1.4 Control Statements in C

Module 1.4 • Execution Mappings, Branching & Loop Structures

1.4.1 Introduction

By default, a C program executes statements one after another from top to bottom. However, many real-world problems require decisions, repetition, or skipping certain instructions.

Control statements allow us to change the normal flow of execution according to program requirements.

Using control statements, we can:

Execute code only when a condition is true.
Repeat a set of statements multiple times.
Skip certain instructions.
Exit from loops when needed.
Transfer control to another part of the program.

Control statements are mainly divided into three categories:

Decision Making Statements
Looping Statements
Jump Statements

1.4.2 Decision Making Statements

Decision-making statements allow a program to choose different actions based on conditions.

A. if Statement

The if statement executes a block of code only when the specified condition is true.

Syntax

if(condition)
{
    statements;
}

Example

#include <stdio.h>
 
int main()
{
    int marks = 78;
 
    if(marks >= 50)
    {
        printf("Pass");
    }
 
    return 0;
}

Output

Pass

B. if...else Statement

The if...else statement provides two possible paths.

Syntax

if(condition)
{
    statements;
}
else
{
    statements;
}

Example

#include <stdio.h>
 
int main()
{
    int age = 16;
 
    if(age >= 18)
    {
        printf("Eligible to Vote");
    }
    else
    {
        printf("Not Eligible to Vote");
    }
 
    return 0;
}

Output

Not Eligible to Vote

C. else-if Ladder

Used when multiple conditions need to be checked.

Example

#include <stdio.h>
 
int main()
{
    int score = 82;
 
    if(score >= 90)
        printf("Grade A");
    else if(score >= 75)
        printf("Grade B");
    else if(score >= 60)
        printf("Grade C");
    else
        printf("Grade D");
 
    return 0;
}

Output

Grade B

Important Note

The moment one condition becomes true, the remaining conditions are skipped.

D. Nested if Statement

An if statement can be placed inside another if statement.

Example

#include <stdio.h>
 
int main()
{
    int age = 24;
    int salary = 35000;
 
    if(age >= 18)
    {
        if(salary >= 30000)
            printf("Loan Approved");
    }
 
    return 0;
}

Output

Loan Approved

E. switch Statement

The switch statement is useful when a variable can have many possible values.

Syntax

switch(expression)
{
    case value1:
        statements;
        break;
 
    case value2:
        statements;
        break;
 
    default:
        statements;
}

Example

#include <stdio.h>
 
int main()
{
    int day = 4;
 
    switch(day)
    {
        case 1:
            printf("Monday");
            break;
 
        case 2:
            printf("Tuesday");
            break;
 
        case 3:
            printf("Wednesday");
            break;
 
        case 4:
            printf("Thursday");
            break;
 
        default:
            printf("Invalid Day");
    }
 
    return 0;
}

Output

Thursday

1.4.3 Looping Statements

Loops are used when a set of statements must be executed repeatedly. C provides three loops:

while
do...while
for

A. while Loop

The condition is checked before executing the loop body.

Syntax

while(condition)
{
    statements;
}

Example

#include <stdio.h>
 
int main()
{
    int n = 1;
 
    while(n <= 5)
    {
        printf("%d ", n);
        n++;
    }
 
    return 0;
}

Output

1 2 3 4 5

B. do...while Loop

The loop body executes first and the condition is checked afterward.

Syntax

do
{
    statements;
}
while(condition);

Example

#include <stdio.h>
 
int main()
{
    int n = 1;
 
    do
    {
        printf("%d ", n);
        n++;
    }
    while(n <= 5);
 
    return 0;
}

Output

1 2 3 4 5

Important Feature

A do...while loop always executes at least one time.

C. for Loop

Used when the number of repetitions is known.

Syntax

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

Example

#include <stdio.h>
 
int main()
{
    int i;
 
    for(i = 1; i <= 5; i++)
    {
        printf("%d ", i);
    }
 
    return 0;
}

Output

1 2 3 4 5

1.4.4 Nested Loops

A loop inside another loop is called a nested loop.

Example

#include <stdio.h>
 
int main()
{
    int i, j;
 
    for(i = 1; i <= 3; i++)
    {
        for(j = 1; j <= 4; j++)
        {
            printf("* ");
        }
 
        printf("\n");
    }
 
    return 0;
}

Output

* * * * * * * * * * * *

1.4.5 Infinite Loops

A loop that never stops executing is called an infinite loop.

Example

while(1)
{
    printf("Running...");
}

Since the condition is always true, the loop continues forever.

Common Causes

Forgetting to update loop variables.
Wrong loop condition.
Using assignment operator (=) instead of equality operator (==).

Example:

while(value = 1)
{
}

This becomes an infinite loop because value = 1 always produces a true value.

1.4.6 break Statement

The break statement immediately terminates a loop or switch block.

Example

#include <stdio.h>
 
int main()
{
    int i;
 
    for(i = 1; i <= 10; i++)
    {
        if(i == 6)
            break;
 
        printf("%d ", i);
    }
 
    return 0;
}

Output

1 2 3 4 5

1.4.7 continue Statement

The continue statement skips the remaining statements of the current iteration and moves to the next iteration.

Example

#include <stdio.h>
 
int main()
{
    int i;
 
    for(i = 1; i <= 5; i++)
    {
        if(i == 3)
            continue;
 
        printf("%d ", i);
    }
 
    return 0;
}

Output

1 2 4 5

1.4.8 goto Statement

The goto statement transfers program control to a labeled statement.

Syntax

goto label;
 
label:
statement;

Example

#include <stdio.h>
 
int main()
{
    int n = 1;
 
start:
 
    printf("%d ", n);
    n++;
 
    if(n <= 4)
        goto start;
 
    return 0;
}

Output

1 2 3 4

Note

Although valid, excessive use of goto can make programs difficult to understand and maintain.

1.4.9 Compound Statement (Block)

A group of statements enclosed within curly braces { } is called a block or compound statement.

Example

{
    int length = 10;
    int width = 5;
 
    printf("%d", length * width);
}

All statements inside the braces are treated as a single unit.

1.4.10 Comparison of Loops

Feature	while	do...while	for
Condition Checked	Before Loop	After Loop	Before Loop
Executes At Least Once	No	Yes	No
Best Used When	Iterations Unknown	Must Run Once	Iterations Known

1.4.11 Real-Life Uses of Control Statements

Decision Making

ATM menu selection
Exam result processing
Login verification

Loops

Printing reports
Processing records
Generating tables

Jump Statements

Exiting menus
Skipping invalid data
Terminating loops early

Summary

Control statements manage the flow of execution in a C program.
Decision statements include if, if...else, else-if, and switch.
Loop statements include while, do...while, and for.
break exits a loop immediately.
continue skips the current iteration.
goto transfers control to a labeled statement.
Nested loops and nested if statements allow complex program logic.
Proper use of control statements makes programs efficient and easy to understand.

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