visualbasicprograming

© 2002 Prentice Hall. All rights reserved.
1
Outline
3.1 Introduction
3.2 Simple Program: Printing a Line of Text
3.3 Another Simple Program: Adding Integers
3.4 Memory Concepts
3.5 Arithmetic
3.6 Decision Making: Equality and Relational Operators
3.7 Using a Dialog to Display a Message
Chapter 3 – Introduction to Visual Basic
Programming

2
3.1 Introduction
• In this chapter we introduce
– Visual Basic programming
• We present examples that illustrate several important features
of the language
– Console applications
• Applications that contain only text output
• Output is displayed in a command window

3
• Simple program that displays a line of text
• When the program is run
– output appears in a command window
• It illustrates important Visual Basic features
– Comments
– Modules
– Sub procedures

© 2002 Prentice Hall.
All rights reserved.
Outline
4
Welcome1.vb
Program Output
1 ' Fig. 3.1: Welcome1.vb
2 ' Simple Visual Basic program.
3
4 Module modFirstWelcome
5
6 Sub Main()
7 Console.WriteLine("Welcome to Visual Basic!")
8 End Sub ' Main
9
10 End Module ' modFirstWelcome
Welcome to Visual Basic!
Single-quote character (')
indicates that the remainder
of the line is a comment
Visual Basic console
applications consist of pieces
called modules
The Main procedure is the entry
point of the program. It is present
in all console applications
The Console.WriteLine
statement displays text output
to the console
•A few Good Programming Practices
– Comments
• Every program should begin with one or more comments
– Modules
• Begin each module with mod to make modules easier to identify
– Procedures
• Indent the entire body of each procedure definition one “level” of
indentation

5
• Now a short step-by-step explanation of how to
create and run this program using the features of
Visual Studio .NET IDE…

6
1. Create the console application
– Select File > New > Project…
– In the left pane, select Visual Basic Projects
– In the right pane, select Console Application
– Name the project Welcome1
– Specify the desired location
2. Change the name of the program file
– Click Module1.vb in the Solution Explorer window
– In the Properties window, change the File Name
property to Welcome1.vb

7
Fig. 3.2 Creating a Console Application with the New Project dialog.
Left pane Right pane
Project
name
File
location

8
Fig. 3.3 IDE with an open console application.
Editor window (containing
program code)

9
Fig. 3.4 Renaming the program file in the Properties window.
Solution Explorer
File Name
property
Click Module1.vb to
display its properties
Properties window

10
3. Change the name of the module
– Module names must be modified in the editor window
– Replace the identifier Module1 with
modFirstWelcome
4. Writing code
– Type the code contained in line 7 of Fig. 3.1 between Sub
Main() and End Sub
• Note that after typing the class name and the dot operator the
IntelliSense is displayed. It lists a class’s members.
• Note that when typing the text between the parenthesis
(parameter), the Parameter Info and Parameter List windows
are displayed

11
5. Run the program
– To compile, select Build > Build Solution
• This creates a new file, named Welcome1.exe
– To run, select Debug > Start Without Debugging

12
Fig. 3.5 IntelliSense feature of the Visual Studio .NET IDE.
Partially-typed member Member list
Description of
highlighted member

13
Fig. 3.6 Parameter Info and Parameter List windows.
Up arrow Down arrow
Parameter List window
Parameter Info window

14
Fig. 3.7 Executing the program shown in Fig. 3.1.
Command window prompts the user to
press a key after the program terminates

15
Fig. 3.8 IDE indicating a syntax error.
Omitted parenthesis character
(syntax error)
Blue underline
indicates a
syntax error
Task List window
Error description(s)

Outline
16
Welcome2.vb
Program Output
1 ' Fig. 3.9: Welcome2.vb
2 ' Writing line of text with multiple statements.
3
4 Module modSecondWelcome
5
6 Sub Main()
7 Console.Write("Welcome to ")
8 Console.WriteLine("Visual Basic!")
9 End Sub ' Main
11
12 End Module ' modSecondWelcome
Welcome to Visual Basic!
Method Write does not position the output
cursor at the beginning of the next line
Method WriteLine positions the output
cursor at the beginning of the next line

17
3.3 Another Simple Program: Adding
Integers
• User input two integers
– Whole numbers
• Program computes the sum
• Display result

Outline
18
Addition.vb
1 ' Fig. 3.10: Addition.vb
2 ' Addition program.
3
4 Module modAddition
5
6 Sub Main()
7
8 ' variables for storing user input
9 Dim firstNumber, secondNumber As String
10
11 ' variables used in addition calculation
12 Dim number1, number2, sumOfNumbers As Integer
13
14 ' read first number from user
15 Console.Write("Please enter the first integer: ")
16 firstNumber = Console.ReadLine()
17
18 ' read second number from user
19 Console.Write("Please enter the second integer: ")
20 secondNumber = Console.ReadLine()
21
22 ' convert input values to Integers
23 number1 = firstNumber
24 number2 = secondNumber
25
26 sumOfNumbers = number1 + number2 ' add numbers
27
28 ' display results
29 Console.WriteLine("The sum is {0}", sumOfNumbers)
30
31 End Sub ' Main
32
33 End Module ' modAddition
Declarations begin with keyword Dim
These variables store strings of characters
These variables store integers values
First value entered by user is assigned
to variable firstNumber
Method ReadLine causes program
to pause and wait for user input
Implicit conversion from String to
Integer
Sums integers and assigns result to
variable sumOfNumbers
Format indicates that the argument
after the string will be evaluated and
incorporated into the string

Outline
19
Addition.vb
Please enter the first integer: 45
Please enter the second integer: 72
The sum is 117

20
3.3 Another Simple Program: Adding
Integers
Fig. 3.11 Dialog displaying a run-time error.
If the user types a non-integer value, such
as “hello,” a run-time error occurs

21
3.4 Memory Concepts
• Variables
– correspond to actual locations in the computer’s memory
– Every variable has a
• Name
• Type
• Size
• value
– A value placed in a memory location replaces the value
previously stored
• The previous value is destroyed
– When value is read from a memory location, it is not
destroyed

22
3.4 Memory Concepts
Fig. 3.12 Memory location showing name and value of variable number1.
Fig. 3.13 Memory locations after values for variables number1 and number2 have been input.
45number1
45
45
number1
number2

23
3.5 Arithmetic
• Arithmetic operators
– Visual Basic use various special symbols not used in algebra
• Asterisk (*), keyword Mod
– Binary operators
• Operates using two operands
– sum + value
– Unary operators
• Operators that take only one operand
– +9, -19

24
3.5 Arithmetic
Fig. 3.14 Memory locations after an addition operation.
45
45
number1
number2
sumOfNumbers 45

25
3.5 Arithmetic
• Integer division
– Uses the backslash,
– 7 4 evaluates to 1
• Floating-point division
– Uses the forward slash, /
– 7 / 4 evaluates to 1.75
• Modulus operator, Mod
– Yields the remainder after Integer division
– 7 Mod 4 yields 3

26
3.5 Arithmetic
Visual Basic operation Arithmetic operator Algebraic expression Visual Basic
expression
Addition + f + 7 f + 7
Subtraction – p – c p - c
Multiplication * bm b * m
Division (float) / x / y or <Anchor10> or
x y
x / y
Division (Integer) none v u
Modulus % r mod s r Mod s
Exponentiation ^ q p q
^ p
Unary Negative - –e –e
Unary Positive + +g +g
Fig. 3.14 Arithmetic operators.
Fig. 3.14 Arithmetic Operators.

27
3.5 Arithmetic
• Rules of operator precedence
1. Operators in expressions contained within parentheses
2. Exponentiation
3. Unary positive and negative
4. Multiplication and floating-point division
5. Integer division
6. Modulus operations
7. Addition and subtraction operations

28
3.5 Arithmetic
Operator(s) Operation Order of evaluation (precedence)
( ) Parentheses Evaluated first. If the parentheses are nested, the
expression in the innermost pair is evaluated first. If
there are several pairs of parentheses “on the same
level” (i.e., not nested), they are evaluated from left
to right.
^ Exponentiation Evaluated second. If there are several such operators,
they are evaluated from left to right.
+, – Sign operations Evaluated third. If there are several such operators,
*, / Multiplication and
Division
Evaluated fourth. If there are several such operators,
Integer
division
Evaluated fifth. If there are several such operators,
Mod Modulus Evaluated sixth. If there are several such operators,
+, – Addition and
Subtraction
Evaluated last. If there are several such operators,
Fig. 3.15 Precedence of arithmetic operators.
Fig. 3.15 Precedence of arithmetic operators.

29
3.5 Arithmetic
Fig. 3.16 Order in which a second-degree polynomial is evaluated.
Step 1.
Step 2.
Step 5.
Step 3.
Step 4.
Step 6.
y = 2 * 5 * 5 + 3 * 5 + 7
2 * 5 is 10 (Leftmost multiplication)
y = 10 * 5 + 3 * 5 + 7
10 * 5 is 50 (Leftmost multiplication)
y = 50 + 3 * 5 + 7
3 * 5 is 15 (Multiplication before addition)
y = 50 + 15 + 7
50 + 15 is 65 (Leftmost addition)
y = 65 + 7
65 + 7 is 72 (Last addition)
y = 72 (Last operation—place 72 into y)

30
3.6 Decision Making: Equality and
Relational Operators
• If/Then structure
– Allows a program to make decision based on the truth or
falsity of some expression
– Condition
• The expression in an If/Then structure
– If the condition is true, the statement in the body of the
structure executes
– Conditions can be formed by using
• Equality operators
• Relational operators

31
Standard algebraic
equality operator or
relational operator
Visual Basic
equality
or relational
operator
Example
of Visual Basic
condition
Meaning of
Visual Basic condition
Equality
operators
= = x = y x is equal to y
<> x <> y x is not equal to y
Relational
operators
> > x > y x is greater than y
< < x < y x is less than y
>= x >= y x is greater than or equal to y
? <= x <= y x is less than or equal to y
Fig. 3.17 Equality and relational operators.
Fig. 3.17 Equality and relational operators.

Outline
32
Comparison.vb
1 ' Fig. 3.19: Comparison.vb
2 ' Using equality and relational operators.
3
4 Module modComparison
5
6 Sub Main()
7
8 ' declare Integer variables for user input
9 Dim number1, number2 As Integer
10
11 ' read first number from user
12 Console.Write("Please enter first integer: ")
13 number1 = Console.ReadLine()
14
15 ' read second number from user
16 Console.Write("Please enter second integer: ")
17 number2 = Console.ReadLine()
18
19 If (number1 = number2) Then
20 Console.WriteLine("{0} = {1}", number1, number2)
21 End If
22
23 If (number1 <> number2) Then
24 Console.WriteLine("{0} <> {1}", number1, number2)
25 End If
26
27 If (number1 < number2) Then
28 Console.WriteLine("{0} < {1}", number1, number2)
29 End If
30
31 If (number1 > number2) Then
32 Console.WriteLine("{0} > {1}", number1, number2)
33 End If
Variables of the same type may
be declared in one declaration
The If/Then structure compares the values
of number1 and number2 for equality

Outline
33
Comparison.vb
Program Output
34
35 If (number1 <= number2) Then
36 Console.WriteLine("{0} <= {1}", number1, number2)
37 End If
38
39 If (number1 >= number2) Then
40 Console.WriteLine("{0} >= {1}", number1, number2)
41 End If
42
43 End Sub ' Main
44
45 End Module ' modComparison
Please enter first integer: 1000
Please enter second integer: 2000
1000 <> 2000
1000 < 2000
1000 <= 2000
515 <> 49
515 > 49
515 >= 49
333 = 333
333 <= 333
333 >= 333

34
Operators Associativity Type
() left to right parentheses
^ left to right exponentiation
* / left to right multiplicative
left to right integer division
Mod left to right modulus
+ - left to right additive
= <> < <= > >= left to right equality and relational
Fig. 3.19 Precedence and associativity of operators introduced in this chapter.
Fig. 3.19 Precedence and associativity of operators introduced in this chapter.

35
• Dialogs
– Windows that typically display messages to the user
– Visual Basic provides class MessageBox for creating
dialogs

Outline
36
SquareRoot.vb
Program Output
1 ' Fig. 3.20: SquareRoot.vb
2 ' Displaying square root of 2 in dialog.
3
4 Imports System.Windows.Forms ' Namespace containing MessageBox
5
6 Module modSquareRoot
7
8 Sub Main()
9
10 ' Calculate square root of 2
11 Dim root As Double = Math.Sqrt(2)
12
13 ' Display results in dialog
14 MessageBox.Show("The square root of 2 is " & root, _
15 "The Square Root of 2")
16 End Sub ' Main
17
18 End Module ' modThirdWelcome
Sqrt method of the Math class is called
to compute the square root of 2
The Double data type stores floating-
point numbers
Method Show of class MessageBox
Line-continuation character
Empty command
window

37
Fig. 3.21 Dialog displayed by calling MessageBox.Show.
Title bar
Close box
Mouse pointer
Dialog sized to
accommodate
contents.
OK button allows
the user to dismiss
the dialog.

38
• Assembly
– File that contain many classes provided by Visual Basic
– These files have a .dll (or dynamic link library) extension.
– Example
• Class MessageBox is located in assembly
System.Windows.Forms.dll
• MSDN Documentation
– Information about the assembly that we need can be found in
the MSDN documentation
– Select Help > Index… to display the Index dialog

39
Fig. 3.22 Obtaining documentation for a class by using the Index dialog.
Search string
Filter
Link to MessageBox
documentation

40
Fig. 3.23 Documentation for the MessageBox class.
Requirements
section heading
MessageBox class
documentation
Assembly containing
class MessageBox

41
• Reference
– It is necessary to add a reference to the assembly if you wish
to use its classes
– Example
• To use class MessageBox it is necessary to add a reference
to System.Windows.Forms
• Imports
– Forgetting to add an Imports statement for a referenced
assembly is a syntax error

42
Fig. 3.24 Adding a reference to an assembly in the Visual Studio .NET IDE.
References
folder
(expanded)
Solution Explorer
before reference is
added
Solution Explorer
after reference is
added
System.Windows.Forms
reference

43
Fig. 3.25 Internet Explorer window with GUI components.
Label
Button (displaying
an icon) Menu (e.g., Help) Text box Menu bar

visualbasicprograming

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