C Exercises: Add repeatedly all digits of a given non-negative number until the result has only one digit

C Programming Mathematics: Exercise-12 with Solution

Write a C program to add repeatedly all digits of a given non-negative number until the result has only one digit.

Example:
Input: 48
Output: 2
Explanation: The formula is like: 4 + 8 = 12, 1 + 2 = 3.

Pictorial Presentation:

Sample Solution:

C Code:

#include <stdio.h>

static int addDigits(int num) {
        return num - (num - 1) / 9 * 9;
    }

int main(void)
{
    int n = 12;
    printf("\nInitial number is %d, Single digit number is %d.", n, addDigits(n));
    n = 47;
    printf("\n\nInitial number is %d, Single digit number is %d.", n, addDigits(n));
    return 0;
}

Sample Output:

Initial number is 12, Single digit number is 3.

Initial number is 47, Single digit number is 2.

Flowchart:

C Programming Code Editor:

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