I'm trying to make hangman game from VB, it went fine but I need help with keeping track of the letters that the user has inputted in the inputbox. If the user has entered the same letter twice then a messagebox appears saying that the user has already guessed that letter. Heres the code:

Code:
Option Explicit

Private Sub cmdPlayGame_Click()
    Const strSentinel As String = "!"

    Dim strSecretWord As String, intSecretWordLength As Integer
    Dim intNumberOfGuesses As Integer
    Dim strGuess As String, strWordGuessedSoFar As String
    Dim intLetterPos As Integer

    strSecretWord = "magic"
    intSecretWordLength = Len(strSecretWord)
    strWordGuessedSoFar = String(intSecretWordLength, "-")
    lblWord.Caption = strWordGuessedSoFar

    intNumberOfGuesses = 0

    strGuess = InputBox("Guess a letter (! to guess word)", "Hangman")
    Do While strGuess <> strSentinel
        intNumberOfGuesses = intNumberOfGuesses + 1
        For intLetterPos = 1 To intSecretWordLength
            If StrComp(strGuess, Mid(strSecretWord, intLetterPos, 1), vbTextCompare) = 0 Then
                Mid(strWordGuessedSoFar, intLetterPos, 1) = strGuess
            End If
        Next intLetterPos
        lblWord.Caption = strWordGuessedSoFar
        strGuess = InputBox("Guess a letter (! to guess word)", "Hangman")
    Loop

    If strGuess = strSentinel Then
        strGuess = InputBox("Guess the word")
    End If

    If StrComp(strGuess, strSecretWord, vbTextCompare) = 0 Then
        MsgBox "You win! It took you " & intNumberOfGuesses & " guesses."
    Else
        MsgBox "You lose. Press OK to display secret word."
    End If

    lblWord.Caption = strSecretWord
End Sub

Private Sub cmdDone_Click()
    Unload Me
End Sub