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ITP 150. Week 4 Variables. Review:. BackStyleFillColor BorderStyleFillStyle CaptionName EnabledVisible. Controls Propeties Events Methods Procedures Functions. Move Clear SetFocusAddItem. ActivateDragOverLoad ChangeGotFocusLostFocus ClickKeyDownMouseDown

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ITP 150

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ITP 150

Week 4

Variables


Review:

BackStyleFillColor

BorderStyleFillStyle

CaptionName

EnabledVisible

  • Controls

  • Propeties

  • Events

  • Methods

  • Procedures

  • Functions

Move Clear

SetFocusAddItem

ActivateDragOverLoad

ChangeGotFocusLostFocus

ClickKeyDownMouseDown

DblClickKeyPressMouseMove

DragDropKeyUpMouseUp

ITP 150 - Lecturer: A. Borquez


Controls for Displaying andEntering Text

To provide this featureUse this control

Text that can be edited by the user, for example Text box

an order entry field or a password box

Text that is displayed only, for example to identify Label

a field on a form or display instructions to the user

ITP 150 - Lecturer: A. Borquez


Controls That Present Choices to Users

To provide this featureUse this control

A small set of choices from which a user can choose one or Option buttons

more options. Check boxes A small set of options from which (use frames if

a user can choose just one. additional groups are needed)

A scrollable list of choices from which the user can choose. List box

A scrollable list of choices along with a text edit field. Combo box

The user can either choose from the list or type a choice

in the edit field.


Controls That Display Pictures and Graphics

To provide this featureUse this control

A container for other controls.Picture box

Printing or graphics methods. Picture box

Displaying a picture. Image control or picture box

Displaying a simple graphical element Shape or line control


Managing Forms

ITP 150 - Lecturer: A. Borquez


Variables

  • In Visual Basic, you use variables to temporarily store values during the execution of an application

  • Variables have a name (the word you use to refer to the value the variable contains) and a data type (which determines the kind of data the variable can store)

  • To declare a variable is to tell the program about it in advance. You declare a variable with the Dim statement, supplying a name for the variable:Dimvariablename [Astype]

ITP 150 - Lecturer: A. Borquez


Variable rules…...

  • Must begin with a letter.

  • Can't contain an embedded period or embedded type-declaration character.

  • Must not exceed 255 characters.

  • Must be unique within the same scope, which is the range from which the variable can be referenced — a procedure, a form, and so on.

ITP 150 - Lecturer: A. Borquez


Visual Basic Variables

  • Variables: temporarily store values during the

  • execution of an application. Variables have a:

  • name (the word you use to refer to the value the

  • variable contains) and a

  • data type (which determines the kind of data the variable

  • can store).

  • Variables can be used in many ways, including:

    • ®As a counter that stores the number of times a procedure or code

    • block executes.

    • ®As a temporary storage for property values.

    • ®As a place to hold a value returned from a function.

    • ®As a place to store directory or file names.

ITP 150 - Lecturer: A. Borquez


Other Variable issues to think about….

  • Implicit vs. Explicit Declarations

  • Declaring a variable in the Declarations section of a form, standard, or class module, rather than within a procedure, makes the variable available to all the procedures in the module.

  • Declaring a variable using the Public keyword makes it available throughout your application.

  • Declaring a local variable using the Static keyword preserves its value even when a procedure ends.

ITP 150 - Lecturer: A. Borquez


Variable Data Types

Data typeStorage size

Byte1 byte

Boolean2 bytes

Integer2 bytes

Long (long integer)4 bytes

Single (single floating-point)4 bytes

Double(double floating-point)8 bytes

Currency (scaled integer)8 bytes

Date8 bytes

Object4 bytes + size of object

String (variable-length)10 bytes + string length

String (fixed-length)length of string

Variant16 bytes

ITP 150 - Lecturer: A. Borquez


Variable Data Types Naming Conventions

Data typePrefix

Bytebyt

Booleanbln

Integerint

Longlng

Singlesng

Doubledbl

Currencycur

Datedtm

Objectobj

Stringstr

Variantvar

ITP 150 - Lecturer: A. Borquez


Understanding the Scope of Variables

ScopePrivatePublic

Procedure-level Variables are private to Not applicable. You

the procedure in which cannot declare public

they appear. variables within a

procedure.

Module-level Variables are private toVariables are available

the module in which to all modules.

they appear.


Introduction to Procedures

There are two major benefits of programming with procedures:

  • Procedures allow you to break your programs into discrete logical units, each of which you can debug more easily than an entire program without procedures.

  • Procedures used in one program can act as building blocks for other programs, usually with little or no modification.

ITP 150 - Lecturer: A. Borquez


Working with Date and Time

  • Dim dtNewDate As Date

  • dtNewDate = dtDate + 5

  • Now, Date, and Time functions

  • MsgBox "The current date and time is " & Now()

  • MsgBox "The date is " & Date()

  • MsgBox "The time is " & Time()

ITP 150 - Lecturer: A. Borquez


VB Date/Time Functions

FunctionExampleValue displayed

Year()Year(Now)1999

Month()Month(Now)2

Day()Day(Now)22

Weekday()Weekday(Now)7

Hour()Hour(Now)11

Minute()Minute(Now)38

Second()Second(Now)9

ITP 150 - Lecturer: A. Borquez


The DateDiff Function

The DateDiff function returns the number of time intervals

between two dates.

  • DateDiff(interval, date1, date2[, firstdayofweek[, firstweekofyear]])

  • Dim dtTheDate As Date

  • Dim strMsg As String

  • dtTheDate = InputBox("Enter a date")

  • strMsg = "Days from today: " & DateDiff("d", Now, dtTheDate)

  • MsgBox strMsg


VB Format Function

the Format function accepts a numeric value and converts it to a string

Format syntaxResult

Format(Now, “m/d/yy”)1/27/99

Format(Now, “dddd, mmmm dd, yyyy”)Wednesday, January 27, 1999

Format(Now, “d-mmm”)27-Jan

Format(Now, “mmmm-yy”)January-99

Format(Now, “hh:mm AM/PM”)07:18 AM

Format(Now, “h:mm:ss a/p”)7:18:00 a

Format(Now, “d-mmmm h:mm”)3-January 7:18

Using Named Formats

  • txtDate.Text = Format(Now, "Long Date")

  • txtCost.Text = Format(1000, "Currency")


Sub Procedures vs. Function Procedures

  • Sub procedures do not return a value.

  • Function procedures return a value.

ITP 150 - Lecturer: A. Borquez


A Closer Look at Sub_Procedures...

  • A Sub procedure is a block of code that is executed in response to an event.

  • By breaking the code in a module into Sub procedures, it becomes much easier to find or modify the code in your application.

[Private|Public][Static]Subprocedurename (arguments)statements

  • Each time the procedure is called, the statements between Sub and

  • End Sub are executed.

  • Sub procedures can be placed in standard modules, class modules, and form modules.

  • Sub procedures are by default Public in all modules

ITP 150 - Lecturer: A. Borquez


A Closer Look at Functions….

  • Visual Basic includes built-in, or intrinsic functions, like Sqr, Val, or Chr.

  • You can use the Function statement to write your own Function procedures.

[Private|Public][Static]Functionprocedurename (arguments) [Astype]statements

  • Like a Sub procedure, a Function procedure is a separate procedure that can take arguments, perform a series of statements, and change the value of its arguments.

  • Function procedures have data types, just as variables do.

  • You return a value by assigning it to the procedurename itself.


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