Chapter 3: Using Variables and Constants

Controls, Variable

In VB.NET________ and _________ temporarily store data.

data type, name, scope, lifetime

A variable is specified by ________, _________, __________, and __________.

Data type

Specifies type of data a variable can store

Data type

Provides a class template for creating variables

Unicode

Universal coding scheme for characters

Unicode

Assigns unique numeric value to each character in the written languages of the world

Boolean

Basic data types:

It stores a logical value(true, false) and requires 2 bytes

Char

Basic data types:

Stores a Unicode character and requires 2 bytes

Date

Basic data types:

Stores data and time information and requires 8 bytes

Decimal

Basic data types:

Stores a number with a decimal place and requires 16 bytes

Double

Basic data types:

Stores a number with a decimal place and requires 8 bytes

Integer

Basic data types:

Stores a number and requires 4 bytes

Long

Basic data types:

Stores a number and requires 8 bytes

Object

Basic data types:

Stores a data of any type and requires 4 bytes

Short

Basic data types:

Stores a number and requires 2 bytes

Single

Basic data types:

Stores a number with decimal place and requires 4 bytes

String

Basic data types:

Stores text of 0 to approximately 2 billion characters

Variable

It is used to store information and are referred to by name

Identifier

Another term for variable name

Hungarian Notation, three-character prefix

Naming Variables: Use _____________, with a ____________________ representing the variable’s data type

Descriptive

Naming Variables: Name should be __________

Camel case

Naming Variables: Use _______________: e.g., dblSalesAmount

letter, underscore

Naming Variables: The name must begin with a _________ or an ____________

punctuation characters, special characters, spaces

Naming Variables: The name can contain only letters, numbers, and the underscore character. No _________________, __________________, or _________ are allowed in the name.

32

Naming Variables: Although the name can contain thousands of characters, _____ characters is the recommended maximum number of characters to use.

reserved

Naming Variables: The name cannot be a __________ word, such as Sub or Double

Declaration Statement

Used to declare (create) a variable and reserve space in memory for it

Default Value

If no initial value is given to variable when declaring it, computer stores the _______________.

• Numeric variables are set to 0

• Boolean variables are set to False

• Object and String variables are set to Nothing

• Date variables are set to 1/1/0001 12:00:00AM

Assignment Statement

Assigns value to variable at run time

Assignment Statement

Expression may include literal constants, object properties, variables, keywords, arithmetic operators

Literal Constant

Data item whose value does not change

Literal type character

Forces literal constant to change data type

TryParse method

Converts string to number

Val

TryParse is preferred over ______

Double

Val only returns a type ______ value

TryParse

Allows programmer to specify data type

dataType.TryParse(string, numericVariableName)

Syntax of TryParse

Convert Class

Can be used to convert a number from one type to another

TryParse

________ is recommended for converting strings to numeric data types

TryParse Method

Method that will not produce an error if conversion fails

Convert.method(value)

Syntax of Convert class

Scope

Indicates where variable can be used

Lifetime

It is how long a variable remains in memory

Scope and Lifetime

these are determined by where variable is declared

Class: Variable can be used by all procedures in a form

Procedure: Variable can be used within procedure

Block: Variable can be used within specific code block

Three types of scope

Can be used only by that procedure

Declared at beginning of procedure

Removed from memory when procedure ends

Declared using Dim keyword

Four things to remember for variables with procedure scope

Can be used by all procedures in a form

Declared in form’s Declarations section

Remain in memory until application ends

Declared using Private keyword

Four things to remember for variables with class scope

Static variable

Procedure-level variable with extended lifetime

Static variable

Remains in memory between procedure calls

Static variable

Retains its value even when the procedure ends

Static keyword

Used to declare static variable

Static variable

___________ act like class-level variables but have narrower scope. Can only be used within procedure where declared

Named constant

Memory location inside computer whose contents cannot be changed at run time

Const statement

This creates a named constant

Const statement

Stores value of expression in named constant

expression: Can be literal constant, another named constant, or an arithmetic operator

Cannot contain a variable or method

Const constantName As dataType = expression

Syntax of named constant

Option Explicit On

This prevents you from using undeclared variables

Implicit type conversion

Converts right-side value to the data type of left side

Promotion

Data converted to greater precision number

Demotion

Data us truncated and data loss can occur when it happens

Option Infer Off

Ensures that every variable is declared with a data type

Option Strict On

Disallows implicit conversions

Type conversion rules are applied when this option is on

{Dim | Private | Static}

Declare a variable using the following keywords:

Option Explicit On

Enforces full variable declaration

Option Infer Off

Enforces that variables are declared with data types

Option Strict On

Suppresses implicit type conversions

Concatenate

Connect strings together

Concatenation operator

Ampersand (&) is used as a?

strings

Numeric values used with the & operator are converted to ________

InputBox function

Displays dialog box and retrieves user input

prompt

Message to display inside dialog box

title

Text to display in the dialog box’s title bar

defaultResponse

Text to be displayed in the input field

Returned

________ value most often assigned to String variable

InputBox(prompt[, title][, defaultResponse])

Syntax of the InputBox function

ControlChars.NewLine constant

Advances the insertion point to the next line in a control

ControlChars.NewLine constant

This is also used to advance insertion point in file or on printer

String concatenation

ControlChars.NewLine can be used in _________ _____________

Line continuation character (_)

Used to break up long lines of code into two or more lines

Default Button

Button that is activated by pressing Enter key

Button is not required to have the focus

Only one per form

Default button

this button should be button used most often by the user

destructive, irreversible

If the default button’s task is _________ and _________, such as deleting data, it should not be the most often button clicked by the user

Formatting

Specifying decimal places and special characters to display

ToString Method

Formatting numbers to strings method

variablename.ToString(formatString)

Syntax of ToString method

format String

it has a form of Axx specifying a format and precision specifier

AcceptButton

Set default button in form’s ___________ property

TextChanged event

Occurs when the Text property value of a control changes

text

This event can occur when:

The user enters data into the control

Code assigns data to the control’s ___ property

Handles

Appears in an event procedure’s header

Handles clause

Indicates object and event associated with procedure

Handles

Can associate an event procedure with more than one object and/or event

commas

In Handles section of procedure header, list each object and event, separated by _________