Convert decimal to binary c + +

#include<iostream.h>
#include<conio.h>
#include<math.h>
void main()
{
long int num,no=0,a=1,rem;
clrscr();
cout<<"\n Enter the decimal number:";
cin>>num;
while(num!=0)
{
rem=num%2;
no=no+rem*a;
num=num/2;
a=a*10;
}
cout<<"\n Binary is:"<<no;
getch();

}