tutorial 7: sub and function procedures1 tutorial 7 sub and function procedures
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Tutorial 7: Sub and Function Procedures 1
Tutorial 7Sub and Function Procedures
Tutorial 7: Sub and Function Procedures 2
Creating Sub and Function ProceduresLesson A Objectives
After completing this lesson, you will be able to:
Explain the difference between a Sub procedure and a Function procedure
Create a procedure that receives information passed to it
Explain the difference between passing data by value and by reference
Create a Function procedure
Tutorial 7: Sub and Function Procedures 3
Procedures
A procedure is a block of program code that performs a specific task
Procedures in Visual Basic .NET can be either Sub procedures or Function procedures
Function procedures return a value after performing their assigned task
Sub procedures do not return a value
Tutorial 7: Sub and Function Procedures 4
Sub Procedures
Event procedures
Called by Visual Basic .NET in response to an event
Every event procedure has at least two parameters
• sender – the object that raised the event
• e – information about the object
User-defined procedures
You must call explicitly
You can define parameters
Tutorial 7: Sub and Function Procedures 5
Event Procedures
Private Sub ExitButton_Click(ByVal sender As Object, _
ByVal e As System.EventArgs) _
Handles ExitButton.Click
Me.Close()
End Sub
Parameters
Tutorial 7: Sub and Function Procedures 6
Including Parameters in a User-Defined Sub Procedure
User-defined Sub procedures have both a procedure header and procedure footer
Accessibility Sub ProcedureName([ParameterList])
‘ Statements in the procedure
End Sub
Private Sub CalculatePay(ByVal sngHours As Single, _
ByVal sngRate As Single, ByRef sngPay As Single)
‘ Calculate the pay from hours and rate of pay
sngPay = sngRate * sngHours
End Sub
Call CalculatePay(35.9, 95, sngPay)
Tutorial 7: Sub and Function Procedures 7
Passing Variables
Pass by value – make a copy of the data Use ByVal before the parameter name This is the default if you do not specify
Pass by reference – pass the address of the data Use ByRef before the parameter name
Private Sub CalculatePay(ByVal sngHours As Single, _
ByVal sngRate As Single, ByRef sngPay As Single)
‘ Calculate the pay from hours and rate of pay
sngPay = sngRate * sngHours
End Sub
sngHours = 35.9: sngRate = 95.0
Call CalculatePay(sngHours, sngRate, sngPay)
Tutorial 7: Sub and Function Procedures 8
Function Procedures
A Function procedure, typically referred to as a function, is a block of code that performs a specific task
You can also create your own functions, referred to as user-defined functions, in Visual Basic .NET
The Return statement alerts the computer that the function has completed its task and ends the function after returning the value of its expression
Tutorial 7: Sub and Function Procedures 9
Function Procedures
Accessibility Function FunctionName([ParameterList]) As DataType
‘ Statements in the procedure
Return SomeData
End Function
Private Function CalculatePay(ByVal sngHours As Single, _
ByVal sngRate As Single) As Single
‘ Calculate the pay from hours and rate of pay
Return sngRate * sngHours
End Function
sngHours = 35.9: sngRate = 95.0
sngPay= CalculatePay(sngHours,sngRate)
Tutorial 7: Sub and Function Procedures 10
Using a List Box ControlLesson B Objectives
After completing this lesson, you will be able to:
Add a list box to a form
Add items to a list box
Sort the contents of a list box
Select a list box item from code
Determine the selected item in a list box
Code a list box’s SelectedValueChanged event
Tutorial 7: Sub and Function Procedures 11
Adding a List Box to a Form
You can use a list box control to display a list of choices from which the user can select zero choices, one choice, or more than one choice
The number of choices the user is allowed to select is controlled by the list box control’s SelectionMode property
The Windows standard for list boxes is to display a minimum of three selections and a maximum of eight selections at a time
Tutorial 7: Sub and Function Procedures 12
Adding Items to a List Box
The items in a list box belong to a collection called the Items collection
The first item in the Items collection appears as the first item in the list box
The second item appears as the second item in the list box, and so on
The first item in the Items has an index of zero
The second item has an index of one, and so on
Tutorial 7: Sub and Function Procedures 13
Adding Items to a List Box
You use the Items collection’s Add method to specify the items you want displayed in a list box control
When you use the Add method to add an item to a list box, the position of the item in the list depends on the value stored in the list box’s Sorted property
Tutorial 7: Sub and Function Procedures 14
The SelectedItem and SelectedIndex Properties
A list box’s SelectItem property and its SelectedIndex property can be used both to determine the item selected in the list box and to select a list box item from code
The selected item is also called the default list box item
Should be either the most used selection
Or, if all of the selections are used fairly equally, the first selection in the list
Tutorial 7: Sub and Function Procedures 15
Coding the GetFwtTax Function
The amount of federal withholding text (FWT) to deduct from an employee’s weekly gross pay is based on the employee’s filing status—either single, (including head of household) or married—and his or her weekly taxable wages
To calculate the federal withholding tax you need to know the employee’s
Gross pay amount
Marital status
Number of withholding allowances
Tutorial 7: Sub and Function Procedures 16
Completing the CalculateButtonClick Event Procedure
Now that you have created the GetFwtTax
function, you can call the function from
the CalculateButton Click event procedure
Tutorial 7: Sub and Function Procedures 17
Clearing the Contents of the Label Controls
The label controls also should be cleared when the SelectedValueChanged event occurs for one of the list boxes in the interface
A list box’s SelectedValueChanged event occurs each time a different value is selected in the list box
Tutorial 7: Sub and Function Procedures 18
Completing the Payroll ApplicationLesson C Objectives
After completing this lesson, you will be able to:
Add an existing form to a solution
Add a new module to a solution
Code the Sub Main Procedure
Create an instance of a form
Display a form object using the ShowDialog method
Tutorial 7: Sub and Function Procedures 19
Adding an Existing Form to a Solution
The Copyright screen is to be the splash
screen for each custom application
created by the company
Tutorial 7: Sub and Function Procedures 20
Coding the Sub Main Procedure
Sub Main is a special procedure in Visual Basic .NET, because it can be declared as the “starting point” for an application
In other words, you can tell the computer to process the Sub Main procedure automatically when an application is started
You enter the Sub Main procedure in a module, which is a file that contains code that is not associated with any specific object in the interface
Tutorial 7: Sub and Function Procedures 21
Creating an Instance of a Form
A class definition specifies (or defines) the attributes and behaviors of an object
When an application is started, Visual Basic .NET automatically processes the code contained in one object: the Startup object
Similarly, if the PayrollForm is specified as the Startup object, Visual Basic .NET automatically processes the code contained in the PayrollForm class definition
When the Sub Main procedure is the Startup object, as it is in this case, neither the CopyrightForm class definition nor the PayrollForm class definition will be processed automatically
Tutorial 7: Sub and Function Procedures 22
Using a Form Object’s Show Dialog Method
The form object’s Show dialog method allows you to display a form object on the screen
The syntax of the ShowDialog method is form.ShowDialog(), where form is the name of the object variable that contains the form object’s address