> #include<stdio.h>
> main()
> {
>      double sum;
>      unsigned long i,k,n;
>      scanf("%ld %ld",&n,&k);
>      while(n!=0)
>      {  
>          if(k>n/2) k=n-k;
>          sum=n/k; 
> 
>          for(i=1;i<k;i++)
>           { sum=sum/(k-i);
>             sum=sum*(n-i);
>           } 
> 
>          printf("%.0f\n",sum);
>          scanf("%ld %ld",&n,&k);       
>      }
> }

你这直接就有问题.先要保证整除.