Program to draw a line using Bresenhams Line Algorithm (BLA) for lines with slopes positive and less than 1

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

 void show_screen( );

 void bresenham_line(const int,const int,const int,const int);


 int main( )
    {
       int driver=VGA;
       int mode=VGAHI;

       int x_1=0;
       int y_1=0;

       int x_2=0;
       int y_2=0;

       do
      {
         show_screen( );

         gotoxy(8,10);
         cout<<\"Coordinates of Point-I (x1,y1) :\";

         gotoxy(8,11);
         cout<<\"ÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ\";

         gotoxy(12,13);
         cout<<\"Enter the value of x1 = \";
         cin>>x_1;

         gotoxy(12,14);
         cout<<\"Enter the value of y1 = \";
         cin>>y_1;

         gotoxy(8,18);
         cout<<\"Coordinates of Point-II (x2,y2) :\";

         gotoxy(8,19);
         cout<<\"ÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ\";

         gotoxy(12,21);
         cout<<\"Enter the value of x2 = \";
         cin>>x_2;

         gotoxy(12,22);
         cout<<\"Enter the value of y2 = \";
         cin>>y_2;

         initgraph(&driver,&mode,\"..\\\\Bgi\");

         setcolor(15);
           bresenham_line(x_1,y_1,x_2,y_2);

         setcolor(15);
           outtextxy(110,460,\"Press <Enter> to continue or any other key to exit.\");

         int key=int(getch( ));

         if(key!=13)
        break;
      }
       while(1);

       return 0;
    }



 //--------------------------  bresenham_line( )  ------------------------//


 void bresenham_line(const int x_1,const int y_1,const int x_2,const int y_2)
    {
       int color=getcolor( );

       int x1=x_1;
       int y1=y_1;

       int x2=x_2;
       int y2=y_2;

       if(x_1>x_2)
      {
         x1=x_2;
         y1=y_2;

         x2=x_1;
         y2=y_1;
      }

       int dx=abs(x2-x1);
       int dy=abs(y2-y1);
       int two_dy=(2*dy);
       int two_dy_dx=(2*(dy-dx));
       int p=((2*dy)-dx);

       int x=x1;
       int y=y1;

       putpixel(x,y,color);

       while(x<x2)
      {
         x++;

         if(p<0)
        p+=two_dy;

         else
        {
           y--;
           p+=two_dy_dx;
        }

         putpixel(x,y,color);
      }
    }


 //--------------------------  show_screen( )  ---------------------------//


 void show_screen( )
    {
       restorecrtmode( );
       textmode(C4350);

       cprintf(\"\\n********************************************************************************\");
       cprintf(\"*************************-                              -***********************\");
       cprintf(\"*------------------------- \");

       textbackground(1);
       cprintf(\" Bresenham\'s Line Algorithm \");
       textbackground(8);

       cprintf(\" -----------------------*\");
       cprintf(\"*-***********************-                              -*********************-*\");
       cprintf(\"*-****************************************************************************-*\");

       for(int count=0;count<42;count++)
      cprintf(\"*-*                                                                          *-*\");

       gotoxy(1,46);
       cprintf(\"*-****************************************************************************-*\");
       cprintf(\"*------------------------------------------------------------------------------*\");
       cprintf(\"********************************************************************************\");

       gotoxy(8,40);
       cout<<\"Note :\";

       gotoxy(8,41);
       cout<<\"ÍÍÍÍÍÍ\";

       gotoxy(12,43);
       cout<<\"The slope of the line should be positive and less than 1.\";


       gotoxy(1,2);
    }