素数

质数又称素数。指在一个大于1的自然数中，除了1和此整数自身外，不能被其他自然数(不包括0)整除的数。

#include <stdio.h>#include <math.h>#include <conio.h>int main(){int i,m;printf("please input a number,the input number must be an integer and larger than 1:\n");scanf("%d",&m);if (m<2)return -1;double num = (int)sqrt((double)m);for (i = 2;i<=num;i++)if (m%i==0)break;if (i>num){printf("is a prime number!");printf("\n%d",m);}elseprintf("is not a prime number!");getch();return 0;}

求整数区间内的素数：

#include "math.h"#include <stdio.h>#include <conio.h>void main(){int i,j,k,m,leap = 1;for (i = 11;i <= 100;i++){m = (int)sqrt((double)i);for (j = 2;j < m;j++)if (i%j == 0){leap = 0;break;}if (leap){printf("i = %d\n",i);}leap = 1;}getch();}

求区间内所有素数的平方根之和：

#include "math.h"#include <stdio.h>#include <stdlib.h>#include <conio.h>void main(){int i,j,k,m,leap = 1;double sum = 0;printf("请输入一个大于3的整数：\n");scanf("%d",&k);if(k <= 3) exit(0);for (i = 3;i <= k;i++){m = (int)sqrt((double)i);for (j = 2;j <= m;j++)if (i%j == 0){leap = 0;break;}if (leap){sum += sqrt((double)i);printf("i = %d\n",i);}leap = 1;}printf("sum = %f",sum);getch();}