#include <iostream>
using std::cout;
using std::cin;
using std::endl;

int grid[25][25];

void drawLine(int x1, int y1, int x2, int y2)
{
  // Draw pattern on bad input
  if ((x1 < 0 || x1 > 24) ||
      (y1 < 0 || y1 > 24) ||
      (x2 < 0 || x2 > 24) ||
      (y2 < 0 || x2 > 24)) {
    drawLine(0,0,24,0);
    drawLine(0,24,24,24);
    drawLine(0,0,0,24);
    drawLine(24,0,24,24);
    drawLine(0,12,24,12);
    drawLine(12,0,12,24);
    return;
  }

  int rise = y2 - y1;
  int run  = x2 - x1;

  grid[y1][x1] = 1;

  if (run > rise) {
    
    // slope less than 1
    // step along x axis

    int y = y1;
    int p = y1;
    
    while (x1 != x2) {
      x1++;
      
      y += rise;
      
      if ( (p + run - y) < 
	   (y - p) ) {
	p += run;
	y1++;
      } 
      
      grid[y1][x1] = 1;
    }
  } else {
    
    // slope greater than or equal to 1
    // step along y axis

    int x = x1;
    int p = x1;
    
    while (y1 != y2) {
      y1++;
      
      x += run;

      if ( (p + rise - x) < 
	   (x - p) ) {
	p += rise;
	x1++;
      } 
 
      grid[y1][x1] = 1;
    }
  }
}


void printGrid() 
{
  cout << "----------------------------------------------------" << endl;

  for (int i = 24; i >= 0 ; i--) {

    if (i < 10) 
      cout << " ";

    // y axis
    cout << i;

      for (int j = 0; j < 25; j++) {
	if (grid[i][j]) {
	  cout << "* ";
	} else {
	  cout << "  ";
	}
      }

      cout << endl;

  }

  cout << "----------------------------------------------------" << endl;

  cout << "                      1 1 1 1 1 1 1 1 1 1 2 2 2 2 2"<< endl;

  cout << "  ";

  // x axis
  for (int i = 0; i < 25; i++) {
    cout << i % 10 << " ";
  }

  cout << endl << endl;
}


void clearGrid() 
{
  for (int i = 0; i < 25; i++) {
    for (int j = 0; j < 25; j++) {
      grid[i][j] = 0;
    }
  }
}


int main()
{
  // Initialize grid
  clearGrid();


  // Test lines

  // m <= 1
  drawLine(0, 0, 24, 24);
  drawLine(0, 0, 24, 21);
  drawLine(0, 0, 24, 18);
  drawLine(0, 0, 24, 15);
  drawLine(0, 0, 24, 12);
  drawLine(0, 0, 24, 9);
  drawLine(0, 0, 24, 6);
  drawLine(0, 0, 24, 3);
  drawLine(0, 0, 24, 0);

  // m >= 1
  drawLine(0, 0,  0, 24);
  drawLine(0, 0,  3, 24);
  drawLine(0, 0,  6, 24);
  drawLine(0, 0,  9, 24);
  drawLine(0, 0, 12, 24);
  drawLine(0, 0, 15, 24);
  drawLine(0, 0, 18, 24);
  drawLine(0, 0, 21, 24);
  drawLine(0, 0, 24, 24);

  printGrid();


  // User-entered lines

  int x1;
  int y1;
  int x2;
  int y2;

  while (true) {
    cout << "Ctrl-c to quit" << endl;
    cout << "Each value should be between 0 and 24, inclusive, ";
    cout << "with x1 <= x2 and y1 <= y2" << endl;

    cout << "enter x1: "; cin >> x1;
    cout << "enter y1: "; cin >> y1;
    cout << "enter x2: "; cin >> x2;
    cout << "enter y2: "; cin >> y2;

    cout << x1 << " " << y1 << " " << x2 << " " << y2 << " " << endl;

    clearGrid();
    drawLine(x1, y1, x2, y2);
    cout << "(x1, y1) = " << "(" << x1 << ", " << y1 << ") \n" 
	 << "(x2, y2) = " << "(" << x2 << ", " << y2 << ") " << endl;
    printGrid();
  }

  return 0;
}