• C Program to Reverse a Number

    Welcome to this comprehensive blog post on how to reverse a number using a function in the C programming language. Whether you’re new to programming or have some experience, this post will guide you through the process step by step.


    Reversing a number involves changing the order of its digits. For example, reversing the number 123 would give us 321. Understanding how to reverse a number is not only a fundamental concept in programming but also a useful skill to have. It can be applied in various scenarios, such as checking for palindromes or manipulating numerical data.

    In this blog post, we will explore a C program that reverses a given number using a function. We’ll discuss the logic behind the program, the implementation details, and provide a working example.

    Let’s dive in!

    Understanding the Logic

    To reverse a number, we need to extract its individual digits and construct a new number by reversing their order. We can achieve this by using the modulo (%) and division (/) operators.

    Here’s the general logic for reversing a number:

    1. Initialize a new variable to store the reversed number.

    2. Extract the last digit of the original number using the modulo operator (%). This can be done by taking the original number modulo 10.

    3. Append the extracted digit to the reversed number by multiplying it by 10 and adding it to the reversed number.

    4. Remove the last digit from the original number using integer division (/). This can be done by dividing the original number by 10.

    5. Repeat steps 2-4 until all digits have been processed.

    6. The final value of the reversed number will be the desired result.

    Implementing the C Program

    Now that we understand the logic, let’s implement the C program to reverse a number using a function. First, we need to define the function prototype.

    https://ccodelearner.com/c-examples/reverse-number/#include <stdio.h> int reverseNumber(int num); // Function prototype

    The function reverseNumber takes an integer num as an argument and returns an integer representing the reversed number.

    Next, we can define the function itself.

    int reverseNumber(int num) {
        int reversedNum = 0;
        while(num != 0) {
            int digit = num % 10;
            reversedNum = (reversedNum * 10) + digit;
            num /= 10;
        return reversedNum;

    Inside the function, we declare a variable reversedNum and initialize it to 0. This variable will store the reversed number.

    We then enter a while loop that continues until num becomes 0. In each iteration, we extract the last digit of num using the modulo operator and store it in the digit variable. We then update reversedNum by multiplying it by 10 and adding the extracted digit. Finally, we remove the last digit from num by dividing it by 10.

    Once the while loop finishes, we return the reversedNum as the result.

    Writing the Main Function

    To test our reverseNumber function, we need to write a main function that takes user input and calls the function.

    int main() {
        int num;
        printf("Enter a number to reverse: ");
        scanf("%d", &num);
        int reversed = reverseNumber(num);
        printf("The reversed number is: %d\n", reversed);
        return 0;

    In the main function, we declare an integer variable num to store the user input. We prompt the user to enter a number and read it using the scanf function.

    Next, we call the reverseNumber function with num as the argument and store the result in the reversed variable.

    Finally, we print the reversed number using printf and return 0 to indicate successful execution of the program.

    Running the Program

    To run the program, we need to compile and execute it. Save the code with a .c extension, such as reverse_number.c, and then open a terminal or command prompt.

    Use the gcc compiler to compile the code:

    gcc reverse_number.c -o reverse_number

    This command will generate an executable file named reverse_number (or any name you specified). Execute the program by running:


    You will be prompted to enter a number. Once you provide the input, the program will display the reversed number.

    Example Run

    Let’s run our program with an example. Suppose we want to reverse the number 1234.

    https://ccodelearner.com/c-examples/reverse-number/Enter a number to reverse: 1234 The reversed number is: 4321

    As we can see, our program successfully reversed the number 1234 and displayed the result as 4321.


    Through this blog post, Finally, we have explored how to reverse a number using a function in the C programming language. We learned the logic behind the process, implemented a function to reverse a given number, and tested it with a main function.

    Reversing a number is a useful skill to have in programming, and it can be applied in various scenarios. By grasping the concept and following the steps outlined in this blog post, you can easily reverse a number using a function in C.

    Feel free to experiment and further enhance your program to handle negative numbers, floating-point numbers, or larger numbers. Exercising your newfound knowledge will solidify your understanding and improve your programming skills.

    Happy coding!