#include <fstream.hfa>
#include <stdlib.hfa>

struct MR { double mass, radius; };

enum( MR ) Planet {
	//          mass (kg)  radius (km)
	MERCURY = { 0.330_E24, 2.4397_E6 },
	VENUS   = { 4.869_E24, 6.0518_E6 },
	EARTH   = { 5.976_E24, 6.3781_E6 },
	MOON    = { 7.346_E22, 1.7380_E6 }, // not a planet
	MARS    = { 0.642_E24, 3.3972_E6 },
	JUPITER = { 1898._E24, 71.492_E6 },
	SATURN  = { 568.8_E24, 60.268_E6 },
	URANUS  = { 86.86_E24, 25.559_E6 },
	NEPTUNE = { 102.4_E24, 24.746_E6 },
};

enum( double ) { G = 6.6743_E-11 }; // universal gravitational constant (m3 kg-1 s-2)

static double surfaceGravity( Planet p ) with( p ) {
	return G * mass / ( radius \ 2 ); // exponentiation
}
static double surfaceWeight( Planet p, double otherMass ) {
	return otherMass * surfaceGravity( p );
}

int main( int argc, char * argv[] ) {
	if ( argc != 2 ) exit | "Usage: " | argv[0] | "earth-weight";

	double earthWeight = convert( argv[1] );
	double earthMass = earthWeight / surfaceGravity( EARTH );

	Planet p = fromInt( prng( SizeE(Planet) ) ); // select a random orbiting body
//	Planet p = fromInt( prng( 9 ) ); // select a random orbiting body
	choose( p ) {
	  case MERCURY, VENUS, EARTH, MARS:
		sout | labelE( p ) | "is a rocky planet";
	  case JUPITER, SATURN, URANUS, NEPTUNE:
		sout | labelE( p ) | "is a gas-giant planet";
	  default:
		sout | labelE( p ) | "is not a planet";
	}

//	for ( Planet p = MERCURY; posE(p) <= posE(NEPTUNE); p = succ( p ) ) {
	for ( p; enum Planet ) {
		sout | "Your weight on" | (p == MOON ? "the" : "") | labelE(p)
//		sout | "Your weight on" | labelE(p)
			 | "is" | wd( 1,1, surfaceWeight( p, earthMass ) ) | "kg";
	}
}