1. Chapter 7: Using Functions, Subs, and Modules
Introduction to Programming with Visual Basic 6.0 by McKeown and Piercy

2. Plan for Revising Vintage Videos Application
Need a way of adding videos to system
Need a better way of managing membership list
Need capability to add late fees to customer’s bill
Need a system to print alphabetical list of members or videos
Introduction to Programming with Visual Basic 6.0 by McKeown and Piercy

3. Design for Expanded Vintage Videos Project
Introduction to Programming with Visual Basic 6.0 by McKeown and Piercy

4. Membership Management Form
Introduction to Programming with Visual Basic 6.0 by McKeown and Piercy

5. Modified Videos Form
Introduction to Programming with Visual Basic 6.0 by McKeown and Piercy

6. Using General Procedures
Event procedures are associated with a particular event and are not usually available to other forms.
General procedures are used for specific tasks that are not associated with an event.
General procedures are defined in the General Object of a form and then invoked elsewhere in the project.
Two types of general procedures:
subs (subroutines)
functions
Introduction to Programming with Visual Basic 6.0 by McKeown and Piercy

7. Relationship Between General and Event Procedures
Introduction to Programming with Visual Basic 6.0 by McKeown and Piercy

8. Subs and Functions
A sub is a unit of code that performs a specific task but returns no value.
A function is similar to the built in functions in that arguments are passed to it and processed to compute a single value returned by its name.
Introduction to Programming with Visual Basic 6.0 by McKeown and Piercy

9. Primary Purposes of Subs and Functions
Introduction to Programming with Visual Basic 6.0 by McKeown and Piercy

10. Working with General Procedures
General procedures must be created and then invoked.
Invoking a function:
variable = functionname(arg1, arg2, …, argn)
Invoking a sub:
subname arg1, arg2, …, argn
Introduction to Programming with Visual Basic 6.0 by McKeown and Piercy

11. Creating Subs and Functions
To create a sub or function you can
Use the Tools|Add Procedure menu command and select the type of procedure to add or
simply type the word Sub or Function and press Enter after any existing event or general procedure.
In either case, then add the parameters.
Introduction to Programming with Visual Basic 6.0 by McKeown and Piercy

12. Creating a Function
The general form of the function definition statement is:
Function FuncName(parameter1 as type, parameter2 as type, …) as type
For example
Function intFindMax(intNum1 as Integer, intNum2 as Integer) as Integer
An important rule is that the name of the function must be assigned a value in the function.
Introduction to Programming with Visual Basic 6.0 by McKeown and Piercy

13. Creating a Sub The general form of the sub definition statement is:
Sub SubName (parameter1 as type, parameter2 as type, …)
Note that the sub name is not assigned a data type
Example
Sub Reverse(curFirst as Currency, curSecond as Currency)
Introduction to Programming with Visual Basic 6.0 by McKeown and Piercy

14. Relationship Between Sub Definition Statement and Statement Invoking the Sub
Introduction to Programming with Visual Basic 6.0 by McKeown and Piercy

15. Relationship Between Function Definition Statement and the Statement Invoking the Function
Introduction to Programming with Visual Basic 6.0 by McKeown and Piercy

16. Matching Arguments and Parameters
For both sub and functions, the number and type of arguments in the invoking statement must match the number and type of parameters in the procedure definition statement.
In both the argument and parameter list, fixed-size arrays are referenced by the name of the array followed by parentheses.
Introduction to Programming with Visual Basic 6.0 by McKeown and Piercy

17. Function to Compute Income Taxes
Public Function curComputeTaxes(intNumDep As Integer, _
curGrossIncome As Currency) as Currency
Dim curTaxIncome As Currency
curTaxIncome = curGrossIncome intNumDep * 2650
Select Case curTaxIncome
Case Is <= 24650
curComputeTaxes = 0.15 * curTaxIncome
Case Is <= 59750
curComputeTaxes = * (curTaxIncome )
Case Is <=
curComputeTaxes = * (curTaxIncome )
Case Is <
curComputeTaxes = * (curTaxIncome )
Case Else
curComputeTaxes = * (curTaxIncome )
End Select
End Function
Introduction to Programming with Visual Basic 6.0 by McKeown and Piercy

18. Sub to Reverse Two Values
Sub Reverse(curFirst as Currency, curSecond as _
Currency)
Dim curTemp as Currency
curTemp = curFirst
curFirst = curSecond
curSecond = curTemp
End sub
Introduction to Programming with Visual Basic 6.0 by McKeown and Piercy

19. Sub to Sort Arrays Public Sub Sort(curFirstList() As Currency, _
curSecondList()As Currency, intNumList As Integer)
Dim blnNoReversal As Boolean, intCounter As Integer
blnNoReversal = False
Do Until blnNoReversal
blnNoReversal = True
For intCounter = 0 To intNumList - 2
If curFirstList(intCounter ) > _
curFirstList(intCounter + 1) Then
Reverse curFirstList(intCounter ), _
FirstList(intCounter + 1)
StrReverse curSecondList(intCounter ), _
curSecondList(intCounter +1)
End If
Next
Loop
End Sub
Introduction to Programming with Visual Basic 6.0 by McKeown and Piercy

20. Global Declarations and the Code Module
In a global declaration, the scope of global variables, as compared to form-level variables or procedure-level variables, includes all parts of the project.
The Code Module is the section of pure code that is known to all parts of the project.
Use Public statement to declare variables
Public varName1 as type, varName2 as type, ...
Introduction to Programming with Visual Basic 6.0 by McKeown and Piercy

21. Scope of Global Variables
Introduction to Programming with Visual Basic 6.0 by McKeown and Piercy

22. Use of String Functions
Len(string) --returns number of characters in string.
Left(string, N) or Right(string, N) --returns the leftmost or rightmost N characters in a string.
Mid(String,P,N) --returns N characters in a string starting at Pth character.
LTrim(string) or RTrim(string) --trims blank characters from left (right) end of string.
Introduction to Programming with Visual Basic 6.0 by McKeown and Piercy

23. Passing by Value in Subs
If there is a two-way communication between arguments and parameters, then you have passing by reference.
If there is a one-way communication between arguments and parameters, then you have passing by value.
It is possible to force passing by value by adding the keyword ByVal prior to a variable in the procedure definition statement.
Introduction to Programming with Visual Basic 6.0 by McKeown and Piercy