C 質數檢查(Is Prime check )

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

int isPrime(int number)
{ 
     int i;
     for(i=2;i<number;i++)    // for(i=2;i<=((int)(sqrt(number)));i++)
     {
       if((number % i == 0 ))
         return number;                   
     }
     return -1;
}
int main()
{
  
     int number ; 
     int rval;
     printf("please input a number\n ");
     scanf("%d",&number);
     rval = isPrime(number);
     if(rval == -1)
       printf(" %d is a prime\n",number);
     else 
       printf(" %d is not a prime\n",number);
     system("pause");  
}