C Exercise Example 84
100 cases of classic C language
Title: always an even number can be expressed as the sum of two prime numbers.
Program Analysis: I went to,what is this subject, I want to prove this problem? I really do not know how to prove. Then put an even number into two prime numbers it.
Source Code:
// Created by www.w3big.com on 15/11/9.
// Copyright © 2015年 本教程. All rights reserved.
//
#include<stdio.h>
#include<stdlib.h>
int Isprimer(unsigned int n);
int main()
{
unsigned int n,i;
do{
printf("请输入一个偶数:\n");
scanf("%d",&n);
}while(n%2!=0);
for(i=1;i<n;i++)
if(Isprimer(i)&&Isprimer(n-i))
break;
printf("偶数%d可以分解成%d和%d两个素数的和\n",n,i,n-i);
return 0;
}
int Isprimer(unsigned int n)
{
int i;
if(n<4)return 1;
else if(n%2==0)return 0;
else
for(i=3;i<sqrt(n)+1;i++)
if(n%i==0)return 0;
return 1;
}
Run the above example output is:
请输入一个偶数: 4 偶数4可以分解成1和3两个素数的和