Fundamentals of Programming: Two-Dimensional Arrays
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.

Depending on the language you are writing in, the format of an array address can change. In VB.NET it is, as shown in the diagram above, with y,x |
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:
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
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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 whiteAnswer: 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 parameterAnswer: 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 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):
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) = ""
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Noughts and Crosses
editAnother 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: 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
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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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