C :

#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <time.h>
int main()
{
  //  freopen("in","r",stdin);
 //   freopen("out","w",stdout);
    int i1, i2, i3, i4, k, n;

    while(scanf("%d", &n)!=EOF){
	k = fabs(n);
	i1 = k / 1000;
	i2 = (k - i1 * 1000) / 100;
	i3 = (k - i1 * 1000 - i2 * 100) / 10;
	i4 = k % 10;

	printf("%d\n", i1+i2+i3+i4);
    }

  return 0;
}

C++ :

#include<stdio.h>
#include<math.h>
int main()
{
	int num,sum,a1,a2,a3,a4;
	while(scanf("%d",&num) != EOF)
	{
		num = fabs(num); 
		a1 = num/1000;
		a2 = (num - a1*1000)/100;
		a3 = (num - a1*1000 - a2*100)/10;
		a4 = num%10;
		sum = a1 + a2 + a3 + a4;
		printf("%d\n",sum);
	}
}