# title=Fundamentals of Programming: Two-Dimensional Arrays

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You have already learnt how to use one dimensional arrays in your computer programs. You should be familiar with code such as:

```Dim friends(6) As String

friends(0) = "Barry"
friends(1) = "Monica"
friends(2) = "Xiao"
```

This is great for storing lists of things, but what about if we want to simulate something more complex such as a game board or a map? Wouldn't it be great if we could use a two-dimensional array?

Most major programming languages allow you to use two-dimensional arrays. They work in much the same way as a one-dimensional array but allow you to specify a column index and a row index.

We can create the two-dimensional array shown above and assign values by doing the following:

```Dim grid(4,4) As String

grid(0,3) = "A"
grid(3,2) = "B"
grid(1,4) = "C"
Console.Writeline("The content of 3,2 is:" & grid(3,2))
```
Example: Two-Dimensional Arrays

Two-dimensional arrays are very useful and a good place to get started is to create your own version of the game Battleships with a 4 cell by 4 cell grid. See if you can win, or even break it!

We are modelling the following board using the two dimensional board variable:

0 1 2 3
0 x o o o
1 o o x o
2 o o o o
3 o o o o
```Dim x, y As Integer
Dim board(3, 3) As Char

board(0, 0) = "x"
board(0, 1) = "o"
board(0, 2) = "o"
board(1, 0) = "o"
board(1, 1) = "o"
board(1, 2) = "x"
board(2, 0) = "o"
board(2, 1) = "o"
board(2, 2) = "o"
board(2, 0) = "o"
board(2, 1) = "o"
board(2, 2) = "o"

For z = 1 To 3
Console.WriteLine("This is guess number " & z)

Console.Write("please insert you x location:")
x = Console.ReadLine()
Console.Write("please insert you y location:")
y = Console.ReadLine()
If board(x, y) = "x" Then
Console.WriteLine("you win!")
End If
Next
```
 Exercise: Two-Dimensional Arrays Declare an array to make a small checkers board of type char, 3 squares by 3 squares Answer: ```dim checkBoard(3,3) as char 'also checkBoard(2,2) ``` create a chequered pattern using `b` for black and `w` for white Answer: ``` checkBoard(1, 1) = "b" checkBoard(1, 2) = "w" checkBoard(1, 3) = "b" checkBoard(2, 1) = "w" checkBoard(2, 2) = "b" checkBoard(2, 3) = "w" checkBoard(3, 1) = "b" checkBoard(3, 2) = "w" checkBoard(3, 3) = "b" ``` A much smarter way is to use a loop, this will allow for you to quickly create an board of any size you wish. There is a question coming up that will want you to build this! Write a sub routine to `display` this board (HINT: you need loops), that takes checkBoard as a parameter Answer: ```sub display(checkBoard()) for x = 1 to 3 for y = 1 to 3 console.write(checkBoard(x,y)) Next console.writeline() Next ``` Declare a chessBoard (8*8 squares), programmatically colour it in with `b` for black and `w`. You might want to look for a pattern in the colour assignments for the checker board above and make friends with the MOD function You might also go a little loopy trying to answer this question Answer: ```dim chessBoard(8,8) as char 'also chessBoard(7,7) for x = 1 to 8 for y = 1 to 8 if (x + y) MOD 2 = 1 then chessBoard(x,y) = "w" else chessBoard(x,y) = "b" end if next next display(chessBoard()) ' using a slightly updated version of the subroutine display() ``` If you've done this you might want to get the program to print some massive boards, whatever floats your boat. Using the following two-dimensional array, grid(4,4): Write code to output the name `CRAIG` Insert `MARY` on row 2 (the third row) Overwite `STEVE` with `SAM` Answer: ```Console.Writeline(grid(3,0) & grid(3,1) & grid(3,2) & grid(3,3) & grid(3,4)) grid(2,0) = "M" grid(2,1) = "A" grid(2,2) = "R" grid(2,3) = "Y" grid(1,0) = "S" grid(1,1) = "A" ' you could skip this grid(1,2) = "M" grid(1,3) = "" grid(1,4) = "" ```

## Noughts and Crosses

Another game you might play on a 2D grid is the popular game of noughts and crosses:

To do this we need to build a 3 by 3 grid:

```Sub main()
Dim board(3, 3) As Char

board(1, 1) = "-"
board(1, 2) = "-"
board(1, 3) = "-"
board(2, 1) = "-"
board(2, 2) = "-"
board(2, 3) = "-"
board(3, 1) = "-"
board(3, 2) = "-"
board(3, 3) = "-"

'main game function call to go here
end sub
```

Next we need a subroutine to display the grid, passing the board as a parameter

```Sub display(ByVal b(,) As Char)
For i = 0 To 3
For j = 0 To 3
Console.Write(b(i, j))
Next

Console.WriteLine()
Next
End Sub
```

We need the ability to check whether the game has been won and who has won it. We'll do this by building a win check that returns `true` if the specified player has won, or `false` otherwise. We need to pass it some values to check, namely the board - `b()` and the player you are checking for - `p`. Both are passed `byVal` as we don't need to change them:

```Function win(ByVal b(,) As Char, ByVal p As Char)
If b(1, 1) = p And b(1, 2) = p And b(1, 3) = p Then 'first row check
Console.WriteLine(p + " WINS!")
Return True
ElseIf b(2, 0) = p And b(2, 1) = p And b(2, 2) = p Then 'second row check
Console.WriteLine(p + " WINS!")
Return True
Else
Return False 'if the game hasn't been won
End If
' this needs more rules, it only has 2 at the moment and one of them doesn't work!  Could you use a loop instead?
End Function
```

It's a bit of a rubbish game so far, so we better let someone move:need the ability for players to play a move:

```Sub move(ByRef b(,) As Char, ByVal p As Char)
Dim x, y As Integer
Dim move As String
Console.WriteLine(p + " - make your move in the format: x,y")
move = Console.ReadLine()
x = move.Substring(0, 1)
y = move.Substring(2, 1)
If b(x, y) = "-" Then
b(x, y) = p
display(b)
Else
Console.WriteLine("Invalid move!  Miss a turn")
End If
End Sub
```

We need to end the game in a draw if all the spaces have been taken

```Function drawn(ByVal b(,) As Char)
Dim c As Integer = 0 ' set a counter to keep track of how many spaces there are
For i = 0 To 3
For j = 0 To 3
If b(i, j) = "-" Then
c = c + 1
End If
Next
Next

If c = 9 Then
Console.WriteLine("Draw, game over!")
Return True
Else
Return False
End If
End Function
```

Finally we'll bring everything together

```Sub Main()
'array declaration from earlier...

game(board)
console.readline()
End Sub

Sub game(ByVal b(,) As Char)
Dim togo As Char
Do
If togo = "x" Then
togo = "o"
Else
togo = "x"
End If

move(b, togo)
display(b)
Loop While Not (win(b, togo)) And Not (drawn(b))
End Sub
```
 Exercise: More Two-Dimensional arrays Fix the program above so that an incorrect move allows the user to try again: xxo o-- --- x - make your move in the format: x,y 1,2 x - make your move in the format: x,y 1,2 x - make your move in the format: x,y Answer: ```sub move(byRef b() As Char, byVal p As Char) dim x,y as integer dim move as string Do console.writeline(p + " - make your move in the format: x,y") move = console.readline() x = move.Substring(0, 1) y = move.Substring(2, 1) While b(x + 1,y + 1) <> "-" b(x + 1,y + 1) = p display(byVal b()) end sub ``` Fix the program above so that is checks rows, columns and diagonals for a winning position. Try to keep your answer below 19 lines and 550 characters. Answer: ```function win(ByVal b(,) As Char, byVal p As Char) for x = 0 to 2 if b(x,0) = p AND b(x,1) = p AND b(x,2) = p then 'check columns console.writeline(p + " WINS!") return true next for y = 0 to 2 if b(0,y) = p AND b(1,y) = p AND b(2,y) = p then 'check rows console.writeline(p + " WINS!") return true next if b(0,0) = p AND b(1,1) = p AND b(2,2) = p then 'second row check console.writeline(p + " WINS!") return true end if if b(0,2) = p AND b(1,1) = p AND b(2,0) = p then 'second row check console.writeline(p + " WINS!") return true end if return false 'if the game hasn't been won end function ```
 Extension: Many more dimensional arrays You have met one and two dimensional arrays so far, but this isn't the limit to the number of dimensions that you can use. For example you might want to model a three dimensional world by using a 3D array ```Dim space(2, 2, 2) As integer ' 3 dimensional array ```

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