Vb lecture notes

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Controls:
OptionButtons (RadioButtons):
Multiple choices, but user can select only
one choice
Check Box:
Multiple choices, user can select many
choices
Combo Box:
One option can be selected
List Box:
One option can be selected
Frames:
Provide a way of grouping related controls
on a form. And, in the case of option
buttons, frames affect how such buttons
operate.
To group controls in a frame, you first draw
the frame. Then, the associated controls
must be drawn in the frame. This allows you
to move the frame and controls together.
Image Boxes:
An image box allows you to place graphics
information on a form.
Image box graphics can be resized by using the Stretch property.
Image Box Properties:
Picture Establishes the graphics file to display in the image box.
Stretch If False, the image box resizes itself to fit the graphic. If True, the graphic resizes to fit
the control area.
Drive List Box:
The drive list box control allows a user to select a valid disk drive at run-time. It displays the
available drives in a drop-down combo box. No code is needed to load a drive list box; Visual
Basic does this for us. We use the box to get the current drive identification.
Drive List Box Properties:
Drive Contains the name of the currently selected drive.
Drive List Box Events:
Change Triggered whenever the user or program changes the drive selection.
Directory List Box:
The directory list box displays an ordered, hierarchical list of the user's disk directories and
subdirectories. The directory structure is displayed in a list box.
Like, the drive list box, little coding is needed to use the directory list box – Visual Basic does
most of the work for us.

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Directory List Box Properties:
Path Contains the current directory path.
Directory List Box Events:
Change Triggered when the directory selection is changed.
File List Box
The file list box locates and lists files in the directory specified by its Path property at run-time.
You may select the types of files you want to display in the file list box.
File List Box Properties:
FileName Contains the currently selected file name.
Path Contains the current path directory.
Pattern Contains a string that determines which files will be displayed. For example, using *.jpg
only displays files with the .jpg extension.
Synchronizing the Drive, Directory, and File List Boxes:
The drive, directory, and file list boxes are almost always used together to obtain a file name. As
such, it is important that their operation be synchronized to insure the displayed information is
always consistent.
When the drive selection is changed (drive box Change event), you should update the directory
path. For example, if the drive box is named drvExample and the directory box is dirExample,
use the code:
Dir1.Path = Drive1.Drive
When the directory selection is changed (directory box Change event), you should update the
displayed file names. With a file box named filExample, this code is:
File1.Path = Dir1.Path
Once all of the selections have been made and you want the file name, you need to form a text
string that correctly and completely specifies the file identifier. This string concatenates the
drive, directory, and file name information.
Example code for concatenating the available information into a proper file name and then
loading it into an image box is:
Dim YourFile as String
YourFile = File1.Path + "" + File1.FileName
Image1.Picture = LoadPicture(YourFile)
Note we only use properties of the file list box. The drive and directory box properties are only
used to create changes in the file list box via code.
IF Syntax:
If condition then
Statements
Else
Statements

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End If
Loops:
For…Next Syntax:
For variable=start to end
Statements
Next
By default increment is of 1. For more increment, we write step increment, e.g. step2 for
increment of 2.
While…Wend Syntax:
While condition
Statements
inc/dec
Wend
Example:
num=Text1.Text
start= Text2.Text
end=Text3.Text
inc= Text4.Text
while start<=end
print num +”*”+start+”=”+num*start
start=val(start+inc)
wend
Do…Loop:
Do While…Loop syntax:
Do While(condition)
Statements
Inc/dec
Loop
Example:
Private Sub Command1_Click()
Dim x As Integer
x = 1
Do While x <= 10
Print x
x = x + 1
Loop
End Sub

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Do Until…Loop syntax:
Unlike the Do While...Loop and While...Wend repetition structures, the Do Until... Loop
structure tests a condition for falsity.
Statements in the body of a Do Until...Loop are executed repeatedly as long as the condition is
False.
Do Until(condition)
Statements
Inc/dec
Loop
Example:
Private Sub Command1_Click()
Dim x As Integer
x = 1
Do Until x > 10
Print x
x = x + 1
Loop
End Sub
Message Box:
The message box is used to displays a message
Input Box:
The input box is used to take input
Some Control Events:
Click Event triggered when item in list is clicked.
Text Box Events:
Change Triggered every time the Text property changes.
LostFocus Triggered when the user leaves the text box. This is a good place to examine the
contents of a text box after editing.
Some Control Methods:
Combo Box Methods:
AddItem Allows you to insert item in list.
Clear Removes all items from list box.

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