Mandelbrot Set Generator in C by Robert J Morton

The first program below generates and displays the Mandelbrot Set. It also stores the image data in a file called mandel.dat. It could have been made to run faster. However, it's only for amusement!

//TO GENERATE THE MANDELBROT SET
#include < stdio.h>
#include < conio.h>
#include < graph.h>
#define XBIAS  395
#define YBIAS  240
main() {
  int c, e = 0, i;
  float cx, cy, x, y, z;
  FILE *h;
  _setvideomode(_VRES16COLOR);
  h = fopen("mandel.dat","w");
  for(cy = -2; cy < 2 && e == 0; cy += .01) {
    for(cx = -2.5; cx < 1.5 && e == 0; cx += .01) {
      for(x = .01, y = .01, c = 0, i = 0; i < 128; i++) {
        if(kbhit()) {e = 1; break;}
        z = x * y;
        x = x * x - y * y + cx;
        y = z + z + cy;
        if(x < -2.5 || x > 1.5 || y < -2 || y > 2) {
          if(i < 2) c = 1;           // dark blue
          else if(i < 3) c = 2;      // dark green
          else if(i < 4) c = 3;      // dark cyan
          else if(i < 5) c = 4;      // dark red
          else if(i < 6) c = 5;      // dark magenta
          else if(i < 7) c = 6;      // dark yellow
          else if(i < 8) c = 7;      // dark yellow
          else if(i < 9) c = 9;      // light blue
          else if(i < 10) c = 10;    // light green
          else if(i < 11) c = 11;    // light cyan
          else if(i < 12) c = 12;    // light red
          else if(i < 13) c = 13;    // light yellow
          else if(i < 14) c = 14;    // light yellow
          else c = 15;               // white
          _setcolor(c);
          _setpixel(
            XBIAS + (int)(cx * 100), YBIAS - (int)(cy * 100)
          );
          break;                     // break the i-loop
        }
      }
      if(h != NULL) putc(c, h);      // save pixel colour
    }
  }
  fclose(h);
  _settextposition(1, 1); printf("THE MANDELBROT SET");
  c = getchar();
  _setvideomode(_DEFAULTMODE);
}

To download a compiled version to run on a PC, right-click on mandel1.exe and save it to your local disk.

The second program here simply re-displays the Mandelbrot Set from the data previously stored in mandel.dat by the first program.

//TO RE-DISPLAY THE MANDELBROT SET [Compiled as Mandel2.exe]
#include < stdio.h>
#include < conio.h>
#include < graph.h>
#define XBIAS  370
#define YBIAS  240

main() {
  int c, e = 0, x, y;
  FILE *h;
  _setvideomode(_VRES16COLOR);
  _settextposition( 1,32); printf("THE MANDELBROT SET");
  _settextposition(30,31); printf("Hit C/R key to quit.");
  _setcolor(7);
  yscale( -260 ); yscale( 160 );
  xscale( -210 ); xscale( 210 );
  if(h = fopen("mandel.dat","r")) {
    for(y = -200; y < 201 && e == 0; y++)
      for(x = -250; x < 151; x++) {
        if(kbhit()) {e = 1; break;}
        _setcolor( getc(h) );
        _setpixel(XBIAS + x, YBIAS - y);
      }
    fclose(h);
  }
  else printf("Could not open data file.");
  c = getchar();
  _setvideomode(_DEFAULTMODE);
}

yscale(int a) {        //a = -260 or +160
  int y;
  _moveto (XBIAS + a, YBIAS - 200);
  _lineto (XBIAS + a, YBIAS + 200);
  for(y = -200; y < 201; y += 50) {
    _moveto (XBIAS + a - 5, YBIAS + y);
    _lineto (XBIAS + a + 5, YBIAS + y);
  }
}

xscale(int b) {        //b = -210 or +210
  int x;
  _moveto (XBIAS - 250, YBIAS + b);
  _lineto (XBIAS + 150, YBIAS + b);
  for(x = -250; x < 151; x += 50) {
    _moveto (XBIAS + x, YBIAS + b - 5);
    _lineto (XBIAS + x, YBIAS + b + 5);
  }
}

The compiled version of this program is mandel.exe, which you can download by right-clicking on its name and saving it to your local disk.

ODD FUNCTIONS

1. Square a Complex Number

(x + iy)²
= (x + iy)(x + iy)
= x² + i² y² + i2xy
= x² - y² + i2xy

SquareComplex(struct complex c) {
  double x = c -> r, y = c -> i, z;
  c -> r = x * x - y * y;        //Real part of square: x² - y² 
  z = r * i; c -> i = z + z;     //Imaginary part: 2xy
}

#define REALSCALE 128            //Screen pixel scaling factor
#define IMAGINERYSCALE 128       //Screen pixel scaling factor
     
DisplayComplex(struct complex c) {
  static int initialised = NO;
  if(initialised == NO) {
    _setvideomode(_VRES16COLOR); //Set to VGA 640 by 480 pixels 
    _setlogorg(320,240);         //Set origin to screen centre
    _setcolor(15);               //Set pixel colour bright white
    initialised = YES;           //Set the initialisation flag
  }
  _setpixel(                     //display the pixel
    (int)((c -> r) *= REALSCALE), 
    (int)((c -> i) *= IMAGINERYSCALE)
  );
}



/* I, Robert J Morton, author of these programs, am a poor 
   but right honourable fellow of the Ancient and Noble 
   Order of the Long-Term Unemployed.

   Please send any gratefully accepted offers of 
   programming work to robmorton@clara.net. */