c - Mandelbrot PPM drawing is always black -

i want draw mandelbrot ppm file in c. code working drawing black. have code wikia. key success think "alfa" (i think so). have no idea alfa should be. here's code:

#include <stdio.h> #include <stdlib.h>  #define w 800 #define h 800  //rgb struct struct rgb {     int r;     int g;     int b; }; struct rgb picture[w][h];  void draw() { int i, j, iteration, max_iteration, alfa, color; float x, y, x0, y0, xtemp;  for(i=0;i<w;++i) {     for(j=0;j<h;++j)     {          x0 = 1; //scaled x (e.g interval(-2.5, 1))          y0 = -1; //scaled y (e.g interval(-1, 1))          x = 0.0;          y = 0.0;          iteration = 0;          max_iteration = 1000;           while (x*x + y*y < 2*2 && iteration < max_iteration)          {              xtemp = x*x - y*y + x0;              y = 2*x*y + y0;              x = xtemp;              iteration = iteration+ 1;              alfa = x*y; //???          }           color = alfa * (iteration / max_iteration);           picture[i][j].r = color;          picture[i][j].g = color;          picture[i][j].b = color;     } } }  int main() {  //variables int i,j;  draw();  file *fp; fp = fopen("picture.ppm", "w"); fprintf(fp,"p3\n#test\n%d %d\n256\n", w, h);  (i=0; < w; ++i)     {         (j=0; j < h; ++j)         {         fprintf(fp,"%d %d %d ", picture[i][j].r, picture[i][j].g , picture[i][j].b);         }     fprintf(fp, "\n");     }  fclose(fp);  return 0; } 

in line

color = alfa * (iteration / max_iteration); 

the divison iteration / max_iteration int division result 0 (possibly 1 if ever iteration == max_iteration).

try working in float, or rearrange this

color = alfa * iteration / max_iteration; 

removing parentheses. you'll have watch out int range isn't broken.

having said that, seems not sure alfa is. suggest 255 grey-scale image.