A-level Computing/AQA/Problem Solving, Programming, Data Representation and Practical Exercise/Fundamentals of Programming/Two-Dimensional Arrays

One-Dimensional Arrays Fields, Records and Files 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. thumb|center|Treat a 2D array like a grid, the location of a cell is shown above 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)) thumb|center|The code would also output the value B 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 dim checkBoard(3,3) as char 'also checkBoard(2,2) create a chequered pattern using b for black and w for white 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 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 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 200px 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: center|Game of tic-tac-toe, won by X 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 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. 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 One-Dimensional Arrays Fields, Records and Files