HDU 2161Primes（判断是否是素数）

Primes

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Description

Write a program to read in a list of integers and determine whether or not each number is prime. A number, n, is prime if its only divisors are 1 and n. For this problem, the numbers 1 and 2 are not considered primes.

Input

Each input line contains a single integer. The list of integers is terminated with a number<= 0. You may assume that the input contains at most 250 numbers and each number is less than or equal to 16000.

Output

The output should consists of one line for every number, where each line first lists the problem number, followed by a colon and space, followed by "yes" or "no".

Sample Input

1
2
3
4
5
17
0 

Sample Output

1: no
2: no
3: yes
4: no
5: yes
6: yes 

题意：给出一个数，不是很大的数，问是否是素数

思路：暴力法即可。

<span style="font-size:18px;">#include <cstdio>
#include <iostream>
#include <cstring>
#include <cmath>
#include <string>
#include <algorithm>
#include <queue>
#include <stack>
using namespace std;

const double PI = acos(-1.0);
const double e = 2.718281828459;
const double eps = 1e-8;

int IsPrime(int n)
{
    if(n==1 || n==2)
        return 0;
    if(n%2 == 0)
        return 0;
    for(int i = 3; i*i <= n; i += 2)
        if(n%i == 0)
            return 0;
    return 1;
}

int main()
{
    //freopen("in.txt", "r", stdin);
    //freopen("out.txt", "w", stdout);
    int n;
    int num = 1;
    while(scanf("%d", &n)!=EOF)
    {
        if(n <= 0)  // 此题的最大坑，没有之一
            break;
        printf("%d: ", num++);
        if(IsPrime(n))
            printf("yes\n");
        else
            printf("no\n");
    }
    return 0;
}

</span>