Program using Bresenham's line drawing algorithm ( all quadrants)

/* This program will draw x- y coordinate system and will draw lines in all quadrants using   Bresenham's line drawing algorithm  */

#include<graphics.h>
#include<conio.h>
#include<stdio.h>
void main()
{
int gd=DETECT,gm;
int i,xmid,ymid,x1,y1,x2,y2,x,y,dy,dx,p,gap=50,temp;
float m;
char str[3];
clrscr();
initgraph(&gd,&gm,"..\\bgi");

printf("Enter first co-ords of line\n");
scanf("%d",&x1);
scanf("%d",&y1);
printf("Enter second co-ords of line\n");
scanf("%d",&x2);
scanf("%d",&y2);
if (y1>y2)    // needed for -ve slope to work
{temp=x1;
x1=x2;
x2=temp;
temp=y1;
y1=y2;
y2=temp;
}
dy=abs(y2-y1);
dx=abs(x2-x1);
m=(float)(dy)/(dx);
dy=abs(dy);
dx=abs(dx);
xmid= getmaxx()/2;
ymid =getmaxy()/2;
x2=x2+xmid;
y2=ymid-y2;
x=x1;y=y1;
if(m>1.0)
{
x=y1;
y=x1;
}


line(5,ymid,getmaxx()-5,ymid);
line(xmid+3,5,xmid+3,getmaxy()-5);

for( i= xmid+gap;i<getmaxx()-5;i=i+gap)
{
outtextxy(i,ymid-3,"|");
itoa(i-xmid,str,10);
outtextxy(i,ymid+3,str);
}
for( i= ymid-gap;i>5;i=i-gap)
{
outtextxy(xmid,i,"-");
itoa(ymid-i,str,10);
outtextxy(xmid+5,i,str);

}
for( i= xmid-gap;i>5;i=i-gap)
{
outtextxy(i,ymid-3,"|");
itoa(-(xmid-i),str,10);
outtextxy(i-6,ymid+3,str);

}
for( i= ymid+gap;i<getmaxy()-5;i=i+gap)
{
outtextxy(xmid,i,"-");
itoa(-(i-ymid),str,10);
outtextxy(xmid+8,i,str);
}

x=x+xmid;
y=ymid -y;
p=2*dy-dx;
while(x<x2)
{
if(p>=0)
{
putpixel(x,y,5);

y=y-1;
p=p+2*dy-2*dx;
}
else
{
putpixel(x,y,5);
p=p+2*dy;
}
x=x+1;
}
getch();
closegraph();
}