Decisions & loops

Express decisions directly and stop loops at a clearly defined boundary.

Use an early guard for invalid input#

An If condition should describe the decision, not the desired screen text. The Greeting example in procedures rejects an empty normalized name before the success path. That order prevents a success message from briefly appearing for invalid input.

Select one named case#

LanguageWorkbench / Main.bas · StateCaption

Public Function StateCaption(ByVal state As TaskState) As String
    Select Case state
        Case TaskState.Ready
            StateCaption = "Ready"
        Case TaskState.Running
            StateCaption = "Working"
        Case Else
            StateCaption = "Complete"
    End Select
End Function

TaskState is an Enum declared in the same module. The caller uses names such as TaskState.Running instead of unexplained integer codes. Case Else gives the remaining path a deliberate result.

Keep the enum declaration with the example#

Main.bas · file scope, outside procedures

Public Enum TaskState
    Ready = 0
    Running = 1
    Complete = 2
End Enum

A public enum in a standard module can be shared. Name its members for states, not for labels that may change in the UI.

Make loop progress visible#

LanguageWorkbench / Main.bas · CountDown

Public Function CountDown(ByVal start As Long) As Long
    Dim value As Long
    value = start
    Do While value > 0
        value = value - 1
    Loop
    CountDown = value
End Function

CountDown(3) returns 0. The loop updates the same variable its condition tests. A start value of zero or a negative value skips the body and returns that start value; it is not silently clamped.

Choose the right loop for the data#

Use a counted For loop when positions matter, and read array bounds with LBound/UBound. Use For Each for values in a supported collection. JSON arrays and Recordsets have their own zero-based access APIs; a Collection’s positions are one-based. Do not transfer an indexing assumption between them.

Test the branch, not only the happy path#

For each decision, write down an input that takes each branch. For a loop, test zero iterations, one iteration and several. The debugging exercise intentionally reverses a condition to demonstrate why a successful Check does not prove your rule is correct.

Source baseline 20f4bfed6b · Build manifest

Sources & maintenance

Original web explanation, reviewed against these repository sources. API tables and example files follow the implementation.

docs/manual/21-language-reference.md
docs/manual/11-language-toolkit.md
site/examples/LanguageWorkbench/Main.bas