C Program to Find Sum of Digit of Number Until it Reduces to Single Digit

In this C program, we are going to find sum of digit of a given number until it reduces to single digit. For Example, if 9999974 is given number then while finding sum of digit at first step we get 56 i.e. 9+9+9+9+9+7+4 = 56, similarly 56 is two digit number we again find sum of digit i.e. 5+6=11 and 11 is again two digit we find sum i.e. 1+1=2. And finally we get single digit i.e. 2 and then we stop this process.

Program

#include<stdio.h>
#include<conio.h>

int main()
{
	 long int number, sum, step=1, rem;
	 clrscr();
	 
	 printf("Enter number: ");
	 scanf("%ld", &number);
	 
	 do
	 {
		  sum = 0;
		  while(number!=0)
		  {
			   rem = number%10;
			   sum = sum + rem;
			   number = number/10;
		  }
		  
		  printf("Step-%ld Sum = %ld\n", step, sum);
		  number = sum;
		  step = step+1;
		  
	 }while(number>9);
	 
	 getch();
	 return(0);
}

Output of above program :

Run 1:
--------------
Enter number: 9999974 ↲
Step-1 Sum = 56
Step-2 Sum = 11
Step-3 Sum = 2

Run 2:
--------------
Enter number: 8 ↲
Step-1 Sum = 8

Note: ↲ indicates ENTER is pressed.