C Program to Reverse a Number Using Recursion

Here is a C program to reverse digits of a number using recursion. Reversing the digits of a number means reversing the sequence of digits in a number. After reversing, least significant digit will become most significant digit of number and most significant digit becomes least significant digit and so on.

Let the total number of digits in a number is N. So a digit at ith position from left will become ith digit from right or N-i+1th digit from left.

For Example

Befor reverse : 25346
After reverse : 64352

Algorithm to reverse a number using recursion
  • N%10 returns the last digit(least significant) of N. For Example : 354%10 = 4.

  • N/10 return the number after removing least significant digit of N(rightmost digit of N). For Example: 2345/10 = 234.

  • log10(N) + 1 returns the number of digits in N. log10(N) is logarithm of N with base 10. For Example: log10(2311) + 1 = 4.

  • Let getReversedNumber(N) is a function, which returns reverse of N. Then, we can use recursion to reverse the digits if a number using below mention recursive equation.
    • getReversedNumber(N) = (N%10)X pow(10, (log10(N/10) + 1)) + getReversedNumber(N/10)
For Example
  • getReversedNumber(8645) = lastDigitOf(8645) x power(10, numberOfDigits(864)) + getReversedNumber(864)
  • getReversedNumber(8645) = lastDigitOf(8645) x 1000 + getReversedNumber(864)
  • getReversedNumber(8645) = 5x1000 + getReversedNumber(864)
  • getReversedNumber(8645) = 5x1000 + 468
  • getReversedNumber(8645) = 5468

  • C program to reverse the digits of a number recursively

    This program first take an integer as input form user, then reverse it's digits using modulus(%), division(/), multiplication(*) and logarithmic function inside a recursive function. After reversing it prints the reversed number.

    #include <stdio.h>
    #include <math.h>
    int getReversedNumber(int number);
    int main(){
        int number, reverse = 0;
        printf("Enter a number\n");
        scanf("%d", &number);
        reverse = getReversedNumber(number);
        printf("Reversed number : %d\n", reverse);
        return 0;
    int getReversedNumber(int number){
        int lastDigit, numberOfDigits, sign = 1;
        if(number < 0){
            number = number * -1;
            sign = -1;
        if(number < 10)
            return number*sign;
        lastDigit = number % 10;
        number = number / 10;
        numberOfDigits = log10(number) + 1;
        return (lastDigit*pow(10,numberOfDigits) + 
    Enter a number
    Reversed number : 2456

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