(file-handler)+implemented write_to_file

First line is the data width, then the sand particles of each cell per
row.

file-handler.c

@@ -61,4 +61,19 @@ bool load_from_file(state_t *state, const char *filepath)
 }
 
 bool write_to_file(state_t *state, const char *filepath)
-{}
+{
+  FILE *fp = fopen(filepath, "w");
+  fprintf(fp, "%lu\n", state->dwidth);
+  for (size_t i = 0; i < state->dwidth; ++i)
+  {
+    for (size_t j = 0; j < state->dwidth; ++j)
+    {
+      fprintf(fp, "%d", state->data[(i * state->dwidth) + j]);
+      if (j != state->dwidth - 1)
+        fprintf(fp, ",");
+    }
+    fprintf(fp, "\n");
+  }
+  fclose(fp);
+  return true;
+}

main.c

@@ -117,6 +117,8 @@ int main(void)
 
   if (state.thread_alive)
     pthread_cancel(step_thread);
+
+  write_to_file(&state, "data.out");
   CloseWindow();
   return 0;
 }