prime number(2.3.5.7.11.13.......)
 repeat input number from keyboard until number is 0;  
 check that number is prime number or not.
 If it is prime number,sum all of them
gaoshou , bangmang xia le !!!!!!!

#include<stdio.h>
#include<math.h>

int IsPrime(int n);

int main(void)
{
   int   a, s = 0;

   while (scanf("%d", &a) && a)
      if (IsPrime(a))
         s += a;
   printf("Sum = %d\n", s);
   return 0;
}

int IsPrime(int   n)
{
   int   i, k;

   k = sqrt(n);
   for (i = 2; i < k; i++)
      if (n % i == 0)
         return 0;
   return 1;
}

I'm not sure if the program is right.

楼上的 i<=k

呃不好意思，记不太清楚了

#include<stdio.h>
main()
{
    int i,k,n,sum=0;
    printf("Input number:i\n");
    scanf("%d",&i);
    while(i!=0) 
    {  printf("i=%3d\n",i);
       if (i>0&&i<=2) sum=sum+i;
       else
       { for(n=2;n<=i-1;n++)
       {
         
          k=i%n;
                 if(k==0) break; else sum=sum+i;
          
       }}
       scanf("%d",&i);
    }
    printf("sum=%d\n",sum);
}

hope that can help you