C Exercises: Find the sum of digits of a number

Last update on March 20 2025 12:37:25 (UTC/GMT +8 hours)

6. Sum of Digits Recursion Variants

Write a program in C to find the sum of digits of a number using recursion.

Pictorial Presentation:

C Exercises: Find the sum of digits of a number

Sample Solution:

C Code:

#include <stdio.h>
 
int DigitSum(int num);
 
int main()
{
    int n1, sum;
	printf("\n\n Recursion : Find the sum of digits of a number :\n");
	printf("-----------------------------------------------------\n");     
    printf(" Input any number to find sum of digits: ");
    scanf("%d", &n1);
     
    sum = DigitSum(n1);//call the function for calculation
     
    printf(" The Sum of digits of %d = %d\n\n", n1, sum);
     
    return 0;
}

int DigitSum(int n1)
{
    if(n1 == 0)
        return 0;
         
    return ((n1 % 10) + DigitSum(n1 / 10));//calling the function DigitSum itself
}

Sample Output:

 Recursion : Find the sum of digits of a number :                                                             
-----------------------------------------------------                                                         
 Input any number to find sum of digits: 25                                                                   
 The Sum of digits of 25 = 7

Explanation:

int DigitSum(int n1)
{
    if(n1 == 0)
        return 0;
         
    return ((n1 % 10) + DigitSum(n1 / 10));//calling the function DigitSum itself
}

The function ‘DigitSum()’ takes an integer ‘n1’ as input and calculates the sum of its digits recursively.

The function first checks if the input n1 is equal to 0. If it is, then the function returns 0 as the sum of digits for an empty number is 0.

If the input n1 is not equal to 0, then the function calculates the remainder of the number divided by 10 (which gives the last digit of the number) and adds it to the sum of the remaining digits obtained by calling DigitSum() recursively with the number divided by 10 (which removes the last digit).

The function keeps calling itself recursively until the number becomes 0, at which point the sum of all the digits is returned.

Time complexity and space complexity:

The time complexity of the function is O(log n) where n is the given number.

The space complexity of the function is O(log n) due to the recursive calls.

Flowchart:

For more Practice: Solve these Related Problems:

Write a C program to multiply all the digits of a given number using recursion.
Write a C program to compute the digital root (repeated sum of digits) of a number recursively.
Write a C program to calculate the sum of the squares of the digits of a number using recursion.
Write a C program to recursively compute both the sum and product of the digits of a number.

C Programming Code Editor:

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