// Sample program for CS149.     v. 10/6/00
//   
//
// Program determines whether or not 4 pts define a parallelgoram.
//
//  To make things simplier, we assume points are given in
//    clockwise order, so we know which slopes to compare.

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

int main()
{
      //  Define and initialize variables.
	double x1, y1, x2, y2, x3, y3, x4, y4,
	slope_1, slope_2, slope_3, slope_4;

      // Define points.
        x1 = 0; y1 = 0;
        x2 = 4; y2 = 0;
        x3 = 4; y3 = 2;
        x4 = 0, y4 = 2;

      // Compute slopes.
	slope_1 = (y2-y1)/(x2-x1);
	slope_2 = (y3-y2)/(x3-x2);
	slope_3 = (y4-y3)/(x4-x3);
	slope_4 = (y4-y1)/(x4-x1);

      // Check for equal slopes of opposite sides.
        if ( (slope_1 == slope_3 ) && (slope_2 == slope_4 ) )
	   cout << "This is a parallelogram." << endl;
        else
           cout << "This is not a parallelogram. << endl;

      // Define points.
        x1 = 0; y1 = 0;
        x2 = 5; y2 = 0;
        x3 = 4; y3 = 2;
        x4 = 0, y4 = 2;

      // Compute slopes.
		slope_1 = (y2-y1)/(x2-x1);
		slope_2 = (y3-y2)/(x3-x2);
		slope_3 = (y4-y3)/(x4-x3);
		slope_4 = (y4-y1)/(x4-x1);

      // Check for equal slopes of opposite sides.
        if ( (slope_1 == slope_3 ) && (slope_2 == slope_4 ) )
	  cout << "This is a paral." << endl;
        else
	  cout << "This is not a rectangle." << endl;

      // Define points.
        x1 = 1; y1 = 0;
        x2 = 2; y2 = 1;
        x3 = 1; y3 = 2;
        x4 = 0, y4 = 1;

      // Compute slopes.
	slope_1 = (y2-y1)/(x2-x1);
	slope_2 = (y3-y2)/(x3-x2);
	slope_3 = (y4-y3)/(x4-x3);
	slope_4 = (y4-y1)/(x4-x1);

      // Check for equal slopes of opposite sides.
        if ( (slope_1 == slope_3 ) && (slope_2 == slope_4 ) )
	  cout << "This is a rectangle" << endl;
        else
	  cout << "This is not a rectangle." << endl;

	// Exit program.
	  return EXIT_SUCCESS;
}