f0208.cpp

来自「C++程序设计教程（第二版）源代码 钱能编著」· C++ 代码 · 共 22 行

//=====================================
// f0208.cpp
// 判断一个整数是否素数的稍微优化版
//=====================================
#include<iostream>
#include<cmath>   // sqrt()
using namespace std;
//-------------------------------------
int main(){
  cout<<"please input a number: \n";
  int m;
  cin>>m;
  double sqrtm=sqrt(m*1.0);
  for(int i=2; i<=sqrtm; ++i)
    if(m%i==0){
      cout<<m<<" isn't a prime.\n";
      return 1;
    }
  cout<<m<<" is a prime.\n";
}//====================================