# 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.

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**Previous:** Write a C program to count the total number of digit 1 appearing in all positive integers less than or equal to a given integer n.

**Next:** Write a C programming to check if a given integer is a power of three.

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