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To type the VB code behind the command button (named cmdPush), Double-Click on the Push Me
(caption) command button
As a result the Visual Basic Code Window will open, with the First and Last lines of the Sub Procedure
already in place, by default within VB
Follow good coding conventions and Indent all lines between Private Sub and End Sub
Label Caption Property
A Label control’s caption size is unlimited. For forms and all other controls that have captions, the limit is 255 characters.
Variables: Memory locations that hold data, that can be changed during project execution
(eg: student names will vary as the information for each student is being processed)
Constants: Memory locations that hold data that cannot change during execution
(eg: however, the college which the students attend (UCC) will remain the same)
Variables and Constants
Variables are declared, depending on where they are used and how long their value needs to be retained
Variables are locations in the computers memory, which are named by the user
Variables store values
The values which are assigned to variables can change during project execution (the values they hold varies, hence the name)
Variables
Variables have to be declared (the computer must be made aware of their existence) and once they have been declared, the computer allocates them (memory) storage space and assigns this area of memory a name, called an identifier
Variables are declared using the DIM statement
DIM Variable Name (Identifier) AS Data Type
The declaration statements establish the project variables, assign names to the variables, and specify the type of data that the variables will hold
The statements are non-executable (they are not executed in the flow of instructions during program execution
Dim stName As STRING (Declares a string variable)
Dim iCounter As INTEGER (Declares an integer variable)
The reserved word DIM is short for dimension, meaning size Variables can have a number of different data types
A variable can only store values which correspond with the data type they are assigned
The data type of a variable indicates what type of information will be stored in the allocated memory space
The default data type is variant
The advantage of using variant data type is that it is easy, and the variables change their appearance as needed for each situation
The disadvantage is that variants are less efficient than the other data types, they require more memory and operate less quickly
Data Types
DIM Variable name (Identifier) AS Data Type
Dim iYear As IntegerDim stCustName As String
can also be declared as:
Dim iYear As Integer, stCustName As String
Also Specific Characters can be used to represent each of the Data Types
Variable Declarations
- String ($)- Integer (%)- Currency (@)- Long Integer (&)- Single Precision (!)- Double Precision (£)
Variable Declarations
Dim iYear%, stCustName$, cInterest@
Data Types
Text Box controls are used when users are required to type some input (during program execution), or output is displayed on the form (known as the user-interface when the project is running)
To display some text in a Text Box during program execution, assign a literal to the Text Property of the Text Box (Does not have a CAPTION Property)
txtMessage.Text = “Hello World”
Text Boxes
In this example, whatever the user enters into the Text property of the Text Box (txtName) is assigned
to the Caption property of the Label (lblName)
lblName.Caption = txtName.Text
Frames are used as containers for other controls
Groups of Option Buttons or Check Boxes can be placed in frames
Using frames to group controls makes the forms easier to understand
Set a Frames Caption Property to display the words on the user-interface, on the top edge of the Frame
Frames
Allows the user to select or deselect an option
In a group of Check Boxes, any number of them may be selected
The Value property of a Check Box is set to 0 if unchecked, 1 if checked, or 2 if disabled (greyed)
0 = vbUnchecked1 = vbChecked
Check Boxes
Use only when one Option of a group maybe selected
Any Option Buttons placed directly on a Form, function as a Form Group
A group of Option Buttons inside a Frame function together as a Frame Group
The Value property of an Option Button is set to True if selected, or to False if unselected
Option Buttons
Images
An Image control holds a picture
An Images Picture property can be set to a file with an extension of .BMP, .GIF, .JPG
Writing Windows Apps. with VB• The Windows GUI
Text boxes
Frame
Labels
Option buttons
Check boxes
Command buttons
Image
Picture box
We want to create a program where the height property value of a text box is displayed in the text box, while further printing the contents of the text box
onto the form
A Practical Example (using Text Boxes)
A variable (X) is declared as an integer Data Type, meaning it can only accept numeric values
The Text Box is named BoxContents
The Variable X is assigned the value of the Height property of BoxContents (Text Box)
The Text property of BoxContents consists of a literal and the value of the variable X
The Text in BoxContents is also printed on the form
Additional Instructions
Make the Text Box blank once the contents have been printed
Notify the user that the Text Box is blank
Add this Code to the End of the Sub-Procedure
BoxContents.Text =“”‘Empties whatever is in the text box
Print “The Text Box (BoxContents) is now blank”‘Prints this message on the form