John Conway's Game of Life using C++
Posted by Samath
Last Updated: January 04, 2017
  1595

A very simple C++ implementation of John Conway's Game of Life. This implementation uses several nested for loops as well as two-dimensional arrays to create a grid for the cells in the simulation to interact. The array that is displayed to the user is 50 x 100, but actual size of the array is 52 x 102.  The reason for this is to make the calculations easier for the cells on the outermost "frame" of the grid.

The Game of Life, also known simply as Life, is a cellular automaton devised by the British mathematician John Horton Conway in 1970. The "game" is a zero-player game, meaning that its evolution is determined by its initial state, requiring no further input. One interacts with the Game of Life by creating an initial configuration and observing how it evolves, or, for advanced "players", by creating patterns with particular properties.

Code:

#include <iostream>
#include <string>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

using namespace std;

//Copies one array to another.
void copy(int array1[52][102], int array2[52][102])
{
  for(int j = 0; j < 52; j++)
  {
		for(int i = 0; i < 102; i++) 			
			array2[j][i] = array1[j][i]; 
	}
}

//The life function is the most important function in the program.
//It counts the number of cells surrounding the center cell, and 
//determines whether it lives, dies, or stays the same.
void life(int array[52][102], char choice)
{
  //Copies the main array to a temp array so changes can be entered into a grid
  //without effecting the other cells and the calculations being performed on them.
  int temp[52][102];
  copy(array, temp);
	for(int j = 1; j < 51; j++)
 	{
 		for(int i = 1; i < 101; i++) 			
		{	
			if(choice == 'm')
			{
        //The Moore neighborhood checks all 8 cells surrounding the current cell in the array.
				int count = 0;
				count = array[j-1][i] + 
					array[j-1][i-1] +
					array[j][i-1] +
					array[j+1][i-1] +
					array[j+1][i] +
					array[j+1][i+1] +
					array[j][i+1] +
					array[j-1][i+1];
				//The cell dies.
        if(count < 2 || count > 3)
					temp[j][i] = 0;
				//The cell stays the same.
        if(count == 2)
					temp[j][i] = array[j][i];
				//The cell either stays alive, or is "born".
        if(count == 3)
					temp[j][i] = 1;
			}

			else if(choice == 'v')
			{
        //The Von Neumann neighborhood checks only the 4 surrounding cells in the array,
        //(N, S, E, and W).
				int count = 0;
				count = array[j-1][i] +
					array[j][i-1] +
					array[j+1][i] +
					array[j][i+1];	
        //The cell dies.  
				if(count < 2 || count > 3)
					temp[j][i] = 0;
				//The cell stays the same.
        if(count == 2)
					temp[j][i] = array[j][i];
				//The cell either stays alive, or is "born".
        if(count == 3)
					temp[j][i] = 1;
			}				
		}
 	}
  //Copies the completed temp array back to the main array.
  copy(temp, array);
}

//Checks to see if two arrays are exactly the same. 
//This is used to end the simulation early, if it 
//becomes stable before the 100th generation. This
//occurs fairly often in the Von Neumann neighborhood,
//but almost never in the Moore neighborhood.
bool compare(int array1[52][102], int array2[52][102])
{
	int count = 0;
	for(int j = 0; j < 52; j++)
	{
		for(int i = 0; i < 102; i++)
		{
			if(array1[j][i]==array2[j][i])
				count++;	
		}
	}
  //Since the count gets incremented every time the cells are exactly the same,
  //an easy way to check if the two arrays are equal is to compare the count to 
  //the dimensions of the array multiplied together.
	if(count == 52*102)
	  return true;
	else
	  return false;
}

//This function prints the 50 x 100 part of the array, since that's the only
//portion of the array that we're really interested in. A live cell is marked
//by a '*', and a dead or vacant cell by a ' '.
void print(int array[52][102])
{
	for(int j = 1; j < 51; j++)
 	{
 		for(int i = 1; i < 101; i++) 			
		{	
			if(array[j][i] == 1)
				cout << '*';
			else
				cout << ' ';
		}
		cout << endl;
 	}
}

int main()
{
	int gen0[52][102];
	int todo[52][102];
	int backup[52][102];
	char neighborhood;
	char again;
  char cont;
  bool comparison;
	string decoration;

  //Instructions on how the program is used, along with the rules of the game.
	cout << endl << "This program is a C++ implementation of John Conway's Game of Life."
	     << endl << "With it, you can simulate how \"cells\" interact with each other." << endl 
	     << endl << "There are two types of neighborhoods you can choose, the"
	     << endl << "Moore, and the Von Neumann.  The Moore neighborhood checks"
       << endl << "all 8 surrounding cells, whereas the Von Neumann checks"
       << endl << "only the 4 cardinal directions: (N, S, E, and W)." << endl
       << endl << "The rules of the \"Game of Life\" are as follows:" << endl
       << endl << "1. Any live cell with fewer than two live neighbors dies, as if caused by under-population."
       << endl << "2. Any live cell with two or three live neighbors lives on to the next generation."
       << endl << "3. Any live cell with more than three live neighbors dies, as if by overcrowding."
       << endl << "4. Any dead cell with exactly three live neighbors becomes a live cell, as if by reproduction." << endl
       << endl << "The initial configuration (Generation 0) of the board is determined randomly."
       << endl << "Every hundred Generations you will get the option to end or continue the simulation." 
       << endl << "If a system becomes \"stable\" (meaning the system does not change from one"
       << endl << "generation to the next), the simulation will end automatically." << endl << endl;
  //Loop to check if user wants to keep simulating.
  do
	{	
    //Loop to check for proper inputs.
    do
		{ 
      cout << "Which neighborhood would you like to use (m or v): ";
		  cin >> neighborhood;
		}while(neighborhood != 'm' && neighborhood != 'v');
    //Clears the screen so the program can start fresh.
    system("clear");
    int i = 0;
		//Loop that does the bulk of the simulation.
    do
		{
      //Generates the initial random state of the game board.
			srand(time(NULL));
      //The actual array is 102 x 52, but it's easier to just leave the surrounding part of
      //the array blank so it doesn't effect the calculations in the life function above.
			for(int j = 1; j < 51; j++)
			{
				for (int i = 1; i < 101; i++)
					gen0[j][i] = rand() % 2;
			}
      //Determines how big the decoration should be.
			if(i < 10)
				decoration = "#############";
			else if(i >= 10 && i < 100)
				decoration = "##############";
			else if(i >= 100 && i < 1000)
				decoration = "###############";
			else if(i >= 1000 && i < 10000)
				decoration = "################";
			else
				decoration = "#################";
      //Prints the generation.  If i == 0, the gen0 array is copied to the 
      //todo array, and is printed before any functions act upon it.
			cout << decoration << endl << "Generation " << i 
			     << ":" << endl << decoration << endl << endl;
      //Initializes the arrays by copying the gen0 array to the todo array.
      if(i == 0)
				copy(gen0, todo);  
			copy(todo, backup);			
			print(todo);		
		  life(todo, neighborhood);
		  i++;
      //Pauses the system for 1/10 of a second in order to give the screen
      //time to refresh.
      system("sleep .1");
      //Checks whether the generation is a multiple of 100 to ask 
      //the user if they want to continue the simulation. If they
      //wish to end, the program breaks out of the loop to ask if
      //the user wishes to run another simulation.
      if(i % 100 == 1 && i != 1)
      {
        cout << endl;
        //Loop to check for proper inputs.
        do
        {
          cout << "Would you like to continue this simulation? (y/n): ";
          cin >> cont;
        }while(cont != 'y' && cont != 'n');
        if(cont == 'n')
          break;
      }
      //Compares the current generation with a backup generation.
      //If they aren't the same (they usually aren't) the system
      //clears the screen and repeats the process until they are
      //the same or the user chooses to quit.
      comparison = compare(todo, backup);
      if(comparison == false)
        system("clear");
      if(comparison == true)
        cout << endl;
		}while(comparison == false); 
    //Loop to check for proper inputs.
    do
    {
      cout << "Would you like to run another simulation? (y/n): ";
		  cin >> again;
    }while(again != 'y' && again != 'n');
	}while(again == 'y');
	return 0;
}