To find Prime or not

#include<iostream.h>
#include<conio.h>
void main()
{
 int n,a=0;
 clrscr();
 cout<<"Enter the no:";
 cin>>n;
 for(int i=1;i<=n;i++)
 {
  if(n%i==0)
   {
     a++;
   }
 }
 if(a==2)
  cout<<"It's a prime number";
 else
  cout<<"It's not a prime no";
 getch();
}