Chapter 3 - Visual Basic Schneider Chapter 3-A Fundamentals of Programming in Visual Basic.
-
Upload
erin-marsh -
Category
Documents
-
view
291 -
download
2
Transcript of Chapter 3 - Visual Basic Schneider Chapter 3-A Fundamentals of Programming in Visual Basic.
Chapter 3 - Visual Basic Schneider
Chapter 3-A
Fundamentals of Programming in
Visual Basic
Chapter 3 - Visual Basic Schneider
Outline and Objectives
Visual Basic Objects Visual Basic Events
Numbers Strings Input/Output Built-In Functions
Chapter 3 - Visual Basic Schneider
The Initial Visual Basic Screen
Toolbox
Project Explorerwindow
Properties window
Form
Menu bar
Description pane
Form Layout window
Toolbar
Project Container window
Chapter 3 - Visual Basic Schneider
Steps to Create a Visual Basic Program
1. Create the interface by placing controls on the form
2. Set properties for the controls and the form
3. Write code for event procedures associated with the controls and the form
Chapter 3 - Visual Basic Schneider
Four Useful Visual Basic Controls
Text Boxes Labels
Command Buttons Picture Boxes
Chapter 3 - Visual Basic Schneider
Placing a Text Box on a Form
Double-click on the text box icon in the toolbox to add a text box to your form
Activate the properties window (Press F4)
Set values of properties for text box
Chapter 3 - Visual Basic Schneider
Placing a label on a Form
Chapter 3 - Visual Basic Schneider
Some Useful Properties of Objects
Name
Caption Text (for Text Boxes) BorderStyle Visible BackColor Alignment Font
Chapter 3 - Visual Basic Schneider
Naming Objects:
Use the Property window to change the Name property of an object
Good programming practice dictates that each object name begins with a three letter prefix that identifies the type of object.
Chapter 3 - Visual Basic Schneider
Naming Objects:
Object Prefix Example
Command Button cmd cmdStart
Form frm frmPayroll
Label lbl lblName
Picture box pic picClouds
Text box txt txtAddress
Naming Objects
An Object Name•Must Start with a letter
•Can include numbers and underscore (_)
•Cannot include punctuation or spaces
•Can be a maximum of 40 characters
Chapter 3 - Visual Basic Schneider
Chapter 3 - Visual Basic Schneider
Visual Basic Events
Code is a set of statements that instruct the computer to carry out a task.
Code can be associated with events When an event occurs, the code
associated with that event (called an Event Procedure) is executed.
Chapter 3 - Visual Basic Schneider
Creating An Event Procedure
Double-click on an object to open a Code window. (The empty default event procedure will appear. Click on the Procedure box if you want to display a different event procedure.)
Write the code for that event procedure.
Chapter 3 - Visual Basic Schneider
Example of An Event Procedure
Private Sub objectName_event ( ) statementsEnd Sub
Private Sub Text2_GotFocus( ) Text2.Font.Size = 12 Text2.Font.Bold = False
Text2.forecolor=vbRedEnd Sub
Chapter 3 - Visual Basic Schneider
More Examples
Private Sub cmdButton_Click( ) txtBox.ForeColor = vbRed txtBox.Font.Size = 24 txtBox.Text = “Hello”End Sub
Exercises: What is wrong??!
Chapter 3 - Visual Basic Schneider
A. Private Sub cmdButton_Click( )
frmHi= “Hello”
End Sub
B. Private Sub cmdButton_Click( )
txtOne.ForeColor= “red”
End Sub
Exercises: What is wrong??!
Chapter 3 - Visual Basic Schneider
C. Private Sub cmdButton_Click( )
txtBox.Caption = “Hello”
End Sub
D. Private Sub cmdButton_Click( )
txtOne.MultiLine= True
End Sub
Tips
Most Properties can be set or altered at run time with code.
cmdButton.visible = False The MultiLine property of a text box
can only be set from the properties window, also the Name property….
“” surrounds Caption, Name, Font.Name or strings. Not True for vars or numeric constants
Chapter 3 - Visual Basic Schneider
Color Constants
Chapter 3 - Visual Basic Schneider
• At design time colors are selected from a palette
• At run time the eight most common colors can be assigned with the color constants:
vbBlack vbMagentavbRed vbCyanvbGreen vbYellowvbBlue vbWhite
Chapter 3 - Visual Basic Schneider
Components of Visual Basic Statements
Constants Variables Keywords (reserved words)
Chapter 3 - Visual Basic Schneider
Constant
Can NOT change during the execution of a program.
Types of Constants:•numeric constants
•string constants
Chapter 3 - Visual Basic Schneider
Valid Numeric Constants:
Integer Real number
-2987 -1900.05
16 0.0185
5 10.56
Chapter 3 - Visual Basic Schneider
Invalid Numeric Constants:
14,005.5 6.8% 33- $190.04 15 78 3.5&
Chapter 3 - Visual Basic Schneider
Arithmetic Operations
Operator Operation Basic expression
^ Exponentiation A ^ B
* Multiplication A * B / Division A / B + Addition A + B - Subtraction A - B
Scientific Notation
Chapter 3 - Visual Basic Schneider
10n=1000...0103=1000
10-n=0.000...01 10-3=0.0001
b.10±r VB Notation bE±r
1.4 * 10-45
14 * 10 ^-45
1.4E -45 1.4E -44
Chapter 3 - Visual Basic Schneider
String Constants:
A sequence of characters treated as a single item
The characters in a string must be surrounded by double quotes (“ ”)
Chapter 3 - Visual Basic Schneider
Valid String Constants
“A rose by any other name”“9W”“134.23”“She said, ‘stop , thief!’ ”
Chapter 3 - Visual Basic Schneider
Invalid String Constants
‘Down by the Seashore’“134.24“She said, “Stop, thief!””
Chapter 3 - Visual Basic Schneider
Variables
A storage location in main memory whose value can be changed during program execution.
These storage locations can be referred to by their names.
Every variable has three properties: a Name, a Value, and a Data Type.
Types of variables: Numeric and String
Chapter 3 - Visual Basic Schneider
Rules for Naming Variables
Must begin with a letter Must contain only letters, numeric
digits, and underscores ( _ ) Can have up to 255 characters VB is insensitive for uppercase or
lowercase Cannot be a Visual Basic language
keyword (for example, Sub, End, False)
Chapter 3 - Visual Basic Schneider
Valid Variable Names:
timeElapsed a1b2c3 Var_1 n celsius
Chapter 3 - Visual Basic Schneider
Invalid Variable Names:
maximum/average 1stChoice square yard Name?
Chapter 3 - Visual Basic Schneider
Keywords
Words that have predefined meaning to Visual Basic .
Can Not be used as variable names. Examples:
•End - Print
•Sub - Let
•If -Select
•While -Call
Chapter 3 - Visual Basic Schneider
Numeric Variables
Used to store numbers Value is assigned by a statement of the
form:
numVar = expression
The variable must be on the left and the expression on the right.
Chapter 3 - Visual Basic Schneider
Assignment Statement:
The statement var = expr assigns the value of the expression to the variable
tax = 0.02 * (income - 500 * dependents)
sum = 2 + x + 4.6 + y
Chapter 3 - Visual Basic Schneider
Valid Assignment Statements
count = count + 1 num = 5 count = count + num /2
Chapter 3 - Visual Basic Schneider
Invalid Assignment Statements
10 = count count + 1 = count
Chapter 3 - Visual Basic Schneider
String Variables
A string variable stores a string. The rules for naming string variables
are identical to those for naming numeric variables.
When a string variable is first declared, its value is the empty string.
Chapter 3 - Visual Basic Schneider
Visual Basic Print Statement
Print is a method used to display data on the screen or printer.
Can be used to display values of variables or expressions
Chapter 3 - Visual Basic Schneider
Examples of Print Statements
Private Sub cmdCompute_Click()
picResults.Print 3 + 2 picResults.Print 3 - 2 picResults.Print “3 * 2” picResults.Print 3 / 2 picResults.Print 3 ^ 2 picResults.Print 2 * (3 +
4)End Sub
Chapter 3 - Visual Basic Schneider
Examples of Print Statements
speed=3taxRate=speed+5total=30picOutput.Print speedpicOutput.Print taxRatepicOutput.Print “Class average is”; total/3
3
8
Class average is 10
Chapter 3 - Visual Basic Schneider
Examples of Print Statements
x = 15 y = 5picOutput.Print (x + y) / 2, x / y
Output: 10 3
Chapter 3 - Visual Basic Schneider
String Variable Example
Private Sub cmdShow_Click() picOutput.Cls phrase = "win or lose that counts." picOutput.Print "It's not whether you ";
phrase picOutput.Print "It's whether I "; phraseEnd Sub
Chapter 3 - Visual Basic Schneider
Concatenation
Two strings can be combined by using the concatenation operation.
The concatenation operator is the ampersand (&) sign.
Example
&: is always used to make concatenation
+: makes concatenation when it is used with strings, and as summation with numbers
What about “hi”+5 ???
Chapter 3 - Visual Basic Schneider
Examples of Concatenation:
strVar1 = “Hello”strVar2 = “World”picOutput.Print strVar1& strVar2
txtBox.Text = “32” & Chr(176) & “ Fahrenheit”
Chr() & Asc()
The characters have numbers associated with them, these values called ANSI values of characters
Chr(65) = A Chr(66) = B Chr(97) = a Chr(176) =
•Asc(A) = 65•Asc(B) = 66•Asc(a) = 97•Asc( ) = 176
48
Val, Str Val (“23”) = 23 Val (23) =23 Str (23) = Val (“50” + “60”) = Val (“5060”) = 5060 Val (“50”) + Val(“60”) = 50+60=110 Val(“Hi”) = 0 Val(“89Hello”) = 89 Val(“89Hi10”) = 89 Str("10") + Str("50") = Str(“Hello”) error
10 50
space
23
Chapter 3 - Visual Basic Schneider
Declaring Variable Types
Use the Dim statement to declare the type of a variable.
Examples: Dim number As Integer Dim flower As String
Dim interestRate As Single
Chapter 3 - Visual Basic Schneider
Data Types
Single: a numeric variable that stores real numbers (0 By default)
Integer: a numeric variable that stores integer numbers (from -32768 to 32767) (0 By default)
String: a variable that stores a sequence of characters (“”empty string By default)
Boolean: a variable that stores True or False (False By default)
Chapter 3 - Visual Basic Schneider
Using Text Boxes for Input/Output
The contents of a text box are always a string type.
Numbers can be stored in text boxes as strings.
Chapter 3 - Visual Basic Schneider
Using Text Boxes for Input/Output
The contents of a text box should be converted to a number before being assigned to a numeric variable.
Val(txtBox.Text) gives the value of a numeric string as a number
Example: Dim numVar as Single numVar = Val(txtBox.Text)
The contents of a text box is always a string
Numbers types into the text box are stored as strings. Therefore, they should be converted to numbers before being assigned to numeric.
Chapter 3 - Visual Basic Schneider
Example
Example 1xString=“528”xValue=Val(xString)
xValue=528Example 2yValue=428yString=Str(yValue)
yString=“428”
“528”
528
xString
xValue
428
“428”
xValue
xString
Chapter 3 - Visual Basic Schneider
Program Documentation
An apostrophe (') is used to indicate that the remainder of the line is a comment. (Comments are ignored by Visual Basic.)
Remarks can appear on a separate line or following a Visual Basic statement.