Integer Constants

Examples:

10
-25
1000

Integer Bases in C

Form	Example	Meaning
Decimal	25	Decimal 25
Octal	031	Decimal 25
Hexadecimal	0x19	Decimal 25

Important Point

An integer literal beginning with 0 is traditionally interpreted as octal.

010 = decimal 8

019 is invalid as an octal integer because 9 is not an octal digit.

Floating Constants

Examples:

3.14
-0.25
6.02e23
1.5f
2.0L

Scientific notation:

6.02e23 = 6.02 × 10²³

Suffixes:

f or F: float
l or L: long double

Character Constants

A character constant uses single quotes:

'A'
'7'
'\n'

A character constant represents an integer character code.

String Literals

A string literal uses double quotes:

"Hello"
"A"
"123"

Character vs String

Character Constant	String Literal
'A'	"A"
Single quotes	Double quotes
Represents one character code	Represents a sequence ending with a null character

Escape Sequences

An escape sequence represents a special character.

Escape Sequence	Meaning
\n	New line
\t	Horizontal tab
\b	Backspace
\r	Carriage return
\	Backslash
'	Single quotation mark
"	Double quotation mark
\0	Null character

Example:

printf("A\nB");

Output:

A
B

Symbolic Constants with const

const int MAX = 100;

MAX should not later be assigned another value through that name.

Invalid:

MAX = 200;

Symbolic Constants with #define

#define PI 3.14159

The preprocessor replaces PI with 3.14159 before compilation.

const vs #define

const	#define
Declares a typed object	Creates a preprocessor macro
Processed by compiler	Processed before compilation
Obeys scope rules	Macro scope follows preprocessing rules
Has a data type	Simple replacement has no C data type by itself

1.22 Basic Input and Output

printf

printf displays formatted output.

printf("Hello");

Format Specifiers

Data Type	printf Format
int	%d or %i
unsigned int	%u
long int	%ld
long long int	%lld
char	%c
float expression	%f
double	%f
long double	%Lf
String	%s
Hexadecimal integer	%x or %X
Octal integer	%o
sizeof result	%zu

Example

int age = 20;
printf("%d", age);

Output:

scanf

scanf reads formatted input.

int age;
scanf("%d", &age);

The & operator gives the address of age.

Common scanf Formats

Data Type	scanf Format
int	%d
char	%c
float	%f
double	%lf
long double	%Lf

Important:

printf uses %f for a double argument.
scanf uses %f for float and %lf for double.

1.23 Type Conversion

Type conversion changes a value from one data type to another.

Implicit Conversion

The compiler performs it automatically.

int x = 5;
double y = x;

x is converted to double.

Explicit Conversion

The programmer requests conversion using a cast.

double result = (double)5 / 2;

Without the cast:

5 / 2 = 2

With the cast:

(double)5 / 2 = 2.5

Type Cast Syntax

(target_type) expression

Example:

(float)a
(int)x

2. Operators

An operator is a symbol that performs an operation on one or more operands.

Example:

a + b

- is the operator.
a and b are operands.

2.2 Arithmetic Operators

Operator	Operation	Example
+	Addition	a + b
-	Subtraction	a - b
*	Multiplication	a * b
/	Division	a / b
%	Remainder	a % b

Integer Division

When both operands are integers, the result is an integer.

The fractional part is discarded toward zero.

7 / 2 = 3
9 / 4 = 2
-7 / 2 = -3

To get a floating-point result:

7.0 / 2 = 3.5

or:

(double)7 / 2 = 3.5

Remainder Operator

The % operator returns the remainder after integer division.

7 % 2 = 1
10 % 3 = 1
15 % 5 = 0

The operands of % must have integer types.

Invalid:

5.5 % 2.0

Common Use: Even or Odd

if (number % 2 == 0)
    printf("Even");
else
    printf("Odd");

Division by Zero

Division or remainder by integer zero is undefined.

Invalid:

10 / 0
10 % 0

2.3 Unary Plus and Minus

Unary operators work on one operand.

int a = 5;
int b = -a;

Now b is −5.

Examples:

+a
-a

2.4 Relational Operators

Relational operators compare values.

Operator	Meaning
<	Less than
>	Greater than
<=	Less than or equal to
>=	Greater than or equal to
==	Equal to
!=	Not equal to

In C:

True relational result is 1.
False relational result is 0.

Examples:

5 > 3   gives 1
5 < 3   gives 0
5 == 5  gives 1
5 != 5  gives 0

Assignment vs Equality

=   assignment
==  equality comparison

Example:

x = 5;

stores 5 in x.

x == 5

checks whether x equals 5.

2.5 Logical Operators

Logical operators combine or reverse conditions.

Operator	Meaning
&&	Logical AND
\|\|	Logical OR
!	Logical NOT

In C:

Zero is false.
Any non-zero value is true.
Logical results are 0 or 1.

Logical AND

A && B is true only when both operands are true.

A	B	A && B
0	0	0
0	1	0
1	0	0
1	1	1

Example:

(5 > 2) && (8 > 3)
= 1 && 1
= 1

Logical OR

A || B is true when at least one operand is true.

A	B	A \|\| B
0	0	0
0	1	1
1	0	1
1	1	1

Logical NOT

! reverses the logical value.

!0 = 1
!1 = 0
!25 = 0

Short-Circuit Evaluation

Logical AND

For:

A && B

If A is false, B is not evaluated.

Example:

int x = 0;
int y = 0 && ++x;

x remains 0.

Logical OR

For:

A || B

If A is true, B is not evaluated.

Example:

int x = 0;
int y = 1 || ++x;

x remains 0.

2.6 Bitwise Operators

Bitwise operators work on individual bits of integer operands.

Operator	Meaning
&	Bitwise AND
\|	Bitwise OR
^	Bitwise XOR
~	Bitwise complement
<<	Left shift
>>	Right shift

Do not confuse:

Logical	Bitwise
&&	&
\|\|	\|
Works with truth values	Works on individual bits

Bitwise AND

A result bit is 1 only when both input bits are 1.

A	B	A & B
0	0	0
0	1	0
1	0	0
1	1	1

Example:

Therefore:

12 & 10 = 8

Bitwise OR

A result bit is 1 when at least one input bit is 1.

Therefore:

12 | 10 = 14

Bitwise XOR

XOR produces 1 when the bits are different.

A	B	A ^ B
0	0	0
0	1	1
1	0	1
1	1	0

Example:

Therefore:

12 ^ 10 = 6

XOR Properties

x ^ 0 = x
x ^ x = 0

Bitwise Complement

~ changes every bit:

0 becomes 1.
1 becomes 0.

On a common two’s-complement system:

~x = −x − 1

Example:

~5 = −6

The exact visible bit pattern depends on the integer width.

Left Shift

x << n

Shifts bits n positions to the left.

For a non-negative value when the result is representable:

x << n is equivalent to x × 2ⁿ

Example:

Therefore:

5 << 1 = 10

Right Shift

x >> n

Shifts bits n positions to the right.

For non-negative integers:

x >> n is equivalent to integer division by 2ⁿ

Example:

20 >> 2

20 / 4 = 5

Therefore:

20 >> 2 = 5

Avoid relying on right-shift details for negative signed integers in basic output questions because the result is implementation-defined.

2.7 Assignment Operators

Simple Assignment

x = 10;

The right-side value is stored in the left-side object.

Assignment associates from right to left.

a = b = 5;

This works as:

a = (b = 5);

Both a and b become 5.

Compound Assignment

Operator	Meaning
+=	Add and assign
-=	Subtract and assign
*=	Multiply and assign
/=	Divide and assign
%=	Remainder and assign
&=	Bitwise AND and assign
\|=	Bitwise OR and assign
^=	Bitwise XOR and assign
<<=	Left shift and assign
>>=	Right shift and assign

Examples:

x += 3;

means approximately:

x = x + 3;

If x is 5, it becomes 8.

2.8 Increment and Decrement

Increment

The ++ operator increases a variable by 1.

x++;

or:

++x;

Decrement

The -- operator decreases a variable by 1.

x--;

or:

--x;

Prefix Increment

++x

The value is increased before the expression uses it.

Example:

int x = 5;
int y = ++x;

Result:

x = 6
y = 6

Postfix Increment

x++

The old value is used first, and then x is increased.

Example:

int x = 5;
int y = x++;

Result:

y = 5
x = 6

Prefix Decrement

int x = 5;
int y = --x;

Result:

x = 4
y = 4

Postfix Decrement

int x = 5;
int y = x--;

Result:

y = 5
x = 4

Unsafe Increment Expressions

Do not try to predict expressions that modify the same variable multiple times without proper sequencing.

Examples to avoid:

i = i++ + ++i;
printf("%d %d", i++, i);
a[i] = i++;

Such expressions may have undefined behaviour. They do not have one reliable output.

Use separate statements:

int old = i;
i++;
printf("%d %d", old, i);

2.9 Conditional or Ternary Operator

The conditional operator uses three operands.

Syntax

condition ? expression_if_true : expression_if_false

Example

int max = (a > b) ? a : b;

If a is greater than b, max receives a. Otherwise, max receives b.

Example

int x = 10;
printf("%s", (x % 2 == 0) ? "Even" : "Odd");

Output:

Even

It is called the ternary operator because it uses three operands.

2.10 The Comma Operator

The comma operator evaluates expressions from left to right and produces the value of the last expression.

Example:

int x;
x = (2, 4, 6);

x becomes:

Do not confuse the comma operator with commas used to separate function arguments or declarations.

3. Operator Precedence and Associativity

3.1 What Is Precedence?

Precedence decides which operator binds more strongly when an expression contains different operators.

Example:

2 + 3 * 4

Multiplication has higher precedence:

2 + (3 * 4)
= 2 + 12
= 14

Not:

(2 + 3) * 4 = 20

3.2 What Is Associativity?

Associativity decides the grouping direction when operators have the same precedence.

Left-to-Right Example

Multiplication and division have the same precedence and associate left to right:

24 / 6 * 2
= (24 / 6) * 2
= 4 * 2
= 8

Right-to-Left Example

Assignment associates right to left:

a = b = 10

Grouping:

a = (b = 10)

3.3 C Operator Precedence Table

The table goes from highest precedence to lowest.

Level	Operators	Meaning	Associativity
1	() [] . -> postfix ++ postfix --	Postfix operations	Left to right
2	prefix ++ prefix -- + - ! ~ (type) * & sizeof	Unary operations	Right to left
3	* / %	Multiplication, division, remainder	Left to right
4	+ -	Addition, subtraction	Left to right
5	<< >>	Bit shifts	Left to right
6	< <= > >=	Relational	Left to right
7	== !=	Equality	Left to right
8	&	Bitwise AND	Left to right
9	^	Bitwise XOR	Left to right
10	\|	Bitwise OR	Left to right
11	&&	Logical AND	Left to right
12	\|\|	Logical OR	Left to right
13	?:	Conditional	Right to left
14	= += -= *= /= %= &= ^= \|= <<= >>=	Assignment	Right to left
15	,	Comma	Left to right

3.4 Precedence Memory Order

Memorize this practical order:

Parentheses
Postfix increment/decrement
Unary operators
Multiplication, division, remainder
Addition, subtraction
Shifts
Relational
Equality
Bitwise AND
Bitwise XOR
Bitwise OR
Logical AND
Logical OR
Ternary
Assignment
Comma

3.5 Important Expression Examples

Example 1

5 + 2 * 3

= 5 + 6
= 11

Example 2

(5 + 2) * 3

= 7 * 3
= 21

Example 3

20 / 5 * 2

Same precedence, left to right:

= (20 / 5) * 2
= 4 * 2
= 8

Example 4

10 - 4 - 2

Left to right:

= (10 - 4) - 2
= 6 - 2
= 4

Example 5

5 > 3 && 2 < 4

Relational operators are evaluated before logical AND:

= 1 && 1
= 1

Example 6

5 == 5 || 3 > 8

= 1 || 0
= 1

Example 7

4 + 2 << 1

Addition has higher precedence than shift:

= (4 + 2) << 1
= 6 << 1
= 12

Example 8

10 & 6 == 2

Equality has higher precedence than bitwise AND:

= 10 & (6 == 2)
= 10 & 0
= 0

Use parentheses when the intended grouping could be unclear:

(10 & 6) == 2

10 & 6 = 2
2 == 2 = 1

3.6 Best Rule for Real Programs

Do not depend on memory alone for complicated expressions.

Use parentheses:

result = (a + b) * c;

Parentheses improve:

Correctness
Readability
Maintenance
Output tracing

4. Decision and Control Statements

A control statement changes the normal order in which statements execute.

Decision statements include:

if
if-else
nested if
else-if ladder
switch

4.1 Simple if Statement

Syntax

if (condition)
{
    statement;
}

If the condition is non-zero, the block runs.

If the condition is zero, the block is skipped.

Example

int age = 20;

if (age >= 18)
{
    printf("Adult");
}

Output:

Adult

4.2 Truth in C

C treats:

0 as false
Any non-zero value as true

Example:

if (5)
    printf("Yes");

Output:

Yes

Example:

if (0)
    printf("Yes");

No output is produced.

4.3 if-else Statement

Syntax

if (condition)
{
    statements_if_true;
}
else
{
    statements_if_false;
}

Example

int number = 7;

if (number % 2 == 0)
    printf("Even");
else
    printf("Odd");

Output:

Odd

4.4 Braces and Single Statements

If an if or else controls only one statement, braces are optional.

if (x > 0)
    printf("Positive");

For multiple statements, use braces:

if (x > 0)
{
    printf("Positive");
    x++;
}

Recommended practice: use braces even for one statement.

4.5 Common Braces Error

if (x > 0)
    printf("Positive");
    printf("Checked");

Only the first printf belongs to the if statement.

The second printf runs regardless of the condition.

Correct:

if (x > 0)
{
    printf("Positive");
    printf("Checked");
}

4.6 Nested if

A nested if is an if statement inside another if statement.

Example

int x = 15;

if (x > 0)
{
    if (x % 2 == 0)
        printf("Positive even");
    else
        printf("Positive odd");
}
else
{
    printf("Not positive");
}

Output:

Positive odd

4.7 Dangling else Rule

An else is matched with the nearest unmatched if.

Example:

if (a > 0)
    if (b > 0)
        printf("Both positive");
    else
        printf("b is not positive");

The else belongs to:

if (b > 0)

Use braces to make the intended structure clear.

4.8 else-if Ladder

Use an else-if ladder when testing several conditions in order.

Syntax

if (condition1)
{
    statements1;
}
else if (condition2)
{
    statements2;
}
else if (condition3)
{
    statements3;
}
else
{
    default_statements;
}

Example

int marks = 75;

if (marks >= 90)
    printf("A");
else if (marks >= 75)
    printf("B");
else if (marks >= 60)
    printf("C");
else
    printf("D");

Output:

Important Point

Only the first true branch runs.

Order matters.

Incorrect order:

if (marks >= 40)
    printf("Pass");
else if (marks >= 75)
    printf("Distinction");

A mark of 80 satisfies marks >= 40 first, so the second test is never reached.

4.9 switch Statement

A switch selects one path using the value of an integer, character, or enumeration expression.

Syntax

switch (expression)
{
    case constant1:
        statements;
        break;

    case constant2:
        statements;
        break;

    default:
        statements;
}

Example

int day = 2;

switch (day)
{
    case 1:
        printf("Monday");
        break;

    case 2:
        printf("Tuesday");
        break;

    case 3:
        printf("Wednesday");
        break;

    default:
        printf("Invalid");
}

Output:

Tuesday

4.10 switch Rules

The switch expression must have an integer, character, or enumeration type.
case labels must be constant integral expressions.
Duplicate case values are not allowed.
default is optional.
break is optional.
The order of case labels does not determine matching.
Only one default label is allowed in one switch.
Character constants can be used as case values.

Example:

switch (grade)
{
    case 'A':
        printf("Excellent");
        break;

    case 'B':
        printf("Good");
        break;
}

4.11 Fall-Through in switch

Without break, execution continues into later cases.

Example:

int x = 2;

switch (x)
{
    case 1:
        printf("A");

    case 2:
        printf("B");

    case 3:
        printf("C");
        break;

    default:
        printf("D");
}

Output:

BC

Execution begins at case 2 and continues through case 3 until break.

4.12 Grouping Cases

Several cases can share one block.

switch (ch)
{
    case 'a':
    case 'e':
    case 'i':
    case 'o':
    case 'u':
        printf("Vowel");
        break;

    default:
        printf("Not a lowercase vowel");
}

4.13 if-else vs switch

if-else	switch
Supports ranges and complex conditions	Compares one expression with constant case values
Can use relational and logical expressions	Uses equality-like matching
Suitable for few or complex choices	Suitable for many fixed choices
Can test floating-point conditions	switch expression cannot have floating type
No automatic fall-through	Fall-through occurs without break

5. Loops

A loop repeats a block of statements.

C provides:

for loop
while loop
do-while loop

5.1 Loop Components

Most loops contain:

Initialization
Condition
Body
Update

Example:

int i = 1;

while (i <= 5)
{
    printf("%d ", i);
    i++;
}

Initialization: i = 1
Condition: i <= 5
Body: printf
Update: i++

5.2 while Loop

The while loop tests the condition before executing the body.

Syntax

initialization;

while (condition)
{
    statements;
    update;
}

Example

int i = 1;

while (i <= 5)
{
    printf("%d ", i);
    i++;
}

Output:

1 2 3 4 5

Entry-Controlled Loop

while is an entry-controlled loop because it checks the condition before entering the body.

It may execute zero times.

Example:

int i = 10;

while (i < 5)
{
    printf("%d", i);
}

The body does not run.

5.3 do-while Loop

The do-while loop executes the body first and tests the condition afterward.

Syntax

initialization;

do
{
    statements;
    update;
}
while (condition);

Important Point

A semicolon is required after the while condition.

Example

int i = 1;

do
{
    printf("%d ", i);
    i++;
}
while (i <= 5);

Output:

1 2 3 4 5

Exit-Controlled Loop

do-while is an exit-controlled loop.

Its body executes at least once.

Example:

int i = 10;

do
{
    printf("%d", i);
}
while (i < 5);

Output:

5.4 for Loop

A for loop places initialization, condition, and update in one line.

Syntax

for (initialization; condition; update)
{
    statements;
}

Example

int i;

for (i = 1; i <= 5; i++)
{
    printf("%d ", i);
}

Output:

1 2 3 4 5

Execution Order

Initialization
     │
     v
  Condition ─── false ───> Exit
     │
    true
     │
     v
    Body
     │
     v
   Update
     │
     └────────────> Condition

Initialization runs once.

Condition is checked before every iteration.

Update runs after each completed iteration.

5.5 for Loop Variations

Counting Down

for (i = 5; i >= 1; i--)
    printf("%d ", i);

Output:

5 4 3 2 1

Update by Two

for (i = 0; i <= 10; i += 2)
    printf("%d ", i);

Output:

0 2 4 6 8 10

Multiple Expressions

for (i = 0, j = 5; i < j; i++, j--)
{
    printf("%d %d\n", i, j);
}

Missing Sections

Each of the three sections can be omitted.

for (;;)
{
    statements;
}

This creates an infinite loop unless something such as break terminates it.

5.6 while vs do-while vs for

Feature	for	while	do-while
Condition checked	Before body	Before body	After body
Minimum executions	0	0	1
Type	Entry-controlled	Entry-controlled	Exit-controlled
Best use	Known or structured repetition	Condition-based repetition	Body must run at least once
Semicolon after condition	No	No	Yes

5.7 Nested Loops

A loop inside another loop is a nested loop.

Example

int i, j;

for (i = 1; i <= 2; i++)
{
    for (j = 1; j <= 3; j++)
    {
        printf("*");
    }

    printf("\n");
}

Output:

***
***

Iteration Count

If the outer loop runs m times and the inner loop runs n times for each outer iteration:

Total inner executions = m × n

Example:

Outer loop = 3 times
Inner loop = 4 times

Total = 3 × 4 = 12

5.8 Infinite Loops

An infinite loop does not terminate naturally.

Examples:

while (1)
{
}

for (;;)
{
}

Accidental infinite loop:

int i = 1;

while (i <= 5)
{
    printf("%d", i);
}

i never changes, so the condition remains true.

5.9 break Statement

break immediately terminates the nearest enclosing:

for loop
while loop
do-while loop
switch statement

Example

int i;

for (i = 1; i <= 10; i++)
{
    if (i == 5)
        break;

    printf("%d ", i);
}

Output:

1 2 3 4

When i becomes 5, break ends the loop.

Nested Loop Rule

break exits only the nearest enclosing loop.

for (i = 1; i <= 2; i++)
{
    for (j = 1; j <= 5; j++)
    {
        if (j == 3)
            break;

        printf("%d ", j);
    }
}

The outer loop continues.

5.10 continue Statement

continue skips the rest of the current iteration and moves to the next iteration.

for Loop Example

int i;

for (i = 1; i <= 5; i++)
{
    if (i == 3)
        continue;

    printf("%d ", i);
}

Output:

1 2 4 5

while Loop Care

In a while loop, update the loop variable before continue if required.

Correct:

int i = 0;

while (i < 5)
{
    i++;

    if (i == 3)
        continue;

    printf("%d ", i);
}

Output:

1 2 4 5

5.11 break vs continue

break	continue
Terminates the loop completely	Skips only the current iteration
Control moves after the loop	Control moves to the next iteration
Also used in switch	Not used to exit switch
Nearest enclosing loop or switch	Nearest enclosing loop

Mnemonic:

break = break out
continue = continue with next iteration

5.12 Common Loop Patterns

Sum of 1 to n

int i;
int sum = 0;

for (i = 1; i <= n; i++)
{
    sum += i;
}

For n = 5:

sum = 1 + 2 + 3 + 4 + 5 = 15

Factorial

The factorial of n is:

n! = n × (n − 1) × ... × 2 × 1

Example:

5! = 5 × 4 × 3 × 2 × 1 = 120

Program pattern:

int i;
int fact = 1;

for (i = 1; i <= n; i++)
{
    fact *= i;
}

Count Digits

int count = 0;

while (n != 0)
{
    n /= 10;
    count++;
}

For n = 538:

538 → 53 → 5 → 0

Count:

Reverse Digits

int reverse = 0;

while (n != 0)
{
    int digit = n % 10;
    reverse = reverse * 10 + digit;
    n /= 10;
}

For n = 123:

reverse = 321

5.13 Output-Tracing Method

Use this process for every output question:

Write the initial value of each variable.
Add parentheses according to precedence.
Follow prefix and postfix rules.
Check integer division.
Check whether a condition is 0 or non-zero.
For loops, create an iteration table.
Track break and continue.
Check switch fall-through.
Reject undefined-behaviour questions instead of inventing an output.

Loop Trace Table Example

For:

int i;
int sum = 0;

for (i = 1; i <= 3; i++)
    sum += i;

Iteration	i	sum before	sum after
1	1	0	1
2	2	1	3
3	3	3	6

Final sum:

🔑 Quick Revision Sheet

Basic C Structure

#include <stdio.h>

int main(void)
{
    statements;
    return 0;
}

Common Data Types

Type	Common Size	Use
char	1 byte	Character/small integer
short	2 bytes	Small integer
int	4 bytes	Integer
long	4 or 8 bytes	Larger integer
long long	8 bytes	Large integer
float	4 bytes	Single-precision real
double	8 bytes	Double-precision real

Only this is universally exact:

sizeof(char) = 1

Other exact sizes depend on the implementation.

Format Specifiers

Type	printf	scanf
int	%d	%d
unsigned int	%u	%u
char	%c	%c
float	%f	%f
double	%f	%lf
long int	%ld	%ld
long long int	%lld	%lld
long double	%Lf	%Lf
sizeof result	%zu	—

Operator Rules

Arithmetic

+  -  *  /  %

Relational

<  <=  >  >=  ==  !=

Logical

&&  ||  !

Bitwise

&  |  ^  ~  <<  >>

Assignment

=  +=  -=  *=  /=  %=

Increment and Decrement

++x  x++  --x  x--

Ternary

condition ? true_value : false_value

Practical Precedence Order

Parentheses and postfix
Unary
Multiplication, division, remainder
Addition and subtraction
Shifts
Relational
Equality
Bitwise AND
Bitwise XOR
Bitwise OR
Logical AND
Logical OR
Ternary
Assignment
Comma

Control Statements

Statement	Use
if	One conditional path
if-else	Two paths
else-if ladder	Multiple conditions
nested if	Decision inside a decision
switch	Fixed constant choices

Loop Comparison

Loop	Condition	Minimum Execution
for	Before body	0
while	Before body	0
do-while	After body	1

break and continue

break terminates the loop or switch.
continue skips the remaining statements in the current loop iteration.
break in a nested loop exits only the nearest loop.
continue does not terminate the complete loop.

📝 Practice Questions

Theory Questions: 1–10

Question 1

Who developed the C programming language?

A. James Gosling
B. Dennis Ritchie
C. Bjarne Stroustrup
D. Guido van Rossum

Question 2

Which is a valid C identifier?

A. 2marks
B. total-marks
C. total_marks
D. float

Question 3

Which statement is guaranteed by standard C?

A. sizeof(int) is always 2
B. sizeof(int) is always 4
C. sizeof(char) is always 1
D. sizeof(double) is always 8

Question 4

Which format specifier is used with printf for a value returned by sizeof?

A. %d
B. %f
C. %zu
D. %c

Question 5

Which operator tests equality?

A. =
B. ==
C. !=
D. <=

Question 6

Which operator performs bitwise XOR?

A. &&
B. ||
C. ^
D. ~

Question 7

Which operator has higher precedence?

A. Addition over multiplication
B. Logical OR over logical AND
C. Multiplication over addition
D. Assignment over equality

Question 8

Which loop always executes its body at least once?

A. for
B. while
C. do-while
D. None of these

Question 9

Which statement immediately terminates the nearest enclosing loop?

A. continue
B. break
C. case
D. sizeof

Question 10

Which statement about switch is correct?

A. Its expression must always be a float.
B. Duplicate case values are permitted.
C. break prevents fall-through to later cases.
D. default is compulsory.

Operator and Expression Output Questions: 11–20

Assume stdio.h is included and each fragment is placed correctly inside main.

Question 11

What is the output?

printf("%d", 2 + 3 * 4);

A. 14
B. 20
C. 24
D. 11

Question 12

What is the output?

printf("%d", (2 + 3) * 4);

A. 14
B. 18
C. 20
D. 24

Question 13

What is the output?

int x = 7 / 2;
printf("%d", x);

A. 3
B. 3.5
C. 4
D. 2

Question 14

What is the output?

printf("%.1f", 7.0 / 2);

A. 3.0
B. 3.5
C. 4.0
D. 7.0

Question 15

What is the output?

printf("%d", 17 % 5);

A. 2
B. 3
C. 4
D. 5

Question 16

What is the output?

int x = 5;
int y = x++;
printf("%d %d", x, y);

A. 5 5
B. 5 6
C. 6 5
D. 6 6

Question 17

What is the output?

int x = 5;
int y = ++x;
printf("%d %d", x, y);

A. 5 5
B. 5 6
C. 6 5
D. 6 6

Question 18

What is the output?

printf("%d", (5 > 3) && (2 < 1));

A. 0
B. 1
C. 2
D. 5

Question 19

What is the output?

printf("%d %d %d", 12 & 10, 12 | 10, 12 ^ 10);

A. 8 14 6
B. 14 8 6
C. 8 6 14
D. 6 14 8

Question 20

What is the output?

int x = 0;
int y = 0 && ++x;
printf("%d %d", x, y);

A. 0 0
B. 1 0
C. 1 1
D. 0 1

Control Statements and Loop Output Questions: 21–30

Question 21

What is the output?

int x = 7;

if (x % 2 == 0)
    printf("Even");
else
    printf("Odd");

A. Even
B. Odd
C. 7
D. No output

Question 22

What is the output?

int marks = 80;

if (marks >= 90)
    printf("A");
else if (marks >= 75)
    printf("B");
else if (marks >= 60)
    printf("C");
else
    printf("D");

A. A
B. B
C. C
D. D

Question 23

What is the output?

int x = 2;

switch (x)
{
    case 1:
        printf("A");

    case 2:
        printf("B");

    case 3:
        printf("C");
        break;

    default:
        printf("D");
}

A. A
B. B
C. BC
D. BCD

Question 24

What is the output?

int i;

for (i = 1; i <= 5; i++)
    printf("%d ", i);

A. 0 1 2 3 4
B. 1 2 3 4 5
C. 1 2 3 4
D. 5 4 3 2 1

Question 25

What is the output?

int i = 5;

while (i >= 1)
{
    printf("%d ", i);
    i -= 2;
}

A. 5 4 3 2 1
B. 5 3 1
C. 5 2
D. 1 3 5

Question 26

What is the output?

int i = 10;

do
{
    printf("%d", i);
}
while (i < 5);

A. No output
B. 5
C. 10
D. Infinite loop

Question 27

What is the output?

int i;

for (i = 1; i <= 5; i++)
{
    if (i == 3)
        continue;

    printf("%d ", i);
}

A. 1 2 3 4 5
B. 1 2
C. 1 2 4 5
D. 3 4 5

Question 28

What is the output?

int i;

for (i = 1; i <= 5; i++)
{
    if (i == 3)
        break;

    printf("%d ", i);
}

A. 1 2
B. 1 2 3
C. 1 2 4 5
D. 3 4 5

Question 29

What is the output?

int i;
int sum = 0;

for (i = 1; i <= 4; i++)
    sum += i;

printf("%d", sum);

A. 6
B. 8
C. 10
D. 15

Question 30

What is the output?

int i, j;
int count = 0;

for (i = 1; i <= 3; i++)
{
    for (j = 1; j <= 2; j++)
    {
        count++;
    }
}

printf("%d", count);

A. 3
B. 5
C. 6
D. 9

✅ Answer Key + Direct Solutions

Answer Key

Q.	Answer	Q.	Answer	Q.	Answer
1	B	11	A	21	B
2	C	12	C	22	B
3	C	13	A	23	C
4	C	14	B	24	B
5	B	15	A	25	B
6	C	16	C	26	C
7	C	17	D	27	C
8	C	18	A	28	A
9	B	19	A	29	C
10	C	20	A	30	C

Direct Solutions

1. Answer: B

Dennis Ritchie

2. Answer: C

total_marks

3. Answer: C

sizeof(char) = 1

4. Answer: C

%zu

5. Answer: B

Equality operator = ==

6. Answer: C

Bitwise XOR = ^

7. Answer: C

* before +

8. Answer: C

do-while: minimum one execution

9. Answer: B

break

10. Answer: C

break stops fall-through

11. Answer: A

2 + 3 * 4
= 2 + 12
= 14

12. Answer: C

(2 + 3) * 4
= 5 * 4
= 20

13. Answer: A

7 / 2
= 3

14. Answer: B

7.0 / 2
= 3.5

15. Answer: A

17 % 5
= 2

16. Answer: C

x = 5
y = x++ → y = 5
x = 6

Output: 6 5

17. Answer: D

x = 5
y = ++x
x = 6
y = 6

Output: 6 6

18. Answer: A

5 > 3 = 1
2 < 1 = 0

1 && 0 = 0

19. Answer: A

12 = 1100
10 = 1010

1100 & 1010 = 1000 = 8
1100 | 1010 = 1110 = 14
1100 ^ 1010 = 0110 = 6

Output: 8 14 6

20. Answer: A

0 && ++x

First operand = 0
++x is not executed

x = 0
y = 0

Output: 0 0

21. Answer: B

7 % 2 = 1

Output: Odd

22. Answer: B

80 >= 90 → 0
80 >= 75 → 1

Output: B

23. Answer: C

x = 2
Start at case 2

case 2 → B
No break
case 3 → C
break

Output: BC

24. Answer: B

Iteration	i	Output
1	1	1
2	2	2
3	3	3
4	4	4
5	5	5

Output: 1 2 3 4 5

25. Answer: B

Iteration	i	Output	New i
1	5	5	3
2	3	3	1
3	1	1	−1

Output: 5 3 1

26. Answer: C

Body executes before condition.

Output: 10

27. Answer: C

i	Action
1	Print 1
2	Print 2
3	continue
4	Print 4
5	Print 5

Output: 1 2 4 5

28. Answer: A

i	Action
1	Print 1
2	Print 2
3	break

Output: 1 2

29. Answer: C

i	sum before	sum after
1	0	1
2	1	3
3	3	6
4	6	10

Output: 10

30. Answer: C

Outer iterations = 3
Inner iterations per outer loop = 2

count = 3 × 2
      = 6

🎯 DAY 3 Completion Checklist

Know sizeof() for all data types
Can solve operator precedence problems
Can trace for/while loop outputs
Understand break vs continue with examples

Q.	Answer	Q.	Answer	Q.	Answer
1	B	11	A	21	B
2	C	12	C	22	B
3	C	13	A	23	C
4	C	14	B	24	B
5	B	15	A	25	B
6	C	16	C	26	C
7	C	17	D	27	C
8	C	18	A	28	A
9	B	19	A	29	C
10	C	20	A	30	C

Q.	Answer	Q.	Answer	Q.	Answer
1	B	11	A	21	B
2	C	12	C	22	B
3	C	13	A	23	C
4	C	14	B	24	B
5	B	15	A	25	B
6	C	16	C	26	C
7	C	17	D	27	C
8	C	18	A	28	A
9	B	19	A	29	C
10	C	20	A	30	C

Q.	Answer	Q.	Answer	Q.	Answer
1	B	11	A	21	B
2	C	12	C	22	B
3	C	13	A	23	C
4	C	14	B	24	B
5	B	15	A	25	B
6	C	16	C	26	C
7	C	17	D	27	C
8	C	18	A	28	A
9	B	19	A	29	C
10	C	20	A	30	C

Q.	Answer	Q.	Answer	Q.	Answer
1	B	11	A	21	B
2	C	12	C	22	B
3	C	13	A	23	C
4	C	14	B	24	B
5	B	15	A	25	B
6	C	16	C	26	C
7	C	17	D	27	C
8	C	18	A	28	A
9	B	19	A	29	C
10	C	20	A	30	C

Q.	Answer	Q.	Answer	Q.	Answer
1	B	11	A	21	B
2	C	12	C	22	B
3	C	13	A	23	C
4	C	14	B	24	B
5	B	15	A	25	B
6	C	16	C	26	C
7	C	17	D	27	C
8	C	18	A	28	A
9	B	19	A	29	C
10	C	20	A	30	C

Q.	Answer	Q.	Answer	Q.	Answer
1	B	11	A	21	B
2	C	12	C	22	B
3	C	13	A	23	C
4	C	14	B	24	B
5	B	15	A	25	B
6	C	16	C	26	C
7	C	17	D	27	C
8	C	18	A	28	A
9	B	19	A	29	C
10	C	20	A	30	C