Visual Basic.NET Comprehensive Concepts and Techniques Chapter 4 Working with Variables, Constants, Data Types, and Expressions

Visual Basic .NETComprehensive Concepts

and Techniques

Chapter 4

Working with Variables, Constants, Data Types,

and Expressions

2Chapter 4: Working with Variables, Constants, Data Types, and Expressions

Objectives

• Use the RadioButton and GroupBox controls

• Set a default button on a form

• Declare variables and constants


Objectives

• Use variables and constants within code

• Describe Visual Basic .NET data types

• Convert between data types

• Code a form Load event procedure

• Use the Option Strict statement


Objectives

• Use arithmetic expressions

• Describe the order of operator precedence in code

• Use the Pmt function

• Use the Format$ function



Starting the Project and Creating the User Interface• Start Visual Basic .NET and click the New

Project button on the Start Page

• Name it Automobile Loan Calculator


Setting Form Properties and Adding Controls


Setting Form Properties and Adding Controls• Add three Label controls, two

NumericUpDown controls, one TextBox control, and two Button controls


Adding a GroupBox Control to a Form• Add the GroupBox control by clicking the

GroupBox button in the Toolbox window and drawing the GroupBox1 control on Form1, as shown below


Adding RadioButton Controls to Create a Group of Controls• Drag the RadioButton button from the

Toolbox window to the top of the GroupBox1 control. Be sure to release the mouse button while the mouse pointer is positioned within the borders of the GroupBox1 control

• Repeat this step to create two more RadioButton controls


Changing Control Properties

• Change the properties of the Label, NumericUpDown, TextBox, and Button controls according to Table 4-4 on page 4.14 and 4.15 in the text


GroupBox Control Properties


RadioButton Control Properties


Setting the Default Button on a Form• Pressing the ENTER key is equivalent to

clicking the button

• Select the AcceptButton property in the properties window for Form1 to btnComputePayment


Declaring Constants and Variables

• A value is a number or string that programmers use in the code

• A variable represents a location in computer memory that can change values as the code executes

• A constant represents a location in computer memory that cannot be changed during execution


Data Types


Declaring Constants and Variables

• Use a value when it shows up only once in the code.

• Use constants to store values that do not change and may be used more than once.

• Use variables to store values that may change as the code executes.


Rules for Naming Constants and Variables

• The name must either :– begin with a letter, or– Begin with an under score followed by at least one valid

character.

• The name cannot contain punctuation or blank spaces.

• The name is not case sensitive (e.g. ScoRe and score are the same variables/constants).

• The name can be up to 16,383 characters in length.


Declaring Variables The general forms:

Dim name as datatype = initial value

Dim name1 as datatype = initial value, name2 as datatype = initial value, ..

Dim name1, name2,… as datatype

Dim name1 as datatype, name2 as datatype, name3 as datatype,…

Dim name1 = initial value, name2 = initial value, name3 = initial value,

Dim name1, name2, name3, …

Dim name1 as datatype = initial value, name2 as datatype, name3 as datatype = initial value,…


e.g. date

Dim Birthday As Date

Birthday = #11/27/1963#

t1.text = Birthday

textbox control


e.g. char

Dim cat As String

cat = “nasa"

Dim ch as char

ch = “a"


e.g. short and boolean

Dim Birds As Short

Birds = 12500

Dim Flag as Boolean

Flag = True


e.g. dim x : MsgBox(x)

x =20: MsgBox(x)

X = “A” : MsgBox(x)

X = true: MsgBox(x)


Dim x, x1 = 20

error


Declaring Constantsconst name as datatype = initial value

const name1 as datatype = initial value, name2 as datatype = initial value, ..

const name1 = initial value, name2 = initial value, name3 = initial value,


Declaring Constants

• Double-click the Form1 form in an area that does not contain a control. When the code window displays, click 189

• Enter the seven lines of code below, and press the ENTER key after entering the last line


Declaring a constant

• The first Form:

Const name As type = value

• The second Form:Const name = value

key words


Declaring a constant

• E.g1:

Const MaxVolume as Integer = 11

• E.g.3: Const capacity = 150.3


Choosing the data Types

• Try to use the data type that takes up the smallest amount of memory.

e.g. if you need to use a variable that takes a value between 0-150 then the best type is Byte. It is waste to use Long for instance.


Choosing the data Types

• Try to use integral data type that represent whole numbers because arithmetic operations are faster with the whole numbers.

• If a variable or constant will not contain a decimal, use nonintegral data type.


Using the option strict statement

• VB.net does not require you to use the same data type on both sides of the assignment.

• VB.net converts the variables or constants to the proper data type on both sides of the assignments.

• This conversion can cause problems and be unreadable for others.



• If you type: Option strict on

– The option strict statement forces VB.net to accept the assignment statement only if it has the same type in both sides.

– The option strict statement forces you to declare a data type for all variables and constant.

– Must be the first line in the code entered in the code window.


e.g.

Option strict on

Public Class Form1

Inherits System.Windows.Forms.Form

' =====================

Const x As Integer = 5

……

……



• If you type: Option strict off

– The option strict statement does not force VB.net to accept the assignment statement only if it has the same type in both sides.

The default


Option strict on

const name = value

dim var

dim var = value

dim var1, var2, var3,…..

Error since there are no types


Declaring variables

• E.g. Option strict on

const capacity = 150.3 Dim score as integer = 0

Dim name as string

Dim address

Error: Option Strict On requires all variable declarations to have an 'As' clause.


Declaring variables/constants

• The scope refers to the places inside the program from which you can access (use) a variable or a constant.

• The scope of a variable or a constant depends on the place of declaring this variable/constant.

• Declaring a variable/constant can either be:

– Local or – Global


Declaring variables/constants

– Local: a variable or a constant is local if it defined within a procedure. It has scope within that procedure only.

– Global : a variable or a constant is global if it is declared in the general area of the code (any place outside the procedures and inside the program)


Converting Data Type

• Convert.toboolean(x) method converts the value of a variable/constant X to a true or false values.

E.g. Dim z As Boolean = True

z = Convert.ToBoolean(-1)

z = Convert.ToBoolean(0)

The result: z = true The result: z

= falseIf 0 then z is false

Any other value z is true

z = CBool(-1)

z = CBool(0)The same



• Convert.tostring(x) method converts the value of a variable/constant X to a string.

E.g. Dim z As string

Dim x As double = 3.245

z = Convert.Tostring(x)

The result Z = ”3.245“

z = CStr(x)The same



• Convert.toint16(x) 0r CShort(x) method converts the value of a variable/constant X to short.

• Convert.toint32(x) or CInt(x) method converts the value of a variable/constant X to integer.

• Convert.toint64(x) or CLng(x) method converts the value of a variable/constant X to long.

• E.g. option strict off ………

Dim z, y, k As Integer z = Convert.ToInt16(34.24) y = Convert.ToInt32(34.54) k = Convert.ToInt64(34.94)

The result z = 34

The result y = 35The result k = 35

If the resulting value is greater than the maximum value that the short can save then the program will hang



• E.g. option strict on Dim z, y, k As Integer

z = Convert.ToInt16(34.24)

y = Convert.ToInt32(34.54)

k = Convert.ToInt64(34.94)The result z = 34

The result y = 35Error :cannot convert from long to int


Option Strict OnPublic Class Form1 Private Sub Button1_Click(ByVal sender As

System.Object, ByVal e As System.EventArgs) Handles Button1.Click

T1.Text = 3 + 2 MsgBox(T1.Text) End SubEnd Class

Error 1 Option Strict On disallows implicit conversions from 'Integer' to 'String'.


Option Strict OffPublic Class Form1 Private Sub Button1_Click(ByVal sender As


T1.Text = 3 + 2 MsgBox(T1.Text) End SubEnd Class




Dim x As Integer x = 5 * 3 + 4 + 2 MsgBox(x) End SubEnd Class




Dim x As Integer x = 5 * 3 + 4 + 2.0 MsgBox(x) End SubEnd Class

Error 1 Option Strict On disallows implicit conversions from 'Double' to 'Integer'.


Converting Data TypeOption Strict OffPublic Class Form1

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

Dim z, y, k As Integer z = Convert.ToInt16(34.24) y = Convert.ToInt32(34.54) k = Convert.ToInt64(4123456789012)

End SubEnd Class

Error: Arithmetic operation resulted in an overflow.


Converting Data TypePublic Class Form1

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

Dim z As Integer

z = Convert.ToInt16(4123456789012)

End Sub

End Class

Error: value was either too large or too small for an Int16.



• Convert.todouble(x) or CDbl(x) method converts the value of a variable/constant X to a double.

Dim z As double

z = Convert.Todouble(34)

The result Z = 34.0


option strict off

Dim x As Integer = 300

Dim y As Byte

y = x

Error: overflow


option strict off


Dim y As Byte

y = x

No error


Option strict off

Dim x As Integer

x = "23“

No error


Option strict off

Dim x As Integer

x = "23st“

error


Option strict off

Dim x As Intege

x = “A“

error


option strict on


Dim y As Byte

y = x

Error 1 Option Strict On disallows implicit conversions from 'Integer' to 'Byte'.


option strict on


Dim y As Byte

y = x

Error 1 Option Strict On disallows implicit conversions from 'Integer' to 'Byte'.


option strict on


Dim y As Byte

x = y

No error


Option strict on

Dim x As Integer

x = "23“

Error 1 Option Strict On disallows implicit conversions from 'String' to 'Integer'.


Option strict on

Dim x As Integer

x = "23st“

Error 1 Option Strict On disallows implicit conversions from 'String' to 'Integer'.


Option strict on

Dim x As Integer

x = “A“

Error Option Strict On disallows implicit conversions from 'String' to 'Integer'.


Option strict off

Dim x As Integer

x = 3 + "6" + 2

MsgBox(x)

The result is x = 11


Option strict on

Dim x As Integer

x = 3 + "6" + 2

MsgBox(x)

errorOption Strict On disallows implicit conversions from 'String' to 'Double'.


Option Strict OffDim x As Integerx = 3 + "6kk" + 2MsgBox(x)

errorConversion from string "6kk" to type 'Double'

is not valid.


Option Strict Off

Dim x As String

x = 3 + "6" + 2

MsgBox(x)

The result is x = 11


Option Strict OnPublic Class Form1

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

Dim x As String x = 3 + "6" + 2 MsgBox(x)

End SubEnd Class

Error 1 Option Strict On disallows implicit conversions from 'String' to 'Double'.


Option strict off

Dim x As Integer

x = 3.5

MsgBox(x)

The result is x = 4


Exercise: try the following

Option Strict Off

Option Strict On

Dim x As Integer

x = 3.5

MsgBox(x)


Option strict on

Dim x As Integer

x = 3.5

MsgBox(x)



Option Strict On

Dim x As Integer

x = 4 Mod 3

MsgBox(x)

The result is x =1


Option Strict On

Dim x As Integer

x = 2 + 5 * 2.0

MsgBox(x)



Numeric Expressions and Operator Precedence

• An expression can perform a calculation, manipulate characters , call a function or test data.

• A numeric expression is any expression that can be evaluated as a number.



• A numeric expression can include values, variables, constants, control properties and arithmetic operators (^, *, /,\,mod,+,-).

• A numeric expression cannot contain string variables, string constants or objects.


Arithmetic operator

• ^ (e.g. the result of 2^3 is 8)• * (e.g. the result of 2*3 is 6)• / used to divide two numbers and

return a decimal result. (e.g. the result of 3/2 is 1.5).• \ used to divide two numbers and

return an integer result. (e.g. the result of 3/2 is 1):

– The backslash operator (\) first round the dividend and the divisor to integers, then

– it truncates any decimal portion of the quotient.

– E.g. 5\2 is equal to 2, 8.9 \ 2.4 is equal to 4


Arithmetic operator

• Mod (e.g. the result of 5 mod 2 is 1).• + (e.g. the result of 3 + 2 is 5).• - (e.g. the result of 3 - 2 is 1).


Numeric Expressions. E.g.

• The following expressions are invalid: A = 2b

C = 6 + “debit” /c

D = “25” /b +”x” -19

It should be 2 * b


The precedence in the numeric expression

• A numeric expression is evaluated from left to right according to the following precedence as follows:– Parenthesis: ()– Exponentiation: ^– Multiplication: *, division: /– integer division: \– Mod operator: mod– Addition: + and subtraction: -



• E.g. 18/3 ^ 2 + 4 * 2

18/9 + 4 * 2

2 + 4 * 2

2 + 8

10



E.g. 3 * 9 mod 2 ^2 + 5\4.8/2-3 3 * 9 mod 4 + 5\4.8/2-3

27 mod 4 + 5\4.8/2-3 27 mod 4 + 5\4.8/2-3

27 mod 4 + 5\2.4-327 mod 4 +2-3

3 + 2 -35 -3

2



e.g. (2-3*4/5)^2 + 5/(4*3 -2^3)(2-3*4/5)^2 + 5/(4*3 -2^3)(2-12/5)^2 + 5/(4*3 -2^3)(2-2.4)^2 + 5/(4*3 -2^3)(-0.4)^2 + 5/(4*3 -2^3)-0.4^2 + 5/(4*3 -2^3)-0.4^2 + 5/(4*3 -8)-0.4^2 + 5/(12 -8)

-0.4^2 + 5/(4)-0.4^2 + 5/40.16 + 5/4

0.16 + 1.251.41


Random number

e.g.Dim ran As New Random()T1.Text = ran.Next(0, 10)

• chooses number randomly >=0 and <10 (note that 10 is not included)

• e.g.Dim ran As New Random()T1.Text = ran.Next(10, 10)

• t1.text contains 10


Coding a Form Load Event Procedure• Executes when the form first loads into

memory


Coding the btnReset_Click Event Procedure• Click the Form1.vb[Design] tab and then

double-click the btnReset control. Enter the 7 lines of code below. Do not press the ENTER key when finished


Using the Option Strict Statement

• Instructs Visual Basic .NET to force you to ensure that all assignment statements use the same data type on both sides of the assignment

• In the code window on line 1, type Option Strict On


Declaring Global Variables


Declaring Global Variables

• Click the end of line 195 and then press the ENTER key. Enter the line of code below, and do not press the ENTER key


Coding the Event Procedures for the RadioButton Controls• Enter the code below on their respective

lines:


Declaring Local Variables

• Click the Form1.vb[Design] tab and then double-click the btnComputePayment control. Enter the code below in the code window. Do not press ENTER after entering the last line


Converting Data Types

• Press the ENTER key twice. Enter the line of code below and do not press ENTER




Construction of Error-Free Numeric Expressions


Coding an Expression to Calculate a Monthly Interest Rate• Press the ENTER key twice. Enter the

lines of code below and do not press the ENTER key


Intrinsic Functions

• Ddb()• Fv()• Lpmt()• Lrr()• Mirr()• Nper()

• Npv()• Ppmt()• Pv()• Rate()• Sin()• Syd()• pmt()

These functions are only for knowledge it is not required from you to know the detail of functions.

لالطالع فقط


The Pmt Functionلالطالع فقط


Using the Pmt Function

• Press the ENTER key twice. Enter the lines of code below and do not press the ENTER key

لالطالع فقط


The Format$ Function


Using the Format$ Function

• Press the ENTER key. Enter the lines of code below and do not press the ENTER key


Finishing the Project

• Save the project– Click the Save All button on the Standard

toolbar

• Test the project using test data and verify your output

• Document the application using your knowledge from Chapter 2

• Quit Visual Basic .NET


Summary

• Use the RadioButton and GroupBox controls

• Set a default button on a form

• Declare variables and constants


Summary

• Use variables and constants within code

• Describe Visual Basic .NET data types

• Convert between data types

• Code a form Load event procedure

• Use the Option Strict statement


Summary

• Use arithmetic expressions

• Describe the order of operator precedence in code

• Use the Pmt function

• Use the Format$ function

Visual Basic .NETComprehensive Concepts

and Techniques

Chapter 4 Complete

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Visual Basic.NET Comprehensive Concepts and Techniques Chapter 4 Working with Variables, Constants, Data Types, and Expressions