Simple Game of Life

life.c

#include <stdio.h>
#include <unistd.h>

#define COLS 25
#define ROWS 25
#define ALIVE 1
#define DEAD 0

void printgrid(char *grid) {
  printf("\033[H\033[2J");
  for (int r = 0; r < ROWS; r++) {
    for (int c = 0; c < COLS; c++) {
      if (grid[r * COLS + c] == DEAD) {
        printf("  ");
      } else {
        // printf("**");
        printf("██");
      }
    }
    printf("\n");
  }
}

int countneighbours(char *grid, int r, int c) {
  int count = 0;
  for (int i = r - 1; i < r + 2; i++) {
    for (int j = c - 1; j < c + 2; j++) {
      if (i >= 0 && i < ROWS && j >= 0 && j < COLS) {
        if (grid[i * COLS + j] && !(i == r && j == c))
          count++;
      }
    }
  }
  return count;
}

int main(void) {
  // 1 is alive, 0 is dead
  char grid[COLS * ROWS] = {
      0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
      0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
      0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
      1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
  };
  while (1) {

    // Render grid
    printgrid(grid);

    // Init new grid
    char new_grid[COLS * ROWS];
    for (int i = 0; i < COLS * ROWS; i++) {
      new_grid[i] = DEAD;
    }

    // Create new grid
    for (int r = 0; r < ROWS; r++) {
      for (int c = 0; c < COLS; c++) {
        int neighbours = countneighbours(grid, r, c);
        char alive = grid[r * COLS + c] == ALIVE;
        // 1. Any live cell with fewer than two live neighbours dies, as if by
        // underpopulation.
        if (alive && neighbours < 2) {
          new_grid[r * COLS + c] = DEAD;
        }
        // 2. Any live cell with two or three live neighbours lives on to the
        // next generation.
        else if (alive && (neighbours == 2 | neighbours == 3)) {
          new_grid[r * COLS + c] = ALIVE;
        }
        // 3. Any live cell with more than three live neighbours dies, as if
        // by overpopulation.
        else if (alive && neighbours > 3) {
          new_grid[r * COLS + c] = DEAD;
        }
        // 4. Any dead cell with exactly three live neighbours becomes a live
        // cell, as if by reproduction.
        else if (!alive && neighbours == 3) {
          new_grid[r * COLS + c] = ALIVE;
        }
      }
    }

    // Update the old grid
    for (int i = 0; i < COLS * ROWS; i++) {
      grid[i] = new_grid[i];
    }

    usleep(50000); // 50ms delay
  }
}