// Gravitational field of a point earth. 
// Illustrates simple three dimensional
// plotting routines.

#include<iostream>
using namespace std;

const double km = 1000;		// Note this procedure! 
				// An alternate naming 
				// convention capitalizes 
				// all global constants

const double gravitationalConstant = 6.67e-11;
const double earthMass = 5.97e24;
const double earthRadius = 6380 * km;

const int matSize = 20;		// This MUST be declared a const int
				// to be used in the subsequent
				// type statements !

double gravitationalField (double aX, double aY) {
  return gravitationalConstant * earthMass / (aX * aX + aY * aY);
}

int main() {
  double position[matSize];	     // x and y coordinate space
  float offset = matSize / 2 - 0.5;  // Determines the starting 
                                     // point of the grid
             
  for (int loop = 0; loop < matSize; loop++) 
    position[loop] = 0.1 * earthRadius * (loop - offset);

  float x, y;
  for (int outerLoop = 0; outerLoop < matSize; outerLoop++) { 
    x = position[outerLoop];
    for (int innerLoop = 0; innerLoop < matSize; innerLoop++) {
      y = position[innerLoop];
      cout << x << " " << y << " " << gravitationalField(x,y) << endl;
    }
  }
}