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C Program to find the sum of digits of a number

Last updated on September 23, 2020

The following C program finds the sum of digits of a number.

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/************************************************
 * Program to find the sum of the digits of a number
*************************************************/

#include<stdio.h> // include stdio.h

int main()
{
    int n, remainder, sum = 0;

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

    while(n != 0)
    {
        remainder = n % 10;
        sum += remainder;
        n = n / 10;
    }

    printf("sum = %d", sum);

    return 0;
}

Expected Output: Run 1:

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2
Enter a number: 12345
sum = 15

Run 2:

1
2
Enter a number: 99999   
sum = 45

Try it now

How it works

The following table demonstrates the algorithm we used to find the sum of digits of the a given number:

Iteration remainder sum n
After 1st iteration remainder = 12345%10 = 5 sum = 0+5 = 5 n = 12345/10 = 1234
After 2nd iteration remainder = 1234%10 = 4 sum = 5+4 = 9 n = 1234/10 = 123
After 3rd iteration remainder = 123%10 = 3 sum = 9+3 = 12 n = 123/10 = 12
After 4th iteration remainder = 12%10 = 2 sum = 12+2 = 14 n = 12/10 = 1
After 5th iteration remainder = 1%10 = 1 sum = 14+1 = 15 n = 1/10 = 0

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