C program to implement DDA algorithm

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

#define round(a) ((int) (a+0.5))
void lineDDA(int xa,int ya,int xb,int yb);
int main(void)
{
   /* request auto detection */
   int gdriver = DETECT, gmode, errorcode;
   int xa,ya,xb,yb;

   /* initialize graphics and local variables */
   initgraph(&gdriver, &gmode, "..\\bgi");

   lineDDA(0,0,640,480);
   lineDDA(640,0,0,480);
   lineDDA(320,0,320,480);
   lineDDA(0,240,640,240);

   getch();
   closegraph();
  
}

void lineDDA(int xa,int ya,int xb,int yb)
{
 int dx=xb-xa,dy=yb-ya,steps,k;
 float xinc,yinc,x=xa,y=ya;

 if(abs(dx)>abs(dy))
  steps=abs(dx);
 else
 steps=abs(dy);

 xinc=dx/(float) steps;
 yinc=dy/(float) steps;
 putpixel(round(x),round(y),5);
 for(k=0;k<steps;k++)
 {       x+=xinc;
  y+=yinc;
  putpixel(round(x),round(y),2);
 }
}