Listing 1

/* The following declarations are excerpted from my Mandelbrot
program's header file; since practically the whole program
consists of specialized functions useful in this task only, all
variables related to the screen and to the map are global and
there is relatively little ``information hiding'' and parameter
passing. */

struct pt target, center;
struct {double x, y;} orig;	/* this is a pixel, but it is
				stored as a double because it can easily get
				bigger than a long integer */	
double a_step, b_step, a, b, xbeg, ybeg;
int make_frame, imported;
unsigned int scrwid, scrht, times, step, disc, pelrow, pelcol;
unsigned int maxx, maxy, scrx0, scry0, discrim;
unsigned long mag, ncalcs;
#define VIEWAR 1.33  /* screen aspect ratio */

int iter(a,b,t,d)

double a, b;
int t, d;

{
register int n = 0, tt;
double x, y, xx, yy, xxx;
extern int chkkbd();

	x = y = 0;
	tt = t;
	while (n < tt && (xx = x*x) + (yy = y*y) < d)
	{	xxx = xx - yy + a;
		y = 2*x*y + b;
		x = xxx;
		n++;
	}
     if (chkkbd() == 27)
		return -1;
	if (n == t) return 0;
	else return n;
}	

#include <conio.h>

int chkkbd()

{
extern int kbhit(), getch();

	return kbhit() ? getch() : 0;
}



Listing 2

void makemap()

{
register int n;

	for (;pelrow<scrht;pelrow++)
	{    a = xbeg;
		for (pelcol=0;pelcol<scrwid;)
		{    n = iter(a,b,times,discrim);
			ncalcs += n == 0 ? times : n;
			if (n)
			   pset(scrx0+pelcol,scry0+pelrow,(n/step)%15+1);
		     a += a_step;
			pelcol++;
		}
	     b += b_step;
	}
}


Listing 3

int setparms() 
 
{ 
double half_width, half_height, xend, yend; 
 
	if (scrwid != maxx)		 
	{	scrht = (int)(maxy * (double)scrwid/maxx); 
		make_frame = 1; 	/* draw a line around it */
	} 
	else scrht = maxy; 	/* maxx by maxy would be full screen */
	scrx0 = (maxx - scrwid)/2; /* upper left corner of map in
							pixel positions */
	scry0 = (maxy - scrht)/2; 
	center.x = target.x; 
	center.y = target.y; 
	discrim = disc * disc; 
	half_width = (double)3.0/(2*mag);	/* total length of M is
								3; mag == 1 shows whole
								set */ 
	xend = center.x + half_width; 	/* I don't think this
							sequence of events is actually
							as silly as it looks */
	half_height = half_width / VIEWAR; 
	yend = center.y - half_height; 
	xbeg = center.x - half_width; 
	ybeg = center.y + half_height; 
	a_step = (xend - xbeg) / scrwid; /* Mandelunits per pixel */
	b_step = (yend - ybeg) / scrht;   /* ditto, y axis */
	orig.x = scrx0 + scrwid/2 + (-center.x/a_step);	/* pixel
					location of M's origin <197> used in the
					aim-and-frame routine */
	orig.y = scry0 + scrht/2 - (center.y/b_step);   
     if (!imported) 
	{	b = ybeg; 
		pelrow = 0; 
		ncalcs = 0; 
	} 
	else b = ybeg + b_step * pelrow; /* resume incomplete map */
	imported = 0; 
	return make_frame; 
}