1. Chapter 8 - Functions and Functionality
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2. Todays lesson is like an episode of the X-files…

3. Todays lesson is like an episode of the X-files…
A lot of your questions will finally be answered…

4. Todays lesson is like an episode of the X-files…
A lot of your questions will finally be answered…
…And a lot will be raised.

5. Chapter 8 is a must-read chapter
It covers the essentials of VB Programming

6. What is a VB Program?
The Visual Basic program code is, for the most part, on long set of event procedures with a Declarations section at the beginning of the code.
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7. This is too much to memorize…
For now, just know where to look it up!

8. Modules
A module is a file that holds procedure code. The file that holds the form and its code is technically called the Form module.
You can add a form or a module by right clicking on the project window.
You can view your project properties by clicking on the “view” menu and choosing “project properties”.
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9. Modules All forms are modules. Modules may also hold only code.
In brief, a module is a large section of related code.
The declarations section appears at the beginning of a module’s code section.
A procedure resides in a module and performs a specific task.

10. Your Project You can manage your project from the project window.
Add/Delete Modules and Forms
Change Views

11. Making a procedure
Go to form view
Click on Tools
Add Procedure

12. 3 types of procedures covered so far
Event Procedures Sections of code that handle occurrences.
Subroutines Sections of code that perform routine processing
Functions Sections of code that return a value.

13. Calling a subroutine Call mySubroutine() mySubroutine()
The first syntax is clearer, so lets use it.

14. Calling an Event Procedure
The computer keeps a constant watch out for events.

15. Calling a function
A function essentially becomes a value and passes that value back to the program.
For instance, an InputBox “becomes” the string someone puts in.
strMyName=InputBox(“Type your Name”)
intX=sqr(16)

16. Scope
Scope is the realm of visibility, or use, of a variable or procedure.

17. Procedures -- Public or Private
Controls (buttons, etc) are always Public
Public Procedures are visible to the entire project
Private Procedures are visible to the current module.
Very analogous to public places and Private places in real life.

18. Variable Scope
Public (or global)
Private (or local)

19. Variable Scope
A local variable can be used only by code to which it is directly visible.
A global variable can be used by code outside its declared area, but not outside its module.
A global variable is visible to other modules in the application if you declare it such: Public gIntMyAge as Integer

20. So a variable has three scope levels:
Private to a subroutine
Module level
And truly global

21. Functions

22. Functions return a value
intDiceRoll=RollDice(6)
Public Function RollDice(intSides as Integer)
Randomize
RollDice=int(rnd()*intSides +1)
End Function
There are actually three functions here -- can you spot the intrinsic functions?

23. Arguments
Arguments are the values passed into a subroutine. In events such arguments may automatically include mouse coordinates, ASCII values, and so on.
Private Sub mySubroutine(intX as Integer, strName as String)
The following call the above subroutine:
Call mySubroutine(intZ, strEmployee)
mySubroutine(5, “Bob”)
The missing Call keyword does not otherwise affect the syntax.

24. Changing Data
Subroutines and Functions can change all the variables because the values are passed “by reference”. That means they refer to the actual memory locations.
If you don’t want the values changed, pass the data “by value” only.
Keywords: ByRef, ByVal
ByRef is the default.

25. Example
Public Sub myStudent (ByRef intGrade as Integer, ByVal strName as String, intFinal as Integer)
What above value(s) can the subroutine change. What above value(s) can it not.

26. Warning! Warning! The default is ByRef
You can change other variables to which you have access--for instance public variables.
Make variables private whenever possible for proper housekeeping and scalability of your program.

27. You can pass an object as an argument.
A control is an object.
Useful under some circumstances

28. Summary Module -- A file containing code
Form Module -- A file containing form generation information and code
Procedure -- A section of code that performs a task
Event Procedure -- A section of code that responds to an occurrence
Subroutine -- A section of code you may call from elsewhere in the program
Function -- A procedure that returns a value
Arguments --The values passed to a subroutine or function

29. Summary
Variable scope can be private, public to the module, or global to the application
Procedures can be private to the module or public to the application.
You may make a module to store procedures. Then the procedures are easily reusable.