Reference paremeters

Option VBASupport 1
Option Explicit

Sub Main
    Dim y As Double

    y = 10
    halve1 y
    MsgBox " y = " & y
End

Sub halve1(ByVal x As Double) 'copies the value of y into x but doesn't change the value of x
    x = x/2
End Sub

Sub halve2(ByRef c As Double) 'x as the re3ference but changes the value of y
    x = x/2
End Sub