Prime no program in c++

#include<stdio.h>
#include<conio.h>
#include<iostream.h>
void main()
{
 int num,i,num1;
 cout<<"enter no=";
 cin>>num;
 i=2;
 num1=num-1;
 while(i<=num1)
 {
  if(num%i==0)
  {
cout<<"not a prime no\n";
break;
}
i++;
  }
  if(i==num)
cout<<"prim no\n";
getch();
 }