Bresenham's line drawing Code

Question

I'm trying to draw a line in C language using Bresenham's algorithm.I'm using turbo C++ in dosbox for windows 7 to implement this code.While compiling i'm not getting any error but when i run the code the programs terminates after obtaining the 2 co-ordinates.Please Help..

the message on compiling is as follows..

the directories path is as follows

My code..

  # include <stdio.h>
  # include <conio.h>
  # include <graphics.h>

  void main()
  {
    int dx,dy,x,y,p,x1,y1,x2,y2;
    int gd,gm;

    clrscr();

    printf("\n\n\tEnter the co-ordinates of first point : ");
    scanf("%d %d",&x1,&y1);
    printf("\n\n\tEnter the co-ordinates of second point : ");
    scanf("%d %d",&x2,&y2);

    dx = (x2 - x1);
    dy = (y2 - y1);

    p = 2 * (dy) - (dx);

    x = x1;
    y = y1;

    detectgraph(&gd,&gm);
    initgraph(&gd,&gm,"e:\\tc\\bgi");
    putpixel(x,y,WHITE);

    while(x <= x2)
    {
      if(p < 0)
      {
        x=x+1;
        y=y;
        p = p + 2 * (dy);
      }
      else
      {
        x=x+1;
        y=y+1;
        p = p + 2 * (dy - dx);
     }
     putpixel(x,y,WHITE);
   }
   getch();
   closegraph();
}

Answer 1

This is a typical perfect point to start the debugger and go through the code step-by-step, watching any variables. If a debugger is unavailable, printf debugging to the console is a backup alternative.

A first tip is to check that these lines do not generate an error/exception:

  detectgraph(&gd,&gm);
  initgraph(&gd,&gm,"e:\\tc\\bgi");
  putpixel(x,y,WHITE);

Answer 2

Nice program. But, you haven't initialized any loop as well as lines coded in while-loop were partially incorrect. Here is my try:-

i = 1; // loop initialization
do {
    putpixel(x, y, 15);
    while(p >= 0) {
        y = y + 1;
        p = p - (2 * dx);
    }
    x = x + 1;
    p = p + (2 * dy);
    i = i + 1;
}
while(i <= dx);

Answer 3

OP should post input that was used.

The posted sample code does not work is x1 > x2 nor y1 > y2. This is one set of input that would stop the routine abruptly. To fix, the dx and dy should be based on the absolute value and the incremental x & y steps need to be independently +1 or -1.

An input of 3,4 instead of 3 4 (comma vs. whitespace) will also mess up the routine.

In the while loop, recommend if(p <= 0).

OP's "... code the programs terminates after obtaining the 2 co-ordinates." is not detailed enough, for of course the code should terminate sometime after obtaining the 2 co-ordinates. But OP does not detail where it terminates too early.

Answer 4

A way to rectify the problem is by changing the path in the initgraph function according to the address mentioned in the screenshot.

detectgraph(&gd,&gm);
initgraph(&gd,&gm,"C:\\TURBOC3\\bgi");
putpixel(x,y,WHITE);