DDA (Digital differential analyzer) Line Drawing Algorithm

/* compiler- Turbo c++ author- Mangilal Sharma =================================

DDA (Digital differential analyzer) Line Drawing Algorithm========================*/ 

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

void main()
{

    int gd = DETECT, gm = DETECT, s, dx, dy, m, x1, y1, x2, y2;
    float xi, yi, x, y;

    clrscr();

    printf("Enter the sarting point x1 & y1\n");
    scanf("%d%d", &x1, &y1);

    printf("Enter the end point x2 & y2\n");
    scanf("%d%d", &x2, &y2);

    initgraph(&gd, &gm, "");
    cleardevice();

    dx = x2 - x1;
    dy = y2 - y1;

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

    xi = dx / (float) s;
    yi = dy / (float) s;

    x = x1;
    y = y1;

    putpixel(x1, y1, 4);

    for (m = 0; m < s; m++) {
    x += xi;
    y += yi;
    putpixel(x, y, 4);
    }
    getch();
}

/*=============================19Nov.,2010=============================*/