Draw a polygon using mouse clicks

polygon.c

#include<stdio.h>
#include<graphics.h>
#include<dos.h>

void main() {
	int gd = DETECT, gm, gate, fx, fy, ax, ay, bx, by;
	union REGS i, o;
	initgraph(&gd, &gm, "C:\\TurboC3\\BGI");
	i.x.ax = 0;
	int86(0x33, &i, &o);
	i.x.ax = 1;
	int86(0x33, &i, &o);
	while (gate) {
		gate  = 1;
		i.x.ax = 5;
		i.x.bx = 0;
		int86(0x33, &i, &o);
		if (o.x.bx == 1) {
			gate = 0;
			fx = o.x.cx;
			fy = o.x.dx;
		}
	}
	ax = fx;
	ay = fy;
	do {
		gate = 1;
		while(gate) {
			i.x.ax = 5;
			i.x.bx = 0;
			int86(0x33, &i, &o);
			if (o.x.bx == 1) {
				gate = 0;
				bx = o.x.cx;
				by = o.x.dx;
			}
		}
		line(ax, ay, bx, by);
		ax = bx;
		ay = by;
	}while (!kbhit());
	line(fx, fy, ax, ay);
	delay(5000);
	getch();
}