Option Compare Database
Option Explicit

Function LargestDigit%(n)

Dim str As String
Dim l As Long
Dim max As Variant
Dim curr As Variant

str = CStr(n)

For l = 1 To Len(str)
    curr = Mid(str, l, 1)
    If max < curr Then
        max = curr
    End If
Next

LargestDigit = max

End Function

Function LDigit%(n)
    Dim s$, i%
    
    s = CStr(n)
    For i = 9 To 1 Step -1
        If InStr(1, s, CStr(i)) > 0 Then _
        Exit For
    Next i
    LDigit = i
End Function

Sub testspeed()
    Dim n, t#, i&
    n = 12345678912345#
    t = Timer
    For i = 1 To 100000
    LDigit n
    Next i
    Debug.Print Timer - t

    t = Timer
    For i = 1 To 100000
    LargestDigit n
    Next i
    Debug.Print Timer - t
End Sub