itp 150 week 4 variables. itp 150 - lecturer: a. borquez2 review: controls propeties events ...

ITP 150ITP 150

Week 4

Variables

ITP 150 - Lecturer: A. Borquez 2

Review: Controls Propeties Events Methods Procedures Functions

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Controls for Displaying andEntering Text

To provide this feature Use 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

Controls That Present Choices to Users

To provide this feature Use 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 feature Use 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

To perform this task Use this method or statementLoad a form into memory,but do not display it

Load statement, or you can reference aproperty or control on the form

Load and display a form Show methodDisplay a loaded form Show methodHide a form from view Hide methodHide a form from view andunload from memory

Unload statement


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:

Dim variablename [As type]


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.


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.


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.


Variable Data Types

Data type Storage size

Byte 1 byte

Boolean 2 bytes

Integer 2 bytes

Long (long integer) 4 bytes

Single (single floating-point) 4 bytes

Double(double floating-point) 8 bytes

Currency (scaled integer) 8 bytes

Date 8 bytes

Object 4 bytes + size of object

String (variable-length) 10 bytes + string length

String (fixed-length) length of string

Variant 16 bytes

Data type Storage size

Byte 1 byte

Boolean 2 bytes

Integer 2 bytes

Long (long integer) 4 bytes

Single (single floating-point) 4 bytes

Double(double floating-point) 8 bytes

Currency (scaled integer) 8 bytes

Date 8 bytes

Object 4 bytes + size of object

String (variable-length) 10 bytes + string length

String (fixed-length) length of string

Variant 16 bytes


Variable Data Types Naming Conventions

Data type Prefix

Byte bytBoolean blnInteger intLong lngSingle sngDouble dblCurrency curDate dtmObject objString strVariant var

Data type Prefix

Byte bytBoolean blnInteger intLong lngSingle sngDouble dblCurrency curDate dtmObject objString strVariant var

Understanding the Scope of Variables

Scope Private Public

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 to Variables 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.


Working with Date and Time

Dim dtNewDate As DatedtNewDate = dtDate + 5

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

Now, Date, and Time functions


VB Date/Time Functions

Function Example Value displayed

Year() Year(Now) 1999Month() Month(Now) 2Day() Day(Now) 22Weekday() Weekday(Now) 7Hour() Hour(Now) 11Minute() Minute(Now) 38Second() Second(Now) 9

The DateDiff Function

The DateDiff function returns the number of time intervals between two dates.

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

Dim dtTheDate As DateDim strMsg As String

dtTheDate = InputBox("Enter a date")strMsg = "Days from today: " & DateDiff("d", Now, dtTheDate)MsgBox strMsg

VB Format Functionthe Format function accepts a numeric value and converts it to a string

Format syntax Result

Format(Now, “m/d/yy”) 1/27/99Format(Now, “dddd, mmmm dd, yyyy”) Wednesday, January 27, 1999Format(Now, “d-mmm”) 27-JanFormat(Now, “mmmm-yy”) January-99Format(Now, “hh:mm AM/PM”) 07:18 AMFormat(Now, “h:mm:ss a/p”) 7:18:00 aFormat(Now, “d-mmmm h:mm”) 3-January 7:18

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

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

Using Named Formats


Sub Procedures vs. Function Procedures

Sub procedures do not return a value.

Function procedures return a value.

Sub procedures do not return a value.

Function procedures return a value.


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.

• 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]Sub procedurename (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

• 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

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.

•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.

[Private|Public][Static]Function procedurename (arguments) [As type]statements

itp 150 week 4 variables. itp 150 - lecturer: a. borquez2 review: controls propeties events ...

Documents

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type slide

variable issues

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line control slide

application variables

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