Program to find volume of cube, cylinder and rectangle

#include <iostream.h>
#include <conio.h>

//Declaration (Prototypes)
int volume (int);
double volume (double, int) ;
long volume (long, int, int) ;

int main( )
{
    cout << volume (10) <<endl;
    cout <<volume (2.5, 8) <<endl;
    cout <<volume (100L, 75, 15) <<endl;
    getch( );
    return 0;
}
int volume (int x)                 // volume of cube
{
           return (x*x*x);
}
double volume(double r, int h)              // volume of cylinder
{
           return (3.14519*r*r*h) ;
}
long volume(long l, int b, int h)           // volume of rectangular
{
           return (l*b*h);
}