 # C++: Conway’s Game of Life The Game of Life is a cellular automaton devised by the British mathematician John Horton Conway in 1970. It is the best-known example of a cellular automaton.

Conway’s game of life is described here:

A cell C is represented by a 1 when alive or 0 when dead, in an m-by-m square array of cells. We calculate N – the sum of live cells in C’s eight-location neighbourhood, then cell C is alive or dead in the next generation based on the following table:

```   C   N                 new C
1   0,1             ->  0  # Lonely
1   4,5,6,7,8       ->  0  # Overcrowded
1   2,3             ->  1  # Lives
0   3               ->  1  # It takes three to give birth!
0   0,1,2,4,5,6,7,8 ->  0  # Barren
```

Assume cells beyond the boundary are always dead.

The “game” is actually a zero-player game, meaning that its evolution is determined by its initial state, needing no input from human players. One interacts with the Game of Life by creating an initial configuration and observing how it evolves.

Although you should test your implementation on more complex examples such as the glider in a larger universe, show the action of the blinker (three adjoining cells in a row all alive), over three generations, in a 3 by 3 grid.

Considering that the simplest implementation in C++ would lack any use of the object-oriented paradigm, this code was specifically written to demonstrate the various object-oriented features of C++. Thus, while it is somewhat verbose, it fully simulates Conway’s Game of Life and is relatively simple to expand to feature different starting shapes.

```#include <iostream>
#define HEIGHT 4
#define WIDTH 4

struct Shape {
public:
char xCoord;
char yCoord;
char height;
char width;
char **figure;
};

struct Glider : public Shape {
static const char GLIDER_SIZE = 3;
Glider( char x , char y );
~Glider();
};

struct Blinker : public Shape {
static const char BLINKER_HEIGHT = 3;
static const char BLINKER_WIDTH = 1;
Blinker( char x , char y );
};

class GameOfLife {
public:
GameOfLife( Shape sh );
void print();
void update();
char getState( char state , char xCoord , char yCoord , bool toggle);
void iterate(unsigned int iterations);
private:
char world[HEIGHT][WIDTH];
char otherWorld[HEIGHT][WIDTH];
bool toggle;
Shape shape;
};

GameOfLife::GameOfLife( Shape sh ) :
shape(sh) ,
toggle(true)
{
for ( char i = 0; i < HEIGHT; i++ ) {
for ( char j = 0; j < WIDTH; j++ ) {
world[i][j] = '.';
}
}
for ( char i = shape.yCoord; i - shape.yCoord < shape.height; i++ ) {
for ( char j = shape.xCoord; j - shape.xCoord < shape.width; j++ ) {
if ( i < HEIGHT && j < WIDTH ) {
world[i][j] =
shape.figure[ i - shape.yCoord ][j - shape.xCoord ];
}
}
}
}

void GameOfLife::print() {
if ( toggle ) {
for ( char i = 0; i < HEIGHT; i++ ) {
for ( char j = 0; j < WIDTH; j++ ) {
std::cout << world[i][j];
}
std::cout << std::endl;
}
} else {
for ( char i = 0; i < HEIGHT; i++ ) {
for ( char j = 0; j < WIDTH; j++ ) {
std::cout << otherWorld[i][j];
}
std::cout << std::endl;
}
}
for ( char i = 0; i < WIDTH; i++ ) {
std::cout << '=';
}
std::cout << std::endl;
}

void GameOfLife::update() {
if (toggle) {
for ( char i = 0; i < HEIGHT; i++ ) {
for ( char j = 0; j < WIDTH; j++ ) {
otherWorld[i][j] =
GameOfLife::getState(world[i][j] , i , j , toggle);
}
}
toggle = !toggle;
} else {
for ( char i = 0; i < HEIGHT; i++ ) {
for ( char j = 0; j < WIDTH; j++ ) {
world[i][j] =
GameOfLife::getState(otherWorld[i][j] , i , j , toggle);
}
}
toggle = !toggle;
}
}

char GameOfLife::getState( char state, char yCoord, char xCoord, bool toggle ) {
char neighbors = 0;
if ( toggle ) {
for ( char i = yCoord - 1; i <= yCoord + 1; i++ ) {
for ( char j = xCoord - 1; j <= xCoord + 1; j++ ) {
if ( i == yCoord && j == xCoord ) {
continue;
}
if ( i > -1 && i < HEIGHT && j > -1 && j < WIDTH ) {
if ( world[i][j] == 'X' ) {
neighbors++;
}
}
}
}
} else {
for ( char i = yCoord - 1; i <= yCoord + 1; i++ ) {
for ( char j = xCoord - 1; j <= xCoord + 1; j++ ) {
if ( i == yCoord && j == xCoord ) {
continue;
}
if ( i > -1 && i < HEIGHT && j > -1 && j < WIDTH ) {
if ( otherWorld[i][j] == 'X' ) {
neighbors++;
}
}
}
}
}
if (state == 'X') {
return ( neighbors > 1 && neighbors < 4 ) ? 'X' : '.';
}
else {
return ( neighbors == 3 ) ? 'X' : '.';
}
}

void GameOfLife::iterate( unsigned int iterations ) {
for ( int i = 0; i < iterations; i++ ) {
print();
update();
}
}

Glider::Glider( char x , char y ) {
xCoord = x;
yCoord = y;
height = GLIDER_SIZE;
width = GLIDER_SIZE;
figure = new char*[GLIDER_SIZE];
for ( char i = 0; i < GLIDER_SIZE; i++ ) {
figure[i] = new char[GLIDER_SIZE];
}
for ( char i = 0; i < GLIDER_SIZE; i++ ) {
for ( char j = 0; j < GLIDER_SIZE; j++ ) {
figure[i][j] = '.';
}
}
figure = 'X';
figure = 'X';
figure = 'X';
figure = 'X';
figure = 'X';
}

Glider::~Glider() {
for ( char i = 0; i < GLIDER_SIZE; i++ ) {
delete[] figure[i];
}
delete[] figure;
}

xCoord = x;
yCoord = y;
for ( char i = 0; i < BLINKER_HEIGHT; i++ ) {
}
for ( char i = 0; i < BLINKER_HEIGHT; i++ ) {
for ( char j = 0; j < BLINKER_WIDTH; j++ ) {
figure[i][j] = 'X';
}
}
}

for ( char i = 0; i < BLINKER_HEIGHT; i++ ) {
delete[] figure[i];
}
delete[] figure;
}

int main() {
Glider glider(0,0);
GameOfLife gol(glider);
gol.iterate(5);
gol2.iterate(4);
}
```
Output:

first a glider, then a blinker, over a few iterations

(reformatted for convenience).

```.X.. .... .... .... ....
..X. X.X. ..X. .X.. ..X.
XXX. .XX. X.X. ..XX ...X
.... .X.. .XX. .XX. .XXX
==== ==== ==== ==== ====

.X.. .... .X..
.X.. XXX. .X..
.X.. .... .X..
.... .... ....
==== ==== ====```

SOURCE

Content is available under GNU Free Documentation License 1.2.