C++ 求1到100所有质数共有几个

#includeusing namespace std#define N 100void main() { int i,j,b,n; n=0; for ( i=1;i<N;i++ ) { b=1; for ( j=2;j<=i/2;j++ ) if ( i%j==0 ) { b=0;break; } if ( b ) n++; } cout<<n<<endl;}