#include<stdio.h>intmain(){
int i, n;printf("please input a number:");scanf("%d",&n);for(i =2; i < n ; i++){
if(n%i ==0)break;}if(n <=1)printf("This is not a prime\n");//n<=1的数当然是非素数elseif(i < n)printf("This is not a prime.\n");elseprintf("This is a prime.\n");return0;}
求100到200间的全部素数
#include<stdio.h>intmain(){
int i, j, k;for(i =101; i <201;i++){
k =1;for(j =2; j <i;j++){
if(i%j ==0){
k =0;break;}}if(k ==1)printf("%d \n", i);}return0;}
方法二:判断n是否能被2~√n间的整数整除
#include<stdio.h>#include<math.h>intmain(){
int n,i;double k;printf("please input a number:");scanf("%d",&n);
k =sqrt(n);for(i =2; i <= k;i++){
if(n%i