Why do my gliders never delete and instead remain in the bottom of my screen in my Game of Life sim?

user_16368306 0
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I am attempting to code a console based Conway's game of life simulator but for some reason when my gliders reach the bottom of the screen they turn into a stationary 2*2 square that never dissapears, I have no idea why they are there or what is causing it. To see them you might need to wait five or six generations.

code:

#include<stdio.h>
#include<stdlib.h>
#include<conio.h>
#ifdef __unix__
# include <unistd.h>
#elif defined _WIN32
# include <windows.h>
#define sleep(x) Sleep(1000 * (x))
#endif

int sizeX = 20;
int sizeY = 20;

int grid[20][20] = {{0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0},
                    {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},
                    {0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0},
                    {0,0,0,1,0,0,0,0,0,1,0,1,0,0,0,0,0,0,0,0},
                    {0,0,0,0,0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,0},
                    {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},
                    {0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0},
                    {0,0,0,0,0,1,0,1,0,0,0,0,0,0,0,0,0,0,0,0},
                    {0,0,0,0,0,0,1,1,0,0,0,0,0,0,0,0,0,0,0,0},
                    {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0}};

int count_nbr(int grid[sizeX][sizeY], int x, int y){
 int n_count = 0;
 if (grid[x-1][y-1]==1)
     n_count++;

 if(grid[x-1][y]==1)
     n_count++;

 if(grid[x-1][y+1]==1)
     n_count++;

 if(grid[x][y-1]==1)
     n_count++;

 if(grid[x][y+1]==1)
     n_count++;

 if(grid[x+1][y-1]==1)
     n_count++;

 if(grid[x+1][y]==1)
     n_count++;

 if(grid[x+1][y+1]==1)
     n_count++;

 return n_count;
}

int main(void){
 int neighbour_count[sizeX][sizeY];
    int x,y,iterations;

 for(iterations=0;iterations<500;iterations++){
  system("cls"); //Clear screen
  for(x=0;x<sizeX;x++){
    printf("\n");
    for(y=0;y<sizeY;y++){
     if(grid[x][y]==1){
      printf("@");
             }
    else{
      printf(" ");
    }
    neighbour_count[x][y] = count_nbr(grid,x,y);
         }
  }
                    
  for(x=0;x<sizeX;x++){
     for(y=0;y<sizeY;y++){
        if(neighbour_count[x][y] < 2 || neighbour_count[x][y] > 3)
     grid[x][y] = 0;
    else if(neighbour_count[x][y] == 3)
     grid[x][y]=1;
   }
  }
  printf("\n");
 }
}
cellular-automata conways-game-of-life console-application c
1 Answers

There may be bugs in your code, but the behavior you observe is not one. Instead, it's exactly what you'd expect to see in Conway's Game of Life played on a finite grid, with boundary conditions specifying that all cells outside the grid edges are to be always treated as dead:

1:        2:        3:        4:        5:        6:
......    ......    ......    ......    ......    ......
...X..    ..X...    ...X..    ......    ......    ......
.X.X.. -> ...XX. -> ....X. -> ..X.X. -> ....X. -> ...XX.
..XX..    ..XX..    ..XXX.    ...XX.    ...XX.    ...XX.
######    ######    ######    ######    ######    ######

Here, X denotes a live cell, . denotes a dead cell that could become live, and # denotes a cell outside the grid boundary that is always treated as dead.

In step 3 above, one of the always-dead cells marked with # has three live neighbors. If it was a normal dead cell, it would become live in step 4 and the glider would continue to propagate. But because it can't become live, what actually appears in step 4 is a four-cell pattern consisting of a glider with one live cell missing. This pattern then evolves in two steps into a 2x2 block (and stays that way, as the block is a stable still life).

user_4110220
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