Reverse a Number in C: Practice Questions Using While, Do-While, and For Loop

Reversing a number is a classic problem in programming that tests your logical thinking and understanding of loops. Whether you’re a fresher or a new learner diving into C programming, this is a great way to enhance your skills in handling loops like while, do-while, and for.

In this post, we’ll provide practice questions to reverse a number using all three types of loops in C. These exercises will solidify your understanding of iteration and logic, helping you ace interviews and coding challenges.

---

Understanding the Problem

Reversing a number means rearranging its digits in reverse order. For example:

• Input: 1234
• Output: 4321

To achieve this, we can:

1. Extract the last digit using the modulus operator (%).
2. Append it to the reversed number.
3. Remove the last digit using integer division (/).

---

Reversing a Number Using While Loop

Code Example 1: Reverse a Number Using While Loop

#include <stdio.h>

int main() {
    int num, reverse = 0, remainder;

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

    while (num != 0) {
        remainder = num % 10;
        reverse = reverse * 10 + remainder;
        num /= 10;
    }

    printf("Reversed Number: %d\n", reverse);
    return 0;
}

Reversing a Number Using Do-While Loop

Code Example 2: Reverse a Number Using Do-While Loop

#include <stdio.h>

int main() {
    int num, reverse = 0, remainder;

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

    do {
        remainder = num % 10;
        reverse = reverse * 10 + remainder;
        num /= 10;
    } while (num != 0);

    printf("Reversed Number: %d\n", reverse);
    return 0;
}

Reversing a Number Using For Loop

Code Example 3: Reverse a Number Using For Loop

#include <stdio.h>

int main() {
    int num, reverse = 0, remainder;

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

    for (; num != 0; num /= 10) {
        remainder = num % 10;
        reverse = reverse * 10 + remainder;
    }

    printf("Reversed Number: %d\n", reverse);
    return 0;
}

Practice Questions

1. Modify the code to handle negative numbers.
2. Write a program to reverse multiple numbers entered by the user.
3. Create a function to reverse a number and call it from the main function.
4. Implement the reversal logic for floating-point numbers.
5. Write a program to check if a number is a palindrome (same forward and backward).

---

Pro Tips for Beginners

1. Understand the logic: Focus on extracting digits and forming the reversed number.
2. Practice all loop types: Each loop has its use case, so try implementing the logic with different loops.
3. Debug with print statements: Use printf to print intermediate results and understand the flow.
4. Think of edge cases: Test your program with inputs like 0, 1000, and negative numbers.

---

Conclusion

Mastering loops and basic logic like reversing a number is crucial for any beginner in C programming. These examples and practice questions will help you build confidence and improve your coding skills. Keep experimenting, and don’t hesitate to apply similar logic to other problems!