VB.net Expression does not produce a value error

Question

I am brand new to vb.net and programming in general so sorry if this is a basic error but im trying to make ax's and o's game in vb.net and it keeps saying that my CheckForWin does not produce a value which makes zero sense to me and when i looked it up the only questions were about converting different code to vb.net and said nothing about the problem i was having This my code: Public Class Form1

Dim Board(9) As String
Dim Player1 As String = "X"
Dim Player2 As String = "O"

Public Property X As String

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load

End Sub

Private Sub ResetBoard()
    Do
        If CheckForWin() = True Then
            Board(0) = 0
            Board(1) = 0
            Board(2) = 0
            Board(3) = 0
            Board(4) = 0
            Board(5) = 0
            Board(6) = 0
            Board(7) = 0
            Board(8) = 0

        End If
    Loop Until Board(0) = 0
    Board(1) = 0
    Board(2) = 0
    Board(3) = 0
    Board(4) = 0
    Board(5) = 0
    Board(6) = 0
    Board(7) = 0
    Board(8) = 0
End Sub

Private Sub CheckForWin()
    If "0""3""6" = X Then
        ResetBoard()
    ElseIf "1""4""7" = X Then
        ResetBoard()
    ElseIf "2""5""8" = X Then
        ResetBoard()
    ElseIf "0""1""2" = X Then
        ResetBoard()
    ElseIf "3""4""5" = X Then
        ResetBoard()
    ElseIf "6""7""8" = X Then
        ResetBoard()
    ElseIf "0""4""8" = X Then
        ResetBoard()
    ElseIf "2""4""6" = X Then
        ResetBoard()
    ElseIf "0""3""6" = 0 Then
        ResetBoard()
    ElseIf "1""4""7" = 0 Then
        ResetBoard()
    ElseIf "2""5""8" = 0 Then
        ResetBoard()
    ElseIf "0""1""2" = 0 Then
        ResetBoard()
    ElseIf "3""4""5" = 0 Then
        ResetBoard()
    ElseIf "6""7""8" = 0 Then
        ResetBoard()
    ElseIf "0""4""8" = 0 Then
        ResetBoard()
    ElseIf "2""4""6" = 0 Then
        ResetBoard()
    End If
End Sub

End Class

The problem lies within this line of code: If CheckForWin() = True Then

Answer 1

This line of code:

If CheckForWin() = True Then
    ...
End If

This sets up a conditional check to see if the result of the CheckForWin method is true. The issue is that the method is a Sub routine and not a Function.

A Function represents a block of code that returns a value whereas a Sub also represents a block of code but it does not return a value.

What's more is that it appears as if you have fallen into an infinite loop. ResetBoard calls CheckForWin which calls ResetBoard which calls... and so on.

The simplest thing to do would be to:

1. Convert the CheckForWin to a Function
2. Stop calling ResetBoard in the CheckForWin method
3. Return True when any of your conditional checks in the ResetBoard method is True

Here is an example:

Private Sub ResetBoard()
    ' check if there is a winner, if not then stop execution of the method early
    Dim isWin = CheckForWin()
    If (Not isWin) Then
        Return
    End If

    For index = 1 To 8
        Board(index) = 0
    Next
End Sub

Private Function CheckForWin() As Boolean
    Dim winningPatterns = {
        "0""3""6",
        "1""4""7",
        "2""5""8",
        ' etc...
    }
    Dim doAnyMatch = winningPatterns.Contains(X)
    Return doAnyMatch
End Function