I do not know of an integer variable with a minimum of zero, but if there is and you try to set it to a below zero value you wil get an error.
Creating a property wil do it, reading the property will look like this:
Text1 = Form1.myposint
setting the property wil look like this:
Form1.myposint = Text1
the property looks like this:
Dim aPositiveInt As Integer
Public Property Let myposint(new_myposint As Integer)
If new_myposint > -1 Then
aPositiveInt = new_myposint
Else
' Something is trying to give a value lower than 0 take appropriate action
MsgBox "Can`t make the value lower than zero"
End If
End Property
Public Property Get myposint() As Integer
myposint = aPositiveInt
End Property