while and do-while Loops in C Practice Questions with Solutions

Introduction

The while and do-while loops are used when a C program needs to repeat a block of code based on a condition. A while loop checks the condition before executing the loop body, while a do-while loop executes the body at least once before checking the condition. In this chapter, you will practice both loops with 10 easy-to-understand examples covering counting, sums, digits, menus, validation, and practical number problems. while and do-while Loops in C practice questions with solutions to help you understand the concepts.

Q1. Print Numbers from 1 to 10 Using `while`

Problem Statement

Write a C program to print numbers from 1 to 10 using a while loop.

C Program

#include <stdio.h>

int main()
{
    int i = 1;

    while (i <= 10)
    {
        printf("%d\n", i);
        i++;
    }

    return 0;
}

Sample Output

Explanation

The variable starts with:

i = 1;

The while loop checks:

i <= 10

If the condition is true, the loop body executes.

After printing the number, i++ increases its value by 1.

The loop stops when i becomes 11.

Concepts Covered

while loop
Initialization
Condition
Increment
Counter variable

Q2. Print Numbers from 10 to 1

Problem Statement

Write a C program to print numbers from 10 down to 1 using a while loop.

C Program

#include <stdio.h>

int main()
{
    int i = 10;

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

    return 0;
}

Sample Output

Explanation

This time, the counter starts at 10.

After every iteration:

i--;

decreases the value by 1.

The loop continues while:

i >= 1

Concepts Covered

while
Decrement operator
Reverse counting
Loop condition

Q3. Find the Sum of Numbers from 1 to N

Problem Statement

Write a C program that accepts a number N and calculates the sum of numbers from 1 to N using a while loop.

For example:

N = 5

1 + 2 + 3 + 4 + 5 = 15

C Program

#include <stdio.h>

int main()
{
    int n;
    int i = 1;
    int sum = 0;

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

    while (i <= n)
    {
        sum = sum + i;
        i++;
    }

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

    return 0;
}

Sample Output

Enter a number: 5
Sum = 15

Explanation

Initially:

sum = 0;

The loop adds each number to sum:

sum = 0 + 1
sum = 1 + 2
sum = 3 + 3
sum = 6 + 4
sum = 10 + 5

The final result is 15.

Concepts Covered

while loop
Accumulator
Addition
User input

Q4. Count the Digits of a Number

Problem Statement

Write a C program to count how many digits are present in an integer using a while loop.

C Program

#include <stdio.h>

int main()
{
    int number;
    int count = 0;

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

    if (number == 0)
    {
        count = 1;
    }
    else
    {
        if (number < 0)
        {
            number = -number;
        }

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

    printf("Number of digits = %d", count);

    return 0;
}

Sample Output

Enter a number: 5832
Number of digits = 4

Explanation

Every time we divide an integer by 10, its last digit is removed.

For example:

5832 / 10 = 583
583 / 10  = 58
58 / 10   = 5
5 / 10    = 0

The loop runs four times, so the number has four digits.

Concepts Covered

while
Integer division
Digit counting
Negative numbers
if-else

Q5. Find the Sum of Digits

Problem Statement

Write a C program to find the sum of all digits of a number.

For example:

5832

5 + 8 + 3 + 2 = 18

C Program

#include <stdio.h>

int main()
{
    int number;
    int digit;
    int sum = 0;

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

    if (number < 0)
    {
        number = -number;
    }

    while (number != 0)
    {
        digit = number % 10;
        sum = sum + digit;
        number = number / 10;
    }

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

    return 0;
}

Sample Output

Enter a number: 5832
Sum of digits = 18

Explanation

The % operator extracts the last digit:

digit = number % 10;

For 5832:

5832 % 10 = 2
583  % 10 = 3
58   % 10 = 8
5    % 10 = 5

The digits are then added together.

Concepts Covered

while
Modulus operator
Integer division
Digit extraction
Accumulator

Q6. Reverse a Number

Problem Statement

Write a C program to reverse a number using a while loop.

For example:

12345 → 54321

C Program

#include <stdio.h>

int main()
{
    int number;
    int digit;
    int reverse = 0;

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

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

    printf("Reversed number = %d", reverse);

    return 0;
}

Sample Output

Enter a number: 12345
Reversed number = 54321

Explanation

For 12345:

Last digit = 5
reverse = 0 × 10 + 5 = 5

Last digit = 4
reverse = 5 × 10 + 4 = 54

Last digit = 3
reverse = 54 × 10 + 3 = 543

The same process continues until the original number becomes 0.

Concepts Covered

while
% operator
/ operator
Number reversal
Digit extraction

Q7. Check Whether a Number Is Palindrome

Problem Statement

Write a C program to check whether a number is a palindrome.

A palindrome reads the same forward and backward.

Examples:

121 → Palindrome
1331 → Palindrome
123 → Not Palindrome

C Program

#include <stdio.h>

int main()
{
    int number;
    int original;
    int digit;
    int reverse = 0;

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

    original = number;

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

    if (original == reverse)
    {
        printf("The number is a palindrome.");
    }
    else
    {
        printf("The number is not a palindrome.");
    }

    return 0;
}

Sample Output

Enter a number: 1221
The number is a palindrome.

Explanation

First, the original number is saved:

original = number;

Then the number is reversed using the while loop.

Finally:

if (original == reverse)

checks whether the original and reversed numbers are equal.

Concepts Covered

while
Number reversal
if-else
Palindrome logic

Q8. Print Multiplication Table Using `while`

Problem Statement

Write a C program that accepts a number and prints its multiplication table from 1 to 10 using a while loop.

C Program

#include <stdio.h>

int main()
{
    int number;
    int i = 1;

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

    while (i <= 10)
    {
        printf("%d x %d = %d\n", number, i, number * i);
        i++;
    }

    return 0;
}

Sample Output

Enter a number: 8
8 x 1 = 8
8 x 2 = 16
8 x 3 = 24
8 x 4 = 32
8 x 5 = 40
8 x 6 = 48
8 x 7 = 56
8 x 8 = 64
8 x 9 = 72
8 x 10 = 80

Explanation

The counter starts at 1 and continues until 10.

The multiplication is performed using:

number * i

After every iteration:

i++;

moves the counter to the next value.

Concepts Covered

while
Counter
Multiplication
User input

Q9. Create a Simple Menu Using `do-while`

Problem Statement

Create a simple menu using a do-while loop.

The menu should repeatedly display:

1. Say Hello
2. Say Welcome
3. Exit

The program should continue until the user selects 3.

C Program

#include <stdio.h>

int main()
{
    int choice;

    do
    {
        printf("\n===== MENU =====\n");
        printf("1. Say Hello\n");
        printf("2. Say Welcome\n");
        printf("3. Exit\n");

        printf("Enter your choice: ");
        scanf("%d", &choice);

        switch (choice)
        {
            case 1:
                printf("Hello!");
                break;

            case 2:
                printf("Welcome!");
                break;

            case 3:
                printf("Program ended.");
                break;

            default:
                printf("Invalid choice.");
        }

    } while (choice != 3);

    return 0;
}

Sample Output

===== MENU =====
1. Say Hello
2. Say Welcome
3. Exit
Enter your choice: 1
Hello!

===== MENU =====
1. Say Hello
2. Say Welcome
3. Exit
Enter your choice: 2
Welcome!

===== MENU =====
1. Say Hello
2. Say Welcome
3. Exit
Enter your choice: 3
Program ended.

Explanation

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

Here:

do
{
    // menu
}
while (choice != 3);

The menu appears at least once.

The loop continues while the user does not select 3.

Concepts Covered

do-while
switch
Menu-driven program
break
Loop condition

Q10. Keep Asking for a Positive Number Using `do-while`

Problem Statement

Write a C program that repeatedly asks the user to enter a positive number. The program should stop only when the user enters a positive value.

C Program

#include <stdio.h>

int main()
{
    int number;

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

        if (number <= 0)
        {
            printf("Invalid input. Try again.\n");
        }

    } while (number <= 0);

    printf("You entered: %d", number);

    return 0;
}

Sample Output

Enter a positive number: -5
Invalid input. Try again.

Enter a positive number: 0
Invalid input. Try again.

Enter a positive number: 25
You entered: 25

Explanation

The do-while loop is useful here because the program needs to ask for input at least once.

The condition:

number <= 0

means the loop continues when the input is invalid.

When the user enters 25:

25 <= 0 → False

so the loop stops.

Concepts Covered

do-while
Input validation
if
Repeated input
Loop condition

Key Takeaways

while is an entry-controlled loop because it checks the condition before execution.
do-while is an exit-controlled loop because it checks the condition after execution.
A while loop may execute zero times.
A do-while loop executes at least once.
Always make sure the loop variable or condition changes when necessary.
while loops are useful for counting, digit processing, searching, and condition-based repetition.
do-while loops are particularly useful for menus and input validation.
The do-while statement ends with a semicolon after while (condition);.
% 10 can be used to extract the last digit of an integer.
Integer division by 10 can remove the last digit.
while and do-while loops can be combined with if, switch, and other C concepts.
Nested loops can also be created using while or do-while.

FAQs

1. What is a `while` loop in C?

A while loop repeatedly executes a block of code as long as its condition remains true.

while (condition)
{
    // code
}

2. What is a `do-while` loop in C?

A do-while loop executes its body first and then checks the condition.

do
{
    // code
}
while (condition);

3. What is the main difference between `while` and `do-while`?

The main difference is when the condition is checked.

while → condition is checked first.
do-while → condition is checked after the body executes.

Therefore, a do-while loop always executes its body at least once.

4. Can a `while` loop execute zero times?

Yes.

If its condition is false before the first iteration, the loop body will not execute.

int i = 10;

while (i < 5)
{
    printf("Hello");
}

The body does not execute.

5. Can a `do-while` loop execute zero times?

No. The body executes once before the condition is checked.

do
{
    printf("Hello");
}
while (0);

Hello is still printed once.

6. When should I use `while` instead of `do-while`?

Use while when the program should check a condition before doing anything.

Use do-while when the operation should happen at least once, such as displaying a menu or asking for input.

7. Why does a `do-while` loop have a semicolon after `while`?

The semicolon is part of the syntax:

do
{
    // code
}
while (condition);

It marks the end of the do-while statement.

Written by Shubhranshu Shekhar, who has trained 20000+ students in coding.

Rishabh Kumar

Introduction

Q1. Print Numbers from 1 to 10 Using while

Problem Statement

C Program

Sample Output

Explanation

Concepts Covered

Q2. Print Numbers from 10 to 1

Problem Statement

C Program

Sample Output

Explanation

Concepts Covered

Q3. Find the Sum of Numbers from 1 to N

Problem Statement

C Program

Sample Output

Explanation

Concepts Covered

Q4. Count the Digits of a Number

Problem Statement

C Program

Sample Output

Explanation

Concepts Covered

Q5. Find the Sum of Digits

Problem Statement

C Program

Sample Output

Explanation

Concepts Covered

Q6. Reverse a Number

Problem Statement

C Program

Sample Output

Explanation

Concepts Covered

Q7. Check Whether a Number Is Palindrome

Problem Statement

C Program

Sample Output

Explanation

Concepts Covered

Q8. Print Multiplication Table Using while

Problem Statement

C Program

Sample Output

Explanation

Concepts Covered

Q9. Create a Simple Menu Using do-while

Problem Statement

C Program

Sample Output

Explanation

Concepts Covered

Q10. Keep Asking for a Positive Number Using do-while

Problem Statement

C Program

Sample Output

Explanation

Concepts Covered

Key Takeaways

FAQs

1. What is a while loop in C?

2. What is a do-while loop in C?

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

4. Can a while loop execute zero times?

5. Can a do-while loop execute zero times?

6. When should I use while instead of do-while?

7. Why does a do-while loop have a semicolon after while?

Related Posts

Q1. Print Numbers from 1 to 10 Using `while`

Q8. Print Multiplication Table Using `while`

Q9. Create a Simple Menu Using `do-while`

Q10. Keep Asking for a Positive Number Using `do-while`

1. What is a `while` loop in C?

2. What is a `do-while` loop in C?

3. What is the main difference between `while` and `do-while`?

4. Can a `while` loop execute zero times?

5. Can a `do-while` loop execute zero times?

6. When should I use `while` instead of `do-while`?

7. Why does a `do-while` loop have a semicolon after `while`?