do-while Loop in C

Introduction

do-while Loop in C is a looping statement used to execute a block of code repeatedly while a condition remains true. Unlike the while loop, the do-while loop executes the loop body at least once before checking the condition.

In this C Programming Course in Jaipur, students learn the syntax, flow, working, and applications of the do-while loop in C programming.

What is do-while Loop in C?

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

Syntax:

do {
    // code
} while(condition);

The loop body always executes at least one time.

Flow of do-while Loop

Execute Loop Body → Check Condition → True → Repeat
Execute Loop Body → Check Condition → False → Exit Loop

The do-while loop is also called:

Exit Controlled Loop

because the condition is checked after execution.

Example of do-while Loop

#include<stdio.h>

int main() {

    int i = 1;

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

    return 0;
}

Output:

1
2
3
4
5

Understanding the Example

Initialization

int i = 1;

The loop starts from 1.

Loop Body

printf("%d\n", i);
i++;

The value is printed and incremented.

Condition

i <= 5

The loop repeats while the condition is true.

Difference Between while Loop and do-while Loop

Example Showing Difference

while Loop Example

int i = 10;

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

Output:

No Output

do-while Loop Example

int i = 10;

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

Output:

10

The do-while loop executes once even when the condition is false.

Example Using User Input

#include<stdio.h>

int main() {

    int number, sum = 0;

    do {

        printf("Enter a number: ");
        scanf("%d", &number);

        sum += number;

    } while(number != 0);

    printf("Sum = %d", sum);

    return 0;
}

The loop continues until the user enters 0.

Nested do-while Loop

A do-while loop inside another do-while loop is called nested do-while loop.

Example:

#include<stdio.h>

int main() {

    int i = 1;

    do {

        int j = 1;

        do {
            printf("%d %d\n", i, j);
            j++;
        } while(j <= 2);

        i++;

    } while(i <= 3);

    return 0;
}

Output:

1 1
1 2
2 1
2 2
3 1
3 2

Applications of do-while Loop

The do-while loop is commonly used in:

• Menu-driven programs
• ATM systems
• Game menus
• Input validation systems
• Login systems

Students learning C Programming Course in Jaipur use do-while loops in many interactive applications.

Infinite do-while Loop

Example:

do {
    printf("Infinite Loop");
} while(1);

This creates an infinite loop because the condition always remains true.

Common Errors in do-while Loop

Missing Semicolon

Incorrect:

} while(i <= 5)

Correct:

} while(i <= 5);

The semicolon after while(condition) is mandatory.

Missing Increment

Incorrect:

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

This creates an infinite loop.

Correct:

i++;

Best Practices

• Initialize loop variables properly
• Update loop counters correctly
• Avoid unnecessary infinite loops
• Use meaningful conditions
• Keep loops readable and simple

Good loop structure improves program maintainability.

Importance of do-while Loop in C

The do-while loop helps:

• Execute code at least once
• Handle user-driven applications
• Build menu-based systems
• Automate repeated tasks

Understanding do-while loops is essential for practical programming.

Real-World Example

ATM Menu:

do {
    printf("1. Deposit\n");
    printf("2. Withdraw\n");
    printf("3. Exit\n");

    scanf("%d", &choice);

} while(choice != 3);

The menu continues until the user selects Exit.

Summary

do-while Loop in C is an exit-controlled loop that executes code first and checks the condition afterward. It guarantees at least one execution of the loop body.

This lesson explained syntax, flow of execution, examples, nested loops, applications, infinite loops, and best practices for do-while loops in C programming.

FAQs

What is do-while Loop in C?

The do-while loop executes code repeatedly while a condition remains true.

Why is do-while called exit controlled loop?

Because the condition is checked after loop execution.

What is the main difference between while and do-while?

The do-while loop executes at least once even if the condition is false.

Is semicolon mandatory in do-while loop?

Yes, semicolon after while(condition) is mandatory.

Where is do-while loop commonly used?

It is commonly used in menu-driven and interactive applications.

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