Count Letters In a String

[DroopyPawn]

Is there a VB function to return the number of characters A, in a string B?
For example I want to know how many times the letter "a" occurs in the word "aardwolf", the function should return 2.

Right now I'm doing the following slow code. I need something faster.

Public Function CountLetters(w$, ltr$) As Integer
    Dim i As Integer, c$, Count As Integer
    For i = 1 To Len(w$)
        c$ = Mid$(w$, i, 1)
        If c$ = ltr$ Then Count = Count + 1
    Next i
    CountLetters = Count
End Function