CHAPTER 3 - Using Variables and Constants

Controls and variables

temporarily store data

Variable

Temporary storage location in main memory. Specified by data type, name, scope, and lifetime

Data type

Specifies type of data a variable can store. Provides a class template for creating variables

Unicode

Universal coding scheme for characters. Assigns unique numeric value to each character in the written languages of the world

Name

Variables are referred to by ____

Identifier

Another term for variable name

Hungarian notation

Use_________ ________, with a three-character prefix representing the variable's data type. Name should be descriptive: e.g., dblLength. Use camel case: e.g., dblSalesAmount

Declaration statement

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

0

default value of declared numeric variable without value

False

default value of declared boolean variable without value

Nothing

default value of declared Object and String variable without value

1/1/0001 12:00:00 AM

default value of declared date variable without value

Assignment statement

Assigns value to variable at run time. 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. Is preferred over Val as it Allows programmer to specify data type

Double

Val only returns a type ______ value

Convert class

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

TryParse

is recommended for converting strings to numeric data types. Will not produce an error if conversion fails

Scope

Indicates where variable can be used

Lifetime

How long variable remains in memory.

Class, procedure, block

3 types of scope

Class

type of scope. Variable can be used by all procedures in a form

Procedure

type of scope. Variable can be used within _________

Block

type of scope. Variable can be used within specific code _____

Procedure, Dim

Variables with _________ scope Can be used only by that procedure. Declared at beginning of procedure. Removed from memory when procedure ends. Declared using Dim keyword

class , Private

Variables with _____ scope. Can be used by all procedures in a form. Declared in form's Declarations section. Remain in memory until application ends Declared using _______ keyword

Static variable

Procedure-level variable with extended lifetime. Remains in memory between procedure calls. Retains its value even when the procedure ends

Static keyword

Used to declare 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

Creates named constant. Stores value of expression in named constant

Expression

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

Option Explicit On

a statement that 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, e.g., Integer to Decimal

Demotion

Data truncated e.g., Decimal to Integer. Data loss can occur when it occurs

Option Infer Off

a statement that Ensures that every variable is declared with a data type

Option Strict On

a statement that Disallows implicit conversions. Type conversion rules are applied when this option is on

Concatenate

Connect strings together

Ampersand

Concatenation operator symbol

Strings

numeric values used with the & operator are converted to _______

InputBox function

Displays dialog box and retrieves user input

ControlChars.NewLine

a constant command. Advances the insertion point to the next line in a control. Also used to advance insertion point in file or on printer

_

Line continuation character

Line continuation character

(_) Used to break up long line 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

Formatting

Specifying decimal places and special characters to display

ToString method

is replacing Format function

Syntax:

variablename.ToString(formatString)

variablename: Name of a numeric variable

formatString: String specifying format you want to use

TextChanged event

Occurs when the Text property value of a control change. Can occur when The user enters data into the control or Code assigns data to the control's Text property

Handles

_______ clause. Appears in an event procedure's header. Indicates object and event associated with procedure