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# C program to find sum of all digits until sum is not in single digit

This program is asked by **kalyani shevale** through comment on **18/12/2016**.

### Question

*
I want one program code *

input is an only integer value and output will be displayed only one digit in c

e g

input int a=8999

8+9+9+9=35

3+5=8

### Answer

Here, we are writing this code to calculate sum of all digits until sum is not in single digit in c programming language.

**For example:**

If number is 8999 the sum will be 8+9+9+9 = 35 = 3+5 = 8

This program is implementing by using recursion function, the function calculateDigits() is calling recursively until sum is not less than 10.

#include <stdio.h>
int calculateDigits(int num)
{
int sum=0;
while(num!=0)
{
sum+=(num%10);
num/=10;
}
if(sum>=10)
calculateDigits(sum);
else
return sum;
}
int main()
{
int n,sum;
printf("Enter any positive integer number: ");
scanf("%d",&n);
if(n<0)
{
printf("Invalid input!!!\n");
return -1;
}
sum=calculateDigits(n);
printf("Sum of digits is: %d\n",sum);
return 0;
}

### Output

First run:
Enter any positive integer number: 8999
Sum of digits is: 8
Second run:
Enter any positive integer number: 12345
Sum of digits is: 6