C++ PI,AREA,CIRCUMFERENCE

#include<iostream.h>
#include<conio.h>
#define PI 3.1416
void main(){
clrscr();
float a,area,volume;
cout<<"Enter #";
cin>>a;
area=4*PI*a*a;
volume=(4/3)*PI*a*a*a;
cout<<"\nsphere surface:"<<area;
cout<<"\nvolume of sphere:"<<volume;
getch();
}