Line Drawing Algorithms

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

void startGraphics(){
    int gd=DETECT, gm;
    initgraph(&gd, &gm, "C:\\TURBOC3\\BGI");
}

void dda(int x1, int y1, int x2, int y2){
        int i, length, absx = abs(x2-x1), absy = abs(y2-y1);
        float dx, dy, x, y;
        absx>absy?(length=absx):(length=absy);
        dx = absx/length; dy = absy/length;
        dx>0?(x=x1+0.5):(x=x1-0.5); dy>0?(y=y1+0.5):(y=y1-0.5);
        putpixel((int)x, (int)y, 2);
        for(i=0; i<length; i++){
        x+=dx; y+=dy;
        putpixel((int)x, (int)y, 2);
        }
}

void bres(x1, y1, x2, y2){
    int i, x=x1, y=y1, dx = abs(x2-x1), dy = abs(y2-y1);
        float e = 2 * dy - dx;
        putpixel(x, y, 3);
        for(i=0; i<dx; i++){
        for(; e >=0; e-= 2*dx) y++;
        x++;
        e += 2*dy;
        putpixel(x, y, 3);
        }
}

void swap(int *a, int *b){
    int t = *a;
        *a = *b;
        *b = t;
}

void gbres(x1, y1, x2, y2){
        int i, x=x1, y=y1, dx = abs(x2-x1), dy = abs(y2-y1), flag = 0, sx, sy;
        float e;

        ((x2-x1)>0)?(sx=1):(sx=-1); ((y2-y1)>0)?(sy=1):(sy=-1);
        if(dx < dy){swap(&dx, &dy); flag = 1;}

        e = 2 * dy - dx;
        putpixel(x, y, 4);

        for(i=0; i<dx; i++){
            for(; e >=0; e -= 2*dx)
                    if(flag) x+=sx;
                    else y+=sy;
            if(flag) y+=sy;
            else x+=sx;
            e += 2*dy;
            putpixel(x, y, 4);
        }
}

void main(){
        char ch;
    startGraphics();
    cleardevice();

        ch = getch();
        if(ch=='d') dda(200, 200, 300, 300);
    else if(ch=='b') bres(200, 200, 300, 300);
    else if(ch=='g') gbres(200, 200, 300, 300);


    getch();
    closegraph();
}