This is written in c using functins, hope it helps:
#include <stdio.h>
int add(int x,int y,int z);
int main()
{
int x,y,z,sum;
printf("Enter 3 no's: ");
scanf("%d %d %d", &x,&y,&z);
sum=add(x,y,z);
printf("Addition of +ve no's is:%d",sum);
return 0;
}
int add(int x,int y,int z)
{
int sum,res;
if(x>0)
sum+=x;
if(y>0)
sum+=y;
if(z>0)
sum+=z;
return sum;
}