#include<iostream.h>
#include<conio.h>
#include<stdlib.h>
#include<dos.h>
#include<math.h>
#include<graphics.h>

typedef struct coordinate {
  int x, y;
  char code[4];
}
PT;
void drawwindow();
void drawline(PT p1, PT p2, int cl);
PT setcode(PT p);
int visibility(PT p1, PT p2);
PT resetendpt(PT p1, PT p2);
main() {
  int gd = DETECT, gm, v;
  PT p1, p2, ptemp;
  initgraph( & gd, & gm, "c:\\tc\\bgi ");
  cleardevice();
  cout << "\n\n\t\tENTER END-POINT 1 (x,y): ";
  cin >> p1.x >> p1.y;
  cout << "\n\n\t\tENTER END-POINT 2 (x,y): ";
  cin >> p2.x >> p2.y;
  cleardevice();
  drawwindow();
  getch();
  drawline(p1, p2, 15);
  getch();
  p1 = setcode(p1);
  p2 = setcode(p2);
  v = visibility(p1, p2);
  switch (v) {
  case 0:
    cleardevice();
    drawwindow();
    drawline(p1, p2, 15);
    break;
  case 1:
    cleardevice();
    drawwindow();
    break;
  case 2:
    cleardevice();
    p1 = resetendpt(p1, p2);
    p2 = resetendpt(p2, p1);
    drawwindow();
    drawline(p1, p2, 15);
    break;
  }
  getch();
  closegraph();
  return (0);
}
void drawwindow() {
  setcolor(RED);
  line(150, 100, 450, 100);
  line(450, 100, 450, 350);
  line(450, 350, 150, 350);
  line(150, 350, 150, 100);
}
void drawline(PT p1, PT p2, int cl) {
    setcolor(cl);
    line(p1.x, p1.y, p2.x, p2.y);
    PT setcode(PT p) {
      PT ptemp;
      if (p.y < 100)
        ptemp.code[0] = '1';
      else
        ptemp.code[0] = '0';
      if (p.y > 350)
        ptemp.code[1] = '1';
      else
        ptemp.code[1] = '0';
      if (p.x > 450)
        ptemp.code[2] = '1';
      else
        ptemp.code[2] = '0';
      if (p.x < 150)
        ptemp.code[3] = '1';
      else
        ptemp.code[3] = '0';
      ptemp.x = p.x;
      ptemp.y = p.y;
      return (ptemp);
    }
    int visibility(PT p1, PT p2) {
      int i, flag = 0;
      for (i = 0; i < 4; i++) {
        if ((p1.code[i] != '0') || (p2.code[i] != '0'))
          flag = 1;
      }
      if (flag == 0)
        return (0);
      for (i = 0; i < 4; i++) {
        if ((p1.code[i] == p2.code[i]) && (p1.code[i] == '1'))
          flag = 0;
      }
      if (flag == 0)
        return (1);
      return (2);
    }
    PT resetendpt(PT p1, PT p2) {
      PT temp;
      int x, y, i;
      float m, k;
      if (p1.code[3] == '1')
        x = 150;
      if (p1.code[2] == '1')
        x = 450;
      if ((p1.code[3] == '1') || (p1.code[2] == '1')) {
        m = (float)(p2.y - p1.y) / (p2.x - p1.x);
        k = (p1.y + (m * (x - p1.x)));
        temp.y = k;
        temp.x = x;
        for (i = 0; i < 4; i++)
          temp.code[i] = p1.code[i];
        if (temp.y <= 350 && temp.y >= 100)
          return (temp);
      }
      if (p1.code[0] == '1')
        y = 100;
      if (p1.code[1] == '1')
        y = 350;
      if ((p1.code[0] == '1') || (p1.code[1] == '1')) {
        m = (float)(p2.y - p1.y) / (p2.x - p1.x);
        k = (float) p1.x + (float)(y - p1.y) / m;
        temp.x = k;
        temp.y = y;
        for (i = 0; i < 4; i++)
          temp.code[i] = p1.code[i];
        return (temp);
      } else
        return (p1);
    }