C語言函數實現判斷一個數是不是素數

#include <stdio.h>
#include <math.h>
#define YES 1
#define NO 0
void main()
{
 int n;
 int Prime_num(int n);//聲明Prime_num函數
  
 printf("please enter a number:");
 scanf("%d",&n);//輸入要判斷的的數
 Prime_num(n);//調用Prime_num函數
 if(Prime_num(n)==YES)
  printf("%d is a prime number\n",n);
 else
  printf("%d is not a prime number\n",n);
}
int Prime_num(int n)//定義Prime_num函數
{
 int i;
 if(n==2)
  return YES;
 else
  if(n<2||n%2==0)
   return NO;
  else
  {
   for(i=3;i<=sqrt(n);i+=2)
   {
    if(n%i==0)
     return NO;
   }
  }
  return YES;
}