范围求素数

一只音爆

芜湖~

#include <bits/stdc++.h>

using namespace std ;
//万能头+经典引入 

int main(){
	long long n , sum=1;
	
	//定义灵魂量量
	
	cin>>n;

	cout<<2<<" ";
	for( int i = 3 ; i < n ; i ++){
		//轮回 
		int a=1;
		for ( int j = 2 ; j < i ; j ++){
			if ( i%j == 0) {
				a=0;
				break;		
			}
			
		}
		
		if ( a){
			cout<<i<<" ";
			sum ++ ;
		}
		
	}
	cout<<"\n";
	cout << sum ;
	
	
}

屈老师

#include <iostream>
#include <vector>
using namespace std;

int main() {
    int n;
    cin >> n;
    vector<int> a(n + 1, 1); 

    a[0] = a[1] = 0;
    for (int i = 2; i * i <= n; i++) {
        if (a[i]) { 
            for (int j = i * i; j <= n; j += i) {
                a[j] = 0;
            }
        }
    }

    for (int i = 2; i <= n; i++) {
        if (a[i]) {
            cout << i << " ";
        }
    }
    cout << endl;

    return 0;
}