Ch 10: More on Variables and Subroutines CP212 Winter 2012

Topics Subroutines Functions Modular programming o 3 Main Benefits Variable and Subroutine Scope Using and Passing Parameters Module level "Global" variables Passing arrays The Workbook_Open event handler Generating Random Numbers (Ex. 10.4)

Scope A variable is created in a sub can only be used in that sub. It has limited scope: sub-level scope. Known as a local variable. Sub myFirstSub() Dim score As Integer score = 3 Msgbox score End Sub Sub mySecondSub() Dim score As Integer score = 4 Msgbox score End Sub Different variables, different location in memory.

Module-Level Scope If you want subs to share a variable, declare it outside of a sub This makes it a module-level variable Every sub in the module can access the variable Option Explicit Dim userName As String Sub myFirst() userName = “Biff” End Sub Sub mySecond() Msgbox userName End Sub

Visibility Levels Keywords such as Public or Private are used to indicate their visibility, aka, their scope. userName has project-level scope, all modules can access it income has Module Level scope - only accessed in this module. This is the same as Private. To limit visibility to subs in Module1, use "Private" instead of "Public". Private - good for "helper" subs that have limited use or will only be called by subs in that module

Visibility Levels Using Public makes variable available to the entire Project (all modules) Using Dim outside of subroutines makes Module-Level Scope (same as Private). Subroutines can be either Public or Private as well.

Visibility Levels See Scope in Chapter10ExamplesXXXX2012.xlsm

Modularity break down a large problem into smaller ones each subroutine should handle a small, complete problem a program then consists of many subroutines and functions each sub can call other functions or subs Sub MainProgram() ' The main program calls other subs Call GetInput Call ProcessData Call DisplayResults End Sub The keyword CALL is optional, but it helps illustrate what is going on.

3 Benefits of Modular Programming Easier to read Easier to debug Software reuse Ch10 shows how the Travelling Salesperson program from the last chapter has been broken down into smaller subroutines.

A Modular Program modularity.xls in MyLearningSpace Option Explicit ' Project level variables Public userName As String Public Sub MainProgram() GatherData ProcessTheMessage DisplayGreeting End Sub Private Sub GatherData() userName = InputBox("What is your name?", "Greetings", "-user-") End Sub Private Function Greeting(s As String) As String Greeting = "Hello there, " & s End Function Private Sub ProcessTheMessage() MsgBox "The length of the message is now " & _ Len(Greeting(userName)) & " characters.", _ vbOKOnly + vbInformation, _ Title:="Results" End Sub

Passing Arrays pretty important, don't let the () mess you up Write a subroutine that will sort an array of any size Sub CallingSub() Dim names(100) As String For i = 1 to 100 names(i) = Range("Names").Cells(i).Value Next SortNames names '<---- Pass the array to the another sub ' Call SortNames(names) ' can also be used End Sub

The Sub Sub SortNames(names() As String) Dim nNames As Integer nNames = UBound(names) ' determines the upper index limit ' More sorting code goes here End Sub UBound returns the largest index of the array, ie: ArraySize - 1 if using 0 based arrays (the default) Can also use LBound to determine the lowest bound for the array

3 Minute Challenge Write a subroutine that takes an array of any size and prints all the values. Take 3 minutes. GO! Solution on next slide.

Using LBound and UBound Sub PrintArray(theArray() As String) Dim i As Integer ' Safer to check LBound and UBound ' in case there is Base 0 or Base 1 confusion For i = LBound(theArray) To UBound(theArray) MsgBox theArray(i) Next End Sub

Function Subroutines Function CircleArea (r As Single) As Single If r > 0 Then CircleArea = * r * r Else CircleArea = 0 End If End Function Can be used in VBA and in the Spreadsheet like a built-in function If saved to personal.xlsb, you'll have to call it with =personal.xlsb.CircleArea(A5)

Generating Random Numbers See Example Functions.xlsm use Application.Volatile to ensure that different values are calculated each time the sheet recalculates o matches the operation of the RAND spreadsheet function VBA RND function generates a value between 0 and 1 with a uniform distribution

Workbook_Open Event Handler code placed in this subroutine runs when the workbook is opened not placed in a Module, its placed in the ThisWorkbook code window lots of other Workbook events worth exploring

References For more details, check out: Recommended Exercises Chapter , 3, 4, 6, 8, 15, 16, 19