#include <stdafx.h>
#include "iostream"
#include <cmath>
#include <stdlib.h>
using namespace std;
void main(){
    cout<<"please input a number.\n";
    int m;
    double n;
    cin>>m;
    n=sqrt(m*1.0);
    for(int i=1;i<=n;++i)
        if(m%i==0){
            cout<<m<<" isn't a prime.\n ";
             }
        else cout<<m<<"  is a prime.\n";
        system("pause");
        }
搞不懂。。会出现这样的结果
please input a number.
4
4  isn't a prime.
 4 isn't a prime.

输入5时有不一样了

please input a number.
5
5 isn't a prime.
 5 is a prime.

for(int i=1;i<=n;++i)
        
        if(m%i==0)
            
    {    cout<<m<<" isn't a prime.\n ";break;
            
        }
        else     
    cout<<m<<"  is a prime.\n";
那我把后天改成这样，，为什么不会多次输出is