/* This program uses a class Line and a struct Point to calculate the
   intersection point between 2 lines.  
*/

#include<iostream.h>
#include<math.h>

bool equal(double,double);  // Tests to see if two double values are equal.

struct Point{                   // struct has the same syntax as class,
  public:                       // except there are no function members of 
    double x_coord, y_coord;    // a struct.  All the data members of a  
};                              // struct should be public.

class Line{
  private:
    double slope, intercept;
    Point intersect_pt;
  public:
    void get_line_data();
    void show_line_data();
    void calc_intersect_pt(Line);
};

void Line :: get_line_data () {
  cout << "Enter the slope and the y-intercept of the line: ";
  cin >> slope >> intercept;
}

void Line :: show_line_data () {
  cout << "Slope = " << slope << ", Intercept = " << intercept << ".\n";
}

void Line :: calc_intersect_pt (Line crossing_line){
  /* First handle the special cases where the 2 lines have the same slope. */ 
  if (equal(crossing_line.slope, slope)){
    if (equal(intercept, crossing_line.intercept))
      cout << "These two lines are identical." << endl;
    else
      cout << "These two lines are parallel." << endl;
  }
  /* This is the general case, when the 2 lines intersect in a point. */
  else{
    intersect_pt.x_coord = (crossing_line.intercept - intercept) /
      (slope - crossing_line.slope);
    intersect_pt.y_coord = slope * intersect_pt.x_coord + intercept;
    cout << "The intersection point is (" << intersect_pt.x_coord
	 << "," << intersect_pt.y_coord << ")." << endl;

    /* Notice that intersect_pt is a data member of the object which
       calls this function.  Then since intersect_pt is of type Point,
       which is a struct, we access its x coordinate by using 
       intersect_pt.x_coord  
    */
  }
}

void main() {

  Line line1, line2;

  line1.get_line_data();
  line2.get_line_data();

  line1.show_line_data();
  line2.show_line_data();

  line1.calc_intersect_pt (line2);
}

bool equal(double x, double y){
   
  double tolerance = 1e-10;

  return (fabs(x-y)<tolerance); /* Note that we return a logical expression
                                   for this bool type function.  
				*/
}