Area and circumference in c++

include<iostream.h>
#include<conio.h>
#include<math.h>
void main()
{
const float pi=3.14159;
float radius,area,circum;
//read radius of a circle
cout<<"enter r"<<endl;
cin>>radius;
//compute area
area=pi*radius*radius;
cout<<"the area"<<area<<endl;
//comput circumference
circum=2*pi*radius;
cout<<"circum"<<circum<<endl;
getch();
}