Chapter 8 - Functions and Functionality 092600

Todays lesson is like an episode of the X-files…

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

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.

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

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. p. 216

This is too much to memorize… For now, just know where to look it up!

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”. p116

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.

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

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

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.

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

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

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)

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

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.

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

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

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

Functions

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?

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.

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.

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.

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.

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

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

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.