/* scanning all blocks */
    fprintf(stdout, "\n");
    int block_size = (int)(sqrt(grid_size));
    for(int b = 0; b < (int)grid_size; b++) {
      fprintf(stdout, "\nblock %d: ", b);

      for(int k = 0; k < (int)grid_size; k++) {
    int i_grid = (k/block_size) + (b/block_size)*block_size;
    int j_grid = (k % block_size) + (b % block_size)*block_size;

    subgrid[k] = &grid[i_grid][j_grid];

    char string[MAX_COLORS+1];
    pset2str(string, *(subgrid[k]));
    fprintf(stdout, "(%d,%d) = '%s', ", i_grid, j_grid, string);
      }
    }