C Programs

Share with a Friend

Functions in C

Recursive Function to print sum of digits of a number

C Program: Recursive Function to print sum of digits of a number

#include <stdio.h>
 
// Function declaration
int sumOfDigits(int num);
 
int main() {
    int number;
 
    // Input number
    printf("Enter a number: ");
    scanf("%d", &number);
 
    // Function call and display result
    printf("Sum of digits of %d = %d\n", number, sumOfDigits(number));
 
    return 0;
}
 
// Recursive function to calculate sum of digits
int sumOfDigits(int num) {
    if (num == 0)
        return 0;  // Base condition
    return (num % 10) + sumOfDigits(num / 10);
}
 

 
OUTPUT 1 :
Enter a number: 1234
Sum of digits of 1234 = 10

OUTPUT 2 :
Enter a number: 987
Sum of digits of 987 = 24

Explanation

1. Recursive Concept
   • Every time the function is called, it separates the last digit using num % 10.
   • Adds that digit to the result of sumOfDigits(num / 10).
   • When num becomes 0, recursion stops (base case).
2. Flow Example (for 1234)

           sumOfDigits(1234)

           = 4 + sumOfDigits(123)

           = 4 + 3 + sumOfDigits(12)

           = 4 + 3 + 2 + sumOfDigits(1)

           = 4 + 3 + 2 + 1 + sumOfDigits(0)

           = 10