3.2.10 - Local variables and modular design (VB.NET)

Lifetime and scope of local variables

A local variable belongs to one executing subroutine instead of being shared throughout the program.

Function AddBonus(ByVal score As Integer) As Integer
    Dim result As Integer = score + 2
    Return result
End Function

Sub Main()
    Dim result As Integer = 99
    Dim changed As Integer = AddBonus(6)
    Console.WriteLine(changed)
    Console.WriteLine(result)
End Sub

The outputs are 8 and 99. The function's local result is distinct from Main's local result, even though the names match. Main receives the number 8 through the return, not direct access to the function's variable. A later call with score 1 creates its own result 3; it does not continue from the previous 8. Ordinary locals are not persistent stored history.

Scope is where a name can be accessed; lifetime is when its storage exists. A local declared inside a narrower VB.NET block, such as an If body, also has that narrower scope. Use local intermediates to prevent other routines from accidentally changing them and to reduce hidden dependencies. A module-level shared variable can be accessed by several routines and may retain a change, so using it where a local suffices makes reasoning and testing harder.

Optional Python demonstration — two calls, separate state. Predict then run. Change the second call from 1 to 10 and check that the outer result 99 still does not change.