1 #include <stdio.h> 2 #include <stdlib.h> 3 #include <string.h> 4 #include <math.h> 5 int main() 6 { 7     int prime(int); 8     int prime2(int); 9     int n;10     printf("input a number: ");11     scanf("%d",&n);12     if(prime2(n))13         printf("%d is a prime.\n",n);14     else printf("%d is not a prime.\n",n);15         system("pause");16     return 0;17 }18 int prime(int n){//普通法19     int flag=1,i;20     for(i=2;i<n/2 &&flag ==1;i++){21         if(n%i==0)22             flag=0;23     }24     return (flag);25 }26 int prime2(int n){//初等数论法27     int flag=1,i;28     for(i=2;i<sqrt(n) &&flag ==1;i++){29         if(n%i==0)30             flag=0;31     }32     return (flag);33 }