找素数

找出3~1000中的全部素数。

#include<math.h>

void main()

{ 

        unsigned int i,j,count,flag;

        count=0;

        for(i=3;i<=1000;i++)

         { 

                  flag=0;

                  for(j=2;j<=sqrt(i);j++)  /*使用该循环结束表达式j<=sqrt(i)可以减少循环次数，具体理解见附图

                  {

                             if(i%j==0)

                             {flag=1;break;}

                   }

                   if(flag==0)

                   {

                             printf(“%4d”,i);count++;

                             if(count%8==0) printf(“\n”);

                     }

            }

}