Web-Enabled Decision Support Systems
Visual Basic .NET Programming Language
Prof. Name
Position
University Name
name@email.com
(123) 456-7890
1
Overview

11.1 Introduction

11.2 Visual Basic Statements

11.3 InputBox and MessageBox

11.4 Visual Basic Data Types

11.5 Adding Windows Forms and Setting Start-up Form

11.6 Control Structures

11.7 Arithmetic, Logical, and String Operators

11.8 Arrays

11.9 Multi-Dimensional Arrays

11.10 Dynamic Arrays

11.11 Code Debugging

11.12 In-Class Assignment

11.13 Summary
2
Introduction

A computer program is a sequence of precise, unambiguous, and
detailed instructions on how to complete a task, written in a language
that can be interpreted by a computer
– A programming language is language used to express these instructions

Visual Basic is an example of one such programming language
– Visual Basic statements are similar to sentences in English
 Have specific syntax, nouns, verbs, etc.
 Grouped into subroutines, functions, and modules to enhance the readability
and flow of logic of an application
3
Overview

11.1 Introduction

11.2 Visual Basic Statements

11.3 InputBox and MessageBox

11.4 Visual Basic Data Types

11.5 Adding Windows Forms and Setting Start-up Form

11.6 Control Structures

11.7 Arithmetic, Logical, and String Operators

11.8 Arrays

11.9 Multi-Dimensional Arrays

11.10 Dynamic Arrays

11.11 Code Debugging

11.12 In-Class Assignment

11.13 Summary
4
Visual Basic Statements

A Visual Basic statement is a complete instruction written in the VB
language
– Language syntax are the rules and regulations that govern the composition
of VB statements
– Each statement contains one or more of the following elements:
 Keywords: Reserved words of the language
 Variables: Containers for values
 Constants: Special variables with fixed values
 Operators: Symbols used to perform arithmetic and logical operations
 Operands: Numerical or string values that may be parts of expressions
 Expressions: Combinations of one or more of the above terms that yields a value
5
Keywords

Keywords are the reserved words of a programming language
– Convey the same specific meaning every time they are used
Visual Basic Code Example
Boolean
ByRef
ByVal
Case
Class
Const
Date
Dim
Do
Double
Else
ElseIf
EOF
End
Exit
False
For
Function
If
InputBox
Visual Basic Keywords
6
Loop
Case
Mod
Month
Null
ReDim
True
With
Variables

A variable is a temporary name given to a memory location
– When writing a program, we need to store, manipulate, and reuse
intermediate data values
– Variables can temporarily store values and thus act like containers

We use the keyword Dim to declare variables in Visual Basic
– Allocates or reserves the space for values to be stored
– Variable declaration syntax:
Dim <Variable Name> As <Data Type> [= <Initial Values (s) >]
– Examples:
Dim TemperatureF As Integer = 1
Dim Weather As String = “Cold”
Dim Comments As String
7
Constants

A constant is a special type of variable whose value is not allowed to
change once it has been assigned
– We use the keyword Const to declare constants in Visual Basic
– Constant declaration syntax:
Const <Constant Name> As <Data Type> = <Final Values>
– Examples:
Const factor As Integer = 32
Const PI As Integer = 3.14

Visual Basic features two kinds of statements:
– Declaration statements name and create variables, determine their types,
and assign initial values
– Executable statements perform an action that generates an output and can
be stored in declared variables
8
Overview

11.1 Introduction

11.2 Visual Basic Statements

11.3 InputBox and MessageBox

11.4 Visual Basic Data Types

11.5 Adding Windows Forms and Setting Start-up Form

11.6 Control Structures

11.7 Arithmetic, Logical, and String Operators

11.8 Arrays

11.9 Multi-Dimensional Arrays

11.10 Dynamic Arrays

11.11 Code Debugging

11.12 In-Class Assignment

11.13 Summary
9
InputBox and MessageBox

The InputBox function prompts an input dialog box and waits for the
user input
– When the user clicks the OK button on the input dialog box, the function
returns the input value
– Syntax:
Variable x = InputBox (Prompt, Title, Default Response, X-Pos, Y-Pos)

The MessageBox function is used to display a message to the user in
an output dialog box
– Syntax:
MessageBox.Show (Message, Title, Type, Icon)
10
Hands-On Tutorial: User Input/Output

How-to: Use Visual Basic InputBox and MessageBox Functions
1. Create a new Visual Basic project named VisualBasicIntro.
2. Add a new Button control to the default form. Set the Text property of the
button to “Temperature Conversion” and name it, cmdConvert. Use the
GroupBox control with no text value around the Button control.
User Input/Output: Design Window
11
Adding Code Using the Code Window
3. Double-click the Button control to open the Code Window with the
cmdConvert _Click subroutine.
4. Declare the variables TemperatureC and TemperatureF as Integers, and
write conversion logic as shown below.
User Input/Output: Code Window
12
Saving and Running the Application
5. Save and run the application to view the output shown below.
User Input/Output: Application Output
13
The InputBox Function

InputBox syntax:
Variable x = InputBox (Prompt, Title, Default Response, X-Pos, Y-Pos)
– Elements:
 Prompt: A string that appears as a text inside the dialog box that prompts the user
 Title: A string that appears in the title bar of the dialog box
 Default: The default value of the InputBox, displayed when the dialog box is shown
to the user
 X-Pos, Y-Pos: Integer values for X and Y co-ordinates for positioning the dialog
box on the screen

Examples:
InputBox (“Enter Your Age”, “Age Calculator”, , 100,100) – No default value
InputBox (“Enter Your Age”, ,25) – No Title and No X-Pos and Y-Pos
InputBox (“Only Prompt”)
14
The MessageBox Function

MessageBox syntax:
MessageBox.Show (Message, Title, Type, Icon)
– Elements:
 Message: The text to display (may may be a string, integer, variable, or some
combination of these)
 Title: A string that appears as a text in the title bar of the dialog box
 Type: The type of MessageBox
 Icon: Icon for the MessageBox

Examples:
MessageBox.Show(“Your Age is :=”
& Age, “Age Calculator”, _
MessageBoxButtons.OK, MessageBoxIcon.Information)
MessageBox.Show(“Your Age is :=”
& Age, “Age Calculator”)
MessageBox.Show(“Your Age is :=”
& Age)
15
MessageBox Options
Option
Description
MessageBoxButtons.AbortRetryIgnore
Allows user to abort, retry, or ignore the running operation.
MessageBoxButtons.OKCancel
Allows user to either continue or cancel the operation.
MessageBoxButtons.YesNoCancel
Allows user to respond in yes or no format or select cancel to
exit.
Shows an exclamation mark on the dialog box. Used to
MessageBoxIcon.Warning
indicate caution.
MessageBoxIcon.Information
Shows an information mark on the dialog box.
MessageBoxIcon.Error
Shows an error mark on the dialog box.
MessageBoxIcon.Question
Shows a question mark on the dialog box.
MessageBox Buttons and Icons
16
Visual Basic’s Online Help

The Visual Studio IDE assists us in the process of application
development, making it an interactive process
– Tool Tips provide help on the syntax of statements
Example of Online Tool Tip
– IntelliSense intelligently displays only the relevant methods or options
The MessageBox IntelliSense
17
Adding Comments to Visual Basic Code

Comments are text lines that begin with a single quote or apostrophe (‘)
character
– Used to write useful explanatory comments along with the code lines
– Ignored while the program is executing
– Examples:
'This entire line is a now a VB comment.
Dim TemperatureF As Integer
'Variable Holds the Temp in F
18
Overview

11.1 Introduction

11.2 Visual Basic Statements

11.3 InputBox and MessageBox

11.4 Visual Basic Data Types

11.5 Adding Windows Forms and Setting Start-up Form

11.6 Control Structures

11.7 Arithmetic, Logical, and String Operators

11.8 Arrays

11.9 Multi-Dimensional Arrays

11.10 Dynamic Arrays

11.11 Code Debugging

11.12 In-Class Assignment

11.13 Summary
19
Visual Basic Data Types

When we declare a new variable, we must specify its data type
– Indicates the kind of data that will be stored in the variable
Data Type
Size
Range
Integer
4 Bytes
- 2,147,483,648 to 2,147,483,648
Long
8 Bytes
~ - 9.2 x 10
Double
8 Bytes
~ - 1.79 x 10
String
Variable
0 to 2 Billion Characters
Char
2 Bytes
0 to 65535
Boolean
2 Bytes
True or False
Date
8 Bytes
January 1, 0001 to December 31, 9999
Object
4 Bytes
Anything that can be stored as a Object
18
18
to 9.2 x 10
308
to 1.79 x 10
308
Visual Basic Data Types
20
Checking and Converting Data Types

Two common operations are associated with data types:
– Checking existing data types
– Converting to other data types

Visual Basic provides excellent support for data type manipulations with
its dozens of built-in functions

Checking functions are also known as logical functions, as they check
for a particular data type and return a logical True or False value
– Examples:
IsNumeric ()
Returns True if numeric value; False otherwise.
IsDate ()
Returns True if date value; False otherwise.
IsArray ()
Returns True if an Array; False otherwise.
IsError ()
Returns True if an Error; False otherwise.
21
Conversion Functions


Examples:
CInt
Converts to the Integer data type.
CLng
Converts to the Long data type.
CDbl
Converts to the Double data type.
CStr
Converts to the String data type.
CBool
Converts to the Boolean data type.
CDate
Converts to the Date data type.
CObj
Converts to the Object data type.
There is a generic function, CType, for data type conversions:
– Syntax:
CType (ConvertMe, toThis)
22
Hands-On Tutorial: Data Type Conversion

How-to: Use Data Type Conversion Functions
1. Continue with the VisualBasicIntro project and Form1 from the “Temperature
Conversion” hands-on tutorial. Add a cmdDataTypeConvert command
button, and change the Text property to “Data Type Conversion”. Use the
GroupBox control with no text value around the Button control.
Data Type Conversion Example: Design Window
23
Adding Code
2. Associate the code below with the newly added command button.
Data Type Conversion Example: Code Window
24
Running the Application
3. Press Ctrl+F5 to run and test the application.
Data Type Conversion Example: Application Output
25
Hands-On Tutorial: Data Type Checking

How-to: Use Data Type Checking Functions
1. Continue with Form1 from the previous hands-on tutorial. This time add a
cmdDataTypeChk command button; change its Text property to “Data Type
Checking”.
Data Type Checking Example: Design View
26
Adding Code and Running
2. Associate the code below with the cmdDataTypeChk_Click event.
Data Type Checking Example: Code Window
3. Save and run the application.
Data Type Checking Example: Output Window
27
Overview

11.1 Introduction

11.2 Visual Basic Statements

11.3 InputBox and MessageBox

11.4 Visual Basic Data Types

11.5 Adding Windows Forms and Setting Start-up Form

11.6 Control Structures

11.7 Arithmetic, Logical, and String Operators

11.8 Arrays

11.9 Multi-Dimensional Arrays

11.10 Dynamic Arrays

11.11 Code Debugging

11.12 In-Class Assignment

11.13 Summary
28
Adding Windows Forms

How-to: Add a Windows Form to the Existing Project
1. Choose Project | Add Windows Form from the Main menu to open the Add
New Item dialog box.
2. Select Windows Form in the templates area of the window; accept the
default form name and click the Add button.
Adding a New
Windows Form
29
Setting Start-up Form

How-to: Set the Start-up Form
1. Choose Project | <Project Title> Properties from the Main menu to open the
Properties page.
2. Select the desired startup form from the “Startup form” drop down list. Press
Ctrl+S to save the settings.
Setting the Startup Form
30
Overview

11.1 Introduction

11.2 Visual Basic Statements

11.3 InputBox and MessageBox

11.4 Visual Basic Data Types

11.5 Adding Windows Forms and Setting Start-up Form

11.6 Control Structures

11.7 Arithmetic, Logical, and String Operators

11.8 Arrays

11.9 Multi-Dimensional Arrays

11.10 Dynamic Arrays

11.11 Code Debugging

11.12 In-Class Assignment

11.13 Summary
31
Control Structures

Control structures allow us to control the flow of program execution
– By default, a program is executed sequentially:
 Left to right
 Top to bottom
– Control structures allow us to skip over or loop a given section of the code
– Classified into two categories:
 Decision structures: Allow us to test conditions
 Loop structures: Allow us to execute one or more lines of code repetitively
32
If-Then

We use an If-Then structure to execute one or more statements
conditionally
– Syntax:
If (<condition>) Then
Body of If
End If
– Examples:
'Check whether the input number is greater than 100
If (x > 100) Then
MessageBox.Show(”The Input Number is greater than 100”)
End If
'Check whether Num is zero
If (Num = 0) Then
Factorial = 1
End If
33
If-Then-Else

The Else statement allows us to specify the action to be performed if the
condition of the If statement is not satisfied
– Syntax:
If (<condition>) Then
Body of If
Else
Body of Else
End If
– Example:
'Check whether the input is an even or odd number
If (x Mod 2) = 0 Then
MessageBox.Show(x & “is an even number”)
Else
MessageBox.Show(x & “is an odd number”)
End If
34
If-Then-Else – Logical Flow Chart
If-Then-Else Structure’s Logical Flow Chart
35
If-Then-ElseIf-Else

We can use an If-Then-ElseIf-Else statement to apply multi-level
selections
– Syntax:
If (<condition1>) Then
Body of If1
ElseIf (<condition2>) Then
Body of If2
.
.
Else
Body of Else
End If
– Example:
'Compare the input numbers
If (a > b) Then
MessageBox.Show(“The First Number is greater than Second Number”)
ElseIf (b > a) Then
MessageBox.Show(“The Second Number is greater than First Number”)
Else
MessageBox.Show(“Both Input Numbers are Equal”)
End If
36
The RadioButton Control

RadioButton controls force their users to select from a set of two or
more mutually exclusive choices
– Often used properties and events of a RadioButton control:
Name
Description
Checked
Sets/gets a value indicating whether the radio button is checked.
Image
Sets/gets a checkbox image.
CheckedChanged
Occurs when the Checked property changes.
– Example:
RadioButton
Control Example
37
Hands-On Tutorial: Using If-Then-Else Structure

How-to: Use the If-Then-Else Control Structure and RadioButton Control
1. Design Form2 as shown below. Make Form2 the start-up form. Name the
three RadioButton controls as: radBS, radMS and radPhD, and name the
Button control as cmdCheckStatus.
RadioButton Control Example: Degree Selection
38
Adding Code and Running
2. Associate the code below with the command button’s Click event.
Code Window
3. Save, run, and test the application.
Application
Output
39
Using Select-Case Structures

The Select-Case structure selectively executes one among multiple
“cases”
– A single test expression is evaluated once and compared with the values of
each case clause in the structure
 Only the first matching case gets executed
– Conceptually similar to the If-Then-Else structure
 Enhances code readability when there are several possibilities to consider
– Syntax:
Select Case <TestExpression>
Case <Expression 1>
Body of Case1
Case <Expression 2>
Body of Case2
.
.
Case <Expression n>
Body of Case n
Case Else
Body of Case Else
End Select
40
Select-Case Structure - Flowchart
Select-Case Structure’s
Logical Flow Chart
41
Select-Case Structure - Example

Numbers a and b and operator op (+, -, *, /) are user inputs
– Depending upon the input operator, we can perform the correct operation
using a case statement as follows:
Select Case op
Case +
MessageBox.Show(“a + b
Case MessageBox.Show(“a - b
Case *
MessageBox.Show(“a * b
Case /
MessageBox.Show(“a / b
Case Else
MessageBox.Show(“Enter
End Select
42
=”
& (a + b))
=”
& (a - b))
=”
& (a * b))
=”
& (a / b))
only (+ OR - OR * OR /) Operators”)
The TextBox Control

A TextBox control is a box-shaped control that can display text data or
allow the user to input the text data
– Can have multiple lines and scroll bars
– Can be made read-only
– Most important property is Text, which allows us to access the text value
Example of a TextBox Control
43
Hands-On Tutorial:
Working with Select-Case Structure

How-to: Use the Select-Case Control Structure and TextBox Control
1. Add a new form, Form3, to the VisualBasicIntro project and set Form3 as the
start-up form. Add a TextBox named txtMonthAbbr and a command button,
cmdCheckDays.
2. Design the form as shown below.
Select-Case Structure Example: Design View
44
Adding Code and Running
3. Use the code shown below for the Click event of the command button. Save,
run, and test the application.
Select-Case Structure Example: Code Window
45
Loop Structures

Loop structures are used to execute blocks of statements multiple times
– Here, we discuss four types:
 Do-Loop-While, Do-While-Loop, Do-Loop-Until, and Do-Until-Loop
– Each variant evaluates a Boolean condition to determine whether or not to
continue the execution of the loop
– Categorize by when the Boolean condition is checked:
 Prior to loop execution: Do-While-Loop and Do-Until-Loop
 After the loop execution: Do-Loop-While and Do-Loop-Until
– Categorize by how the Boolean condition is interpreted:
 Continue loop execution while the condition is true, stop once it is false: Do-WhileLoop and Do-Loop-While
 Continue loop execution until the condition is false, stop once it is true: Do-UntilLoop and Do-Loop-Until
46
Logical Flow Charts
Do-Loop-While and Do-While-Loop: Logical Flow Charts
47
Do-Loop-While

Syntax:
Do
Body of the loop
Loop While (<condition>)

Example:
48
Do-While-Loop

Syntax:
Do While (<condition>)
Body of the loop
Loop

Example:
49
Do-Loop-Until

Syntax:
Do
Body of the loop
Loop Until (<condition>)

Example:
50
Do-Until-Loop

Syntax:
Do Until (<condition>)
Body of the loop
Loop

Example:
51
Hands-On Tutorial:
Working with Do-Loop Structure

How-to: Use the Do-Loop Control Structure
1. Add a new form, Form4, to the existing project. Set Form4 as a startup form.
2. Add three TextBox controls named txtFirstNum, txtSecondNum and
txtSumStep. Also add a Button control named cmdSum.
Sum Using Do-Loop-While Structure: Design Window and Output
52
Adding Code and Running
3. Use the code below for the Click event of the cmdSum Button control.
4. Save, run, and test the application.
53
Alternative Coding

Do-While-Loop:

Do-Until-Loop:

Do-Loop-Until:
54
For-Next Structures

The Do-Loop structures works well when we do not know how many
times we must execute the loop statements

For-Next is an alternative when we know the specific number of times
we want to execute the loop
– Syntax:
For <counter = Start Value> To <End Value> [Step <Increment Value>]
Body of the For Loop
Next
– Example:
55
For-Next Structure – Logical Flow Chart
For-Next Structure’s Logical Flow Chart
56
Hands-On Tutorial:
Working with the For-Next Loop Structure

How-to: Use the For-Next Control Structure
1. Add a new form, Form5, to the existing project. Set the Form5 as a startup
form. Set up this form and form controls as shown below.
For-Next Loop Structure Example: Design View
57
Adding Code and Running
2. Use the code below for the Click event of the command button.
3. Save, run, and test the application.
58
For-Each-Next Loop Structure

The For-Each-Next structure syntax is essentially the same as the ForNext syntax except that the loop is executed for each element of the
group instead of a specific number of times
– Helpful if we need to perform operations on groups such as CheckBoxes
– Syntax:
For Each <element> In <Group>
Body of the For loop
Next
– Example:
59
The Exit Statement

The Exit statement allows us to end the execution of a loop, subroutine,
or function
– Syntax:
Exit <What?>
– Examples:





Exit Sub
Exit Select
Exit Do
Exit For
Exit Function
60
Exit Statement - Example

“Exit Sub” example:
61
Overview

11.1 Introduction

11.2 Visual Basic Statements

11.3 InputBox and MessageBox

11.4 Visual Basic Data Types

11.5 Adding Windows Forms and Setting Start-up Form

11.6 Control Structures

11.7 Arithmetic, Logical, and String Operators

11.8 Arrays

11.9 Multi-Dimensional Arrays

11.10 Dynamic Arrays

11.11 Code Debugging

11.12 In-Class Assignment

11.13 Summary
62
Arithmetic Operators

Arithmetic operators operate on one or more operands to produce an
output value
Operator
Meaning
Example
*, /
Multiplication and division
x * y. Multiply x with y
+, -
Addition and subtraction
x + y. Add x to y
^
Exponential
x ^ y. x to the power of y
Mod
Modulo
x Mod y. x Modulo y
*=, /=
Multiplication/division followed by assignment
x *=y. x = x* y
+=, -=
Addition/subtraction followed by assignment
x +=y. x = x + y
= , <>
Equal to, Not equal to
x <> y. x is not equal to y
>,<
Greater than, less than
x > y. x is greater than y
>=, <=
Greater than or equal to, Less than or equal to
x >= y. x is greater than or equal to y
Arithmetic Operators (in order of precedence)
63
Logical Operators
Operator
Meaning
Example
And
Logical And two
X And Y. If both X and Y are true, return true; otherwise, return
operands
false.
Reverse the logical
Not X. If X is true, then return false and vice versa.
Not
value of a operand
Or
Logical Or two
X Or Y. If either X or Y is true, return true; otherwise, return false.
operands
Xor
Logical Exclusive Or
A Xor B. If A is true OR B is true, return true (Exclusive). If both
two operands
A and B have the same value (true/false), return false.
Logical Operators
64
Math Functions

Some of the functions associated with the Math collection:
– Abs: Returns the absolute value of a specified
– Sin, Tan, Cos: Returns the sine, tangent, and cosine values of the angle
– Min, Max: Returns the smaller and greater of the given two numbers
– Floor: Returns the greatest integer less than or equal to its numeric
argument
– Ceiling: Returns the smallest integer greater than or equal to its numeric
argument
– Sqrt: Returns the square root of the specified number
– Pow: Returns the specified number raised to the specified power
65
Math Functions - Example

We illustrate the use of Pow and Sqrt math functions with an example of
Pythagoras' Theorem:
– Calculate the length of the hypotenuse (output) of a right-angled triangle,
given the length of its other two sides (inputs)
– Code:
Pythagoras’ Theorem Example: Code Window
66
Handling Strings

Working with the String data type is an important aspect of the
application development process
– VB .NET has tremendous support for string manipulation
– We can perform a variety of operations on strings:





Change the string case
Get part of the string
Concatenate two strings
Compare two strings
Search a string
67
String Operations

The following table summarizes the VB .NET String operations:
What to do
How
Concatenate two strings
&, +, String.Concat
Compare two strings
String.CompareTo(CompareMe), String.Equals(CompareMe)
Copy String
=, String.Copy(CopyFrom)
Change Case
UCase, LCase, String.ToUpper
Length
Len, String.Length
Substring
String.Substring(StartPos, Length)
String Search
String.IndexOf(SearchString)
Trim Spaces
LTrim, RTrim, String.Trim
String Operations
68
Hands-On Tutorial: String Operations

How-to: Use String Concat, Compare, Substring, IndexOf, and Length
Functions
1. Add a form, Form6, to the current project and set it as the start-up form.
2. Design the form as shown below.
3. Each of the GroupBox controls illustrates a string operation.
Illustrating String Operators:
The Form in Design Window
69
Adding Code
4. Use the code below to assign code to the appropriate command buttons.
Illustrating String Operators: Code Window1
70
Adding Code (cont.)
4. Use the code below to assign code to the appropriate command buttons.
Illustrating String Operators: Code Window2
71
Save and Run
5. Save, run, and test the application.
Illustrating String Operators: Application Output
72
Overview

11.1 Introduction

11.2 Visual Basic Statements

11.3 InputBox and MessageBox

11.4 Visual Basic Data Types

11.5 Adding Windows Forms and Setting Start-up Form

11.6 Control Structures

11.7 Arithmetic, Logical, and String Operators

11.8 Arrays

11.9 Multi-Dimensional Arrays

11.10 Dynamic Arrays

11.11 Code Debugging

11.12 In-Class Assignment

11.13 Summary
73
Arrays

An array is a basic data structure that allows us to refer to multiple
variables by the same name
– All the variables (or elements) in an array have the same data type
– Array declaration syntax:
Dim <Array Name> As <Data Type> ([<Array Size>-1])
– Examples:
Dim IntArray (4) As Integer
Dim DobArray (14) As Date
Dim LongArray (49) As Long
'5 elements
'15 elements
'50 elements
– Indexing:
Example of an Integer Array
74
Hands-On Tutorial: Working with Arrays

How-to: Declare and Use Arrays
1. Add a new form, Form7, to the existing VisualBasicIntro project. Set Form7
as the start-up form.
2. Design the form as shown below. Name the command button as,
cmdPopulateArray. Set its Text property to “Populate Me”.
An Array Example: Design Window
75
Adding Code
3. For the Click event of the command button cmdPopulateArray, write the
code shown below.
Array Example: Code Window
76
Saving and Running
4. Save, run, and test the application.
Array Example: Application Output
77
The ListBox Control

The ListBox control presents a list of choices to the user
– By default, the choices are displayed vertically in a single column
– Some properties and methods:





SelectedItem: Gets/sets the currently selected item
SelectedIndex: Gets/sets the index of a currently selected item
Items: Gets/sets collection of all the items
Items.Clear: Clears all the items in the list
ClearSelection: Sets SelectedIndex = -1 (clears any selection)
Example of a
ListBox Control
78
Adding Items to a ListBox

We can add items to a list at design-time using the Properties Window
– Locate the Items property in the Property Window
– Click the Build button in the property row to open the String Collection Editor
– The editor allows us to enter item values to the list

We can also add items at run-time in the VB .NET code
– Employ Items.Add method:
Adding Items to a ListBox Control
79
Hands-On Tutorial:
Displaying Array in a ListBox Control

How-to: Add Elements to a ListBox Control
1. Add a new form, Form8, to the existing VisualBasicIntro project. Set Form8
as the start-up form.
2. Add a ListBox and Button controls as shown below. Name the Button control
as cmdArray and the ListBox control as lstArray. Set the Text property of the
ListBox control to “Populate Me”.
Displaying Array in a ListBox Control: Design Window
80
Adding Code and Running
3. Associate the code below with the Click event of the cmdArray command
button.
4. Save and run the application by pressing Ctrl+F5.
81
Overview

11.1 Introduction

11.2 Visual Basic Statements

11.3 InputBox and MessageBox

11.4 Visual Basic Data Types

11.5 Adding Windows Forms and Setting Start-up Form

11.6 Control Structures

11.7 Arithmetic, Logical, and String Operators

11.8 Arrays

11.9 Multi-Dimensional Arrays

11.10 Dynamic Arrays

11.11 Code Debugging

11.12 In-Class Assignment

11.13 Summary
82
Multi-Dimensional Arrays

Multi-dimensional arrays have two or more dimensions
– Visualized as a grid with rows of the grid representing one of the dimensions
and columns representing the other
– Declaration syntax:
Dim <Array Name> ([<1st D Size>]),… ([<nth D Size>]) As <Data Type>
– Example:
Dim Students (3, 4) As Double '4 rows and 5 columns
83
Using Loops with Multi-Dimensional Arrays

We can efficiently process a multi-dimensional array by using nested ForNext loops
– The code below initializes (lines 9-14) and displays (lines 16-21) the Student
array
84
Hands-On Tutorial:
Working with Multi-Dimensional Arrays

How-to: Use Multi-Dimensional Arrays and the DataGridView Control
1. Add a new form, Form9, to the existing VisualBasicIntro project. Set Form9
as the start-up form.
2. Drag and drop a DataGridView control from the Toolbox on Form9. Name the
DataGridView control dgvArray.
3. Add a Button control named cmdMultDArray to the form and set its Text
property to “Enter Grades”.
Displaying a Two-Dimensional
Array in the DataGridView Control:
Design Window
85
Adding Code
4. Associate the code below with the Click event of the command button.
An Example of
Dynamic Arrays:
Code Window
86
Overview

11.1 Introduction

11.2 Visual Basic Statements

11.3 InputBox and MessageBox

11.4 Visual Basic Data Types

11.5 Adding Windows Forms and Setting Start-up Form

11.6 Control Structures

11.7 Arithmetic, Logical, and String Operators

11.8 Arrays

11.9 Multi-Dimensional Arrays

11.10 Dynamic Arrays

11.11 Code Debugging

11.12 In-Class Assignment

11.13 Summary
87
Dynamic Arrays

Dynamic arrays are arrays whose size can be changed at run-time
– As opposed to static arrays which always remain the same size
– Useful when we do not know the exact number of elements to be stored
– Visual Basic lets us assign or change the array size at run time using the
ReDim (re-declare) keyword
– Re-declaration syntax:
ReDim <Array Name> (<Array Size>)
88
Dynamic Array - Example
Dynamic Array Example:
Form Design
Dynamic Array Example:
Code Window
89
Overview

11.1 Introduction

11.2 Visual Basic Statements

11.3 InputBox and MessageBox

11.4 Visual Basic Data Types

11.5 Adding Windows Forms and Setting Start-up Form

11.6 Control Structures

11.7 Arithmetic, Logical, and String Operators

11.8 Arrays

11.9 Multi-Dimensional Arrays

11.10 Dynamic Arrays

11.11 Code Debugging

11.12 In-Class Assignment

11.13 Summary
90
Code Debugging

Debugging is the process of finding and fixing syntax and logical errors

Syntax errors occur because of incorrect syntax use or human errors
– Visual Studio .NET assists us in detecting syntax errors as we write the code
 Underlines the construct where there is a syntax error
Syntax Error in the Outer For-Next Loop Structure
91
Logical Errors

Logical errors arise due to flaws in the logical reasoning of an
application design
– Detecting and handling logical errors can be very challenging
– Often result in run-time exceptions when executed
Logical Error: Run-Time
Error Message for
IndexOutOfRange Exception
92
Using Breakpoints

With breakpoints we can specify a line in the code where we want to
break the execution of a program
– Helps when debugging logical errors
– Program execution pauses at the breakpoint so that we can observe the
values of various variables at that point in time
– To add/remove a breakpoint, click in the selector area of the code line
Adding Breakpoints
to the Code
93
Breakpoint Features

Breakpoints offer many interesting features:
– Break on a breakpoint conditionally
– Skip a breakpoint based on how many times it was hit
Breakpoint Condition
Dialog Box
Breakpoint Hit Count
Dialog Box
94
Using the Watch Window

The Watch Window is used to watch the values of different variables
during the execution of a program
– To open a Watch Window, we must be in debug mode
 We can open a Watch Window by choosing the Debug | Windows | Watch |
Watch1 option form the Main menu
Opening a
Watch Window
95
Using the Watch Window (cont.)

In a Watch Window, we can add the names of the variables we would like
to watch
– The corresponding values are displayed in the Value column
– Every time we break (or pause) the execution using a breakpoint, we can
watch the values of variables
Adding Variables to the Watch Window
96
Using Debug Toolbar and Menu

As we break program execution and watch variables, we have many
options available in the Debug toolbar and Debug menu:
–
–
–
–
–
Continue (F5)
Stop Debugging (Ctrl+Alt+Break)
Step Into (F8)
Step Over (Shift+F8)
Step Out (Ctrl+Shift+F8)
The Debug Menu
97
Debug Menu Options
Option
Description
Continue
Continues the execution until next break point.
Stop Debugging
Stops the execution. Gets us out of debugging mode.
Step Into
Steps into a procedure. If the current line of the program is not a
procedure call, we move to the next line of the code.
Step Over
Executes the procedure without stepping into it. The procedure will be
executed and we move to the next code line. Again, if the current line is
not a procedure call, we move to the next line of the code.
Step Out
Executing remaining statements of the procedure and gets out of the
procedure.
Debug Menu Options
98
Overview

11.1 Introduction

11.2 Visual Basic Statements

11.3 InputBox and MessageBox

11.4 Visual Basic Data Types

11.5 Adding Windows Forms and Setting Start-up Form

11.6 Control Structures

11.7 Arithmetic, Logical, and String Operators

11.8 Arrays

11.9 Multi-Dimensional Arrays

11.10 Dynamic Arrays

11.11 Code Debugging

11.12 In-Class Assignment

11.13 Summary
99
In-Class Assignment

Create a Windows application that will compute the sum of squares of a
series of numbers, given:
– Starting number (SN)
– Ending number (EN)
– Step value (SV)
– Example:
 Given SN=1, EN=5, and SV=1
 The series is 1,2,3,4, and 5
 The sum of squares is 1+2+9+16+25=53
– Directions:
 Use either a Do-While loop or a For-Next loop to compute the sum, and display it
in a MessageBox to the user. Also display a series and square values in two
ListBox controls.
 Use a Double variable to hold the sum of squares. Also, if the value entered for EN
is larger than 100,000, we exit the program without computing the sum.
100
Overview

11.1 Introduction

11.2 Visual Basic Statements

11.3 InputBox and MessageBox

11.4 Visual Basic Data Types

11.5 Adding Windows Forms and Setting Start-up Form

11.6 Control Structures

11.7 Arithmetic, Logical, and String Operators

11.8 Arrays

11.9 Multi-Dimensional Arrays

11.10 Dynamic Arrays

11.11 Code Debugging

11.12 In-Class Assignment

11.13 Summary
101
Summary

A computer program is a sequence of precise, unambiguous, and
detailed instructions on how to complete a task, written in a language that
can be interpreted by a computer.
– A language used to express these instructions is referred as a programming
language.

A complete instruction written in Visual Basic language is known as a
Visual Basic statement.
– The rules and regulations that govern the composition of VB statements are
known as language syntax.
– A Visual Basic statement contains one or more of the following elements:





Keywords: Reserved words for Visual Basic’s use
Variables: Containers for values; temporary names given to memory locations
Constants: Special variables with fixed values
Operators: Symbols used to perform arithmetic and logical operations on operands
Operands: Numerical or string values to operate on
102
Summary (cont.)

We use the keyword Dim to declare a variable in Visual Basic.
– The type of a variable (data type) indicates the kind of data that will be stored
in the variable.



InputBox controls helps us obtain data from a user using a dialog box.
MessageBox controls take a value as an input parameter and display it to
the user in a dialog box.
Control structures allow us to control the flow of program execution; they
consist of two categories, which are based on the behavior they create:
– Decision structures
 Allow us to test conditions (If-Then, Select-Case)
– Loop structures
 Allow us to execute one or more lines of code repetitively (Do-Loops, For-Next
Loops)
103
Summary (cont.)

An array is a basic data structure that allows us to refer to multiple
variables by the same name.
– Visual Basic features two types of arrays:
 A static array whose size always remains the same
 A dynamic array whose size can be changed at run-time

There are two kinds of errors that can occur in a program:
– Syntax errors
 Occur because of incorrect syntax use or human errors
– Logical (semantic) errors
 Arise due to flaws in the logical reasoning of an application design

Debugging is the process of finding and fixing syntax and logical errors
– Detecting and handling logical errors can be very challenging
– Breakpoints and Watch Windows help detect logical errors
104