1. CSCI 3327 Visual Basic Chapter 6: Methods: A Deeper Look
UTPA – Fall 2011
Part of the slides is from Dr. John Abraham’s previous lecture slides. – Xiang Lian

2. Objectives In this chapter, you will:
Explore the components of a module or a class
Get familiar with the syntax of methods
Learn the declaration of methods
Subroutines
Functions
Become aware of .Net Namespace
Discover how to use recursions

3. Modules, Classes and Methods
Modules and classes make up a program
Modules and classes are composed of smaller pieces called methods, instance variables and properties
Related classes are grouped into namespaces
Two types of methods exist:
Subroutines
Functions

4. Pre-Packaged and User Defined
.NET framework provides a class library that contains many pre-packaged classes:
Mathematical calculations, error checking, GUI & graphics, String and character manipulations, I/O operations, XML, database, web, etc.
Users can define their own classes
You can combine new modules and classes with pre-packaged ones

5. Method Basics A method is invoked by a method call
Method call specifies the method name and provides information as arguments
When method is finished the control goes back to the caller
The method may or may not return results
Method provides for divide-and-conquer approach to software engineering
Methods can be used over and over again

6. Methods That Do Not Return a Value
Methods that only performs a task such as printing, but do not return a value
These methods are generally called Subroutines
The parameters passed into these methods are ByVal parameters.

7. Declaring a Subroutine
Sub methodName (parameterList)
Declarations and statements
End Sub
If you pass a parameter ByRef and if the value of that parameter is changed by the subroutine, that variable’s value also will be changed in the calling module

8. Methods That Return A Value (Functions)
Functions must have a return statement followed by what is being returned
Declared as follows:
Function Square(ByVal v As Integer) As Integer
Return v^2
End function
Please pay attention to the type in the last portion of function heading

9. Shared Methods Methods declared in a module are shared by default
If you want to share a method in a class, use the modifier Shared in the header of the method (instead of private or public) – write and writeline are shared methods
Class Math contains many shared methods

10. Subroutines A Method that does not return a value
Pass values in and out through interfaces, ByVal/ByRef parameters
ByVal
A copy is passed
May pass actual values rather than variables
Original value is not changed
ByRef
Memory location is passed
Value stored in that location may change
Cannot pass a value, must pass a variable
Side effects may occur

11. Functions Returns exactly one value through its name
Name must have an associated type

12. .Net Namespaces System.windows.forms System.io System.Data
Contains the classes required to create and manipulate GUIs
System.io
Contains classes that enable programs to input and output data
System.Data
Contains classes that enable program to access and manipulate databases
There are many others

13. Recursion A method calling itself
The method only knows how to solve the simplest case (base case)
A more complex case is divided into two pieces, one base case and remaining as a complex case
Factorial of 5 is 5 times factorial of 4.
Factorial of 1 is 1 (base case)

14. See Recursion Examples

15. Method Overloading
Multiple methods with the same name but different signatures
Meaning different numbers and types of parameters OR different ordering of parameters by type
Function square(ByVal value As Integer) As Integer
Return convert.toInt32(value ^ 2)
End Function
Function square(ByVal value As Double) As Integer
Return value ^ 2

16. More Examples (Optional Parameters)
May have one or more optional parameters (list after the required parameters)
Specify default value in case not passed in
Function Power(ByVal base As Integer, Optional ByVal exponent As Integer =2) As Integer
Dim total As Integer =1
For i As Integer = 1 To exponent
total *=base
Next
Return total
End Function