data type, variables

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DATA TYPE,VARIABLES AND

CONSTANTS

Chapter 21


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Learning Objectives

By the end of this class, students should be able to :

Identify the various Visual Basic data types.

Use data types in programme.

Define local, module and global variable.

Use local, module and global variable.

Use constant in application.

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Variables

Variables are named locations in memory (memorycells) in which we store data that will change at runtime. One value can be stored in a memory cell. If you put a new value in a memory cell, the old value will be

destroyed.

Variable names in VB: Are used to identify variables. Are different from the value of a variable. Must begin with letter and can use 0-9 in name. Cant include period, but can contain an underscore. Cant be over 255 characters. Not case-sensitive, but suggest using upper and lower case. Should not be a Visual Basic key word.

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Variables (Cont.)

Example mnemonic variable names : sngProfitMargin

for Profit margin

curTaxes for taxes on this price

curAmountDue

for sum of price and taxes

curYTDEarnings for year to date earnings

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Data Types

Data types indicates what types of information will bestored in the allocated memory space.

Two primary types of data: numeric and string (non-numeric).

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2 categories :

Integer numbers without decimals.

e.g : 823 or -4560

Decimals numbers with decimal points.e.g : 8.23 or -400.25

Integers and decimals are stored differently inside

Visual Basic.Net and they are treated differently.e.g : -7 is not same as -7.00

Numeric6


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Numeric

Numeric data can be used in arithmeticoperations : 3.154

2300 -34

0.0000354

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String (non-numeric)

Is a non-numeric data consisting of a seriesof none or more characters.

A string may contain numeric digits, but isnever used for calculations.

Example :

Dogs 123-45-6789

Dr. Brown

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Data Types (cont.)

Numeric data types can be subdivided into specific types: Currency

$55,567.78

Integer

255

Single 567.78

long (Integer)

35,455

Double

567.78129086

Boolean True (-1) or False (0)

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Data Types (cont.)

String stores ASCII symbols (text) and numbers that are not used in

mathematical operations, but rather to provide for the input, output,and manipulation of sets of characters

Integers whole numbers (-32,768 to 32,767) Size 2 bytes

Long Integers whole numbers (-2,147,483,648 to 2,147,483,647) Size 4 bytes

Single

fractional numbers to seven significant digits - Size 4 bytes Double fractional numbers to 15 significant digits Size 8 bytes

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Data Types (cont.)

Currency Use with monetary amounts and up to four digits to the right of the

decimal

Date

Use with dates Boolean Use only when the value of a variable is True or False

Variant Variable is assigned this type automatically if you dont declare the

variable as a specific data type, but takes up more memory

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Variable Prefixes

Variable Type Prefix

String str

Integer int

Long Integer lng

Single sng

Double dbl

Currency cur

Date dtm

Boolean bln

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Advantages of Coding Prefixes

Standard allows anyone who reads the code toimmediately determine data type of variable.

Words that are normally reserved words can beused. strPrint

Different objects can practically same name lblAge (label)

txtAge (text box)

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Declaring Variables

Dim (Dimension) statement declares variables by assigning them aname and data type.

Declare ALL variables with the DIMstatement

General form:

Dim as

For example, Dim strHerName as String, sngMyValue as Single

Dim curAmountDue as Currency

* You can combine variable declarations in one Dim statement,separate by a comma, but you must use theAs Data Type clause foreach variable.

* Example :Dim Total As Integer, Sales As Currency.

*If you fail to declare a variable after the Option Explicit

statement has been entered, an error occurs at Run time

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Option Explicit

Begin ALL Forms with the Option Explicit

command in the declarations procedure of thegeneral object.

This forces all variables to be declared. To automatically include Option Explicit,

go to the Tools|Options|Editor menuselection and check the box for Require

variable declaration.

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Event-driven Input

In VB, we often use event-driven input where data istransferred from text boxes to variables by an event The user, not the program controls the sequence of events

An assignment statementgives a variable a value bysetting it equal either to an existing quantity or to a valuethat can be computed by the program.

Syntax of an assignment statement :

Control property or variable = value, variable, or property

Example : Company = Microsoft

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Assignment Statement

Onlyvariables or controls can be on leftof the =sign statement while thevalue, variable or property

is on the right of the = sign.

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Assignment Statement

sngPi = 3.141592

sngAlpha = 1

sngAlpha = sngAlpha

intN = intN + 1 3 = intN

intN +1 = intN

intN = "Five"

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Comments

To explain the purpose of a statement, a commentstatement is added.

Any statement beginning with an apostrophe ()

or REM (Short for remark)is a comment. Comments can be added before statements or at the

end of statements by using an apostrophe.

Example :

This program displays the current date

or

Rem This program displays the current date

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Simple Calculator20


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Code for command button

Private Sub cmdSum_Click

Declare variablesDim intFirst as Integer, intSecond as Integer

Dim intSum as Integer

Assign values to variablesintFirst = txtFirstNum.Text

intSecond = txtSecondNum.TextEnd Sub

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Functions

Function: Performs an action and returns a value.

an built-in operation that takes one or more more arguments andreturns a a single value.

A Common form of a function is :

variable=functionname(argument1, argument2 )

Not all functions require arguments such as the Date() function.

TheVAL() function is very common and is used to convert the Textproperty from a string to a number, which is assigned to Numericvariable.

E.g :

intQuantity = Val (txtQuantity.Text)

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Using Functions

You cant use text boxes to do computations because the defaultproperty, Text, is a string and therefore must be converted to anumeric value before a calculation is performed.

It is necessary to convert the results of the computation that will

appear in another text box to a string value , using the Str()function, otherwise you would be assigning an integer value to it.

Example functions for converting data:

Val() to convert a string to a number

Str() to convert a number to a string

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Code for Val() function

Private Sub cmdSum_Click()Declare variables

Dim intFirst as Integer,intSecond as Integer

Dim intSum as IntegerAssign values to variables as number

intFirst = Val(txtFirstNum.Text)intSecond = Val(txtSecondNum.Text)

End Sub

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VB Code (Sum Button)

Private Sub cmdSum_Click()Declare variables

Dim intFirst as Integer, intSecond as Integer

Dim intSum as IntegerAssign values to variables as a number

intFirst = Val(txtFirstNum.Text)intSecond = Val(txtSecondNum.Text)intSum = intFirst + intSecondCalculate sum

display sum in sumtext boxtxtSum.Text = Str(intSum)

End Sub

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Break Time!!!!


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Uji Minda!!27

Soalan Pertama:

Anda menyertai perlumbaan. Anda mengejar danmemotong orang yang kedua. Sekarang Andaditempat yang ke berapa?

Jawapan: Jika jawapan anda tempat yang pertama,sudah tentu jawapan anda salah! Jika anda

memotong orang kedua sudah tentu andamengambil tempatnya, tempat kedua!


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28Soalan Kedua :

Bapa Mary ada seramai lima orang anak gadis: 1.Nana, 2. Nene, 3. Nini, 4. Nono. Apakah nama anakgadisnya yang terakhir?

Namanya Mary


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Properties Versus Methods

Dot notation is the way properties are set at run time. Syntax: object.property= value

txtSum.Text=Str(intSum)

The same notation is used to invoke a method for a control.

Methods define the actions a control can carry out.

Methods cant be used in assignment statements.

Syntax: object.method

txtFirstNum.SetFocus

The SetFocus method shifts the cursor to the named text box.

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VB Code (Clear Button)

Private Sub cmdClear_Click()Clear text boxes with empty stringtxtFirstNum.Text = ""

txtSecondNum.Text = ""txtSum.Text = ""

Set focus back to first text boxtxtFirstNum.Setfocus

End Sub

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Using Assignment Statements for Calculations

An expression is a combination of one or morevariables and/or constants with operators.

Aconstantis a quantity that does not change.

Operators are symbols used for carrying outprocessing :

Arithmetic, Comparison, Logical

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Arithmetic Operators

() for grouping (A+B)

^ for exponentiation

Radius ^2 - for negation (subtraction) -Amount

* for multiplication

3 * price / for division PayRaise/Months

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Arithmetic Operators

\ for integer division Divisor, dividend, and quotient are rounded to integers

7.1111\1.95 = 7\2 = 3

modfor modulus Integer remainder of an integer division

7.1111\1.95 = 7\2 = 3 with 1 remainder

+ for addition Price + Taxes

- for subtraction Salary - Deductions

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Examples of valid Expressions

curInterest = curPrincipal * sngIntRate

sngArea = 3.14157 * sngRadius ^2

curUnitCost = curTotalCost / intUnit

intCounter = 0

intCounter = intCounter + 1

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Hierarchy of Operations

1. Operations within parentheses ( )

2. Exponentiation (^)

3. Negation (-)4. Multiplication and division (*,/)

5. Integer division (\)

6. Modulo arithmetic (Mod)

7. Addition and subtraction (+,-)

8. String concatenation (&)

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Arithmetic Example

3 * (Salary - Taxes)^2 + Bonus/Months

Order1 Subtract Taxes from Salary

2 Square the result

3 Multiply this result by 3

4 Divide Bonus by Months

5 Subtract result from first expression

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Arithmetic Examples

Y = 3^2*41*2+3 Y = 37

X = [

X = 6556 sngAverage = ((70 + 80)/2 + 65)/2

sngAverage = 70

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String Operators

For String Variables the only valid operation is thatof combining two strings into one

Use + or & to combine them

strBigday = Christmas + Day strBigday = Christmas & Day

Result of above is Christmas Day

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Symbolic Constants

We can assign a name to a constantwith the Const statement

Examples Const Pi As Single = 3.14157

Const sngIntRate As Single = 0.07

Const intNumYears As Integer = 12

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Vintage Videos40


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Vintage Input-Process-Output

INPUT customer name

video name

video price

PROCESSING taxes = price x tax rate

amount due = price + taxes

OUTPUT taxes amount due

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Pseudocode

Begin Procedure CalculateInput customer nameInput video name

Input video priceTaxes = video price times tax rateAmount due = video price + taxesOutput taxesOutput amount due

End procedure

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Code for Calculate Button

Private Sub cmdCalc_Click()' declaring variables

Const sngTaxRate As Single = 0.07Dim curPrice As Currency, curAmountDue As CurrencyDim curTaxes As Currency

' changing format into currencycurPrice = CCur(txtVideoPrice.Text)curTaxes = curPrice * sngTaxRatecurAmountDue = curPrice + curTaxes

' changing format into text

txtTaxes.Text = Str(curTaxes)txtAmountDue.Text = Str(curAmountDue)

End Sub

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Conversion Functions

ConversionFunction

Purpose

CBool Convert argument to BooleanCCur Convert argument to Currency

CDate Convert argument to Date

CInt Convert argument to Integer

CSng Convert argument to Single

CDbl Convert argument toDouble

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Formatting Data

To display information in a pleasing format, we can use theFormat function:

General form :

variable or control = Format(variable,format expression)

Where the format expressions are in quotes and include;

Currency

Fixed

Standard

Percent

Scientific

E.g :

txtTaxes.Text = Format(curTaxes, currency)

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Calculate button (Revised)

Private Sub cmdCalc_Click()Const sngTaxRate As Single = 0.07Dim curPrice As CurrencyDim curAmountDue As Currency

Dim curTaxes As CurrencycurPrice = CCur(txtVideoPrice.Text)curTaxes = curPrice * sngTaxRatecurAmountDue = curPrice + curTaxestxtTaxes.Text = Format(curTaxes, "Currency")

txtAmountDue.Text = Format(curAmountDue, "Currency")txtVideoPrice.Text = Format(curPrice, "Currency")

End Sub

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Format Commands

Function Description

FormatCurrency Expression formatted as currencyalong with currency symbol

FormatDateTime Expression formatted as a date ortime

FormatNumber Expression formatted as a number

FormatPercent Expression formatted as apercentage with a trailing %

Round Rounds a number a specifiednumber of decimal places

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Code to Clear Entries

Private Sub cmdClear_Click()clear all text boxes

txtCustName.Text = ""

txtVideoName.Text = ""txtVideoPrice.Text = ""txtTaxes.Text = ""txtAmountDue.Text = ""

set focus to this text box

txtCustName.SetFocusEnd Sub

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Some Visual Basic Functions

Abs absolute value

Sqr square root

FV future value of an annuity

PV present value of an annuity

IRR internal rate of return

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Some Visual Basic Functions

Pmt payment to pay off a loan

UCase/Lcase to convert to upper/lower case

Len length of a string

Date

system date DateValue date corresponding to string argument

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Some Examples

txtAnswer.Text = Abs(-3) 3

txtAnswer.Text = Sqr(25)

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txtAnswer.Text = UCase("VB is fun")VB IS FUN

txtAnswer.Text = Len("VB is fun")

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txtAnswer.Text = Sqr(Len("four")) 2

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Monthly Payment Calculator

Assume you wanted to determine the monthly paymentnecessary to pay off a loan at a given interest rate insome number of months Use PMT function

PMT(rate, nper, pv) where:

rate = monthly interest rate

nper = number of months

pv = negativevalue of loan amount

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Th M thl P t F


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The Monthly Payment Form

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C t M thl P t


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Compute Monthly Payment

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Private Sub cmdCompute_Click()Declare variables

Dim curAmount As Currency, intMonths As Integer

Dim sngRate As Single

Dim curPayment As Currency

Convert variables in text boxes

curAmount = CCur(txtAmount.Text)

intMonths = CInt(txtMonths.Text)

Calculate monthly interest rate

sngRate = (CSng(txtRate.Text) / 100) / 12

Calculate payment

curPayment = Pmt(sngRate, intMonths, -curAmount)txtPayment.Text = Format(curPayment, "Currency")

txtAmount.Text = Format(curAmount, "Currency")

End Sub


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EXERCISE

Create and complete the followingcalculation


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Exercise 1 Simple Calculator


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Exercise 2 - Vintage Video57


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Exercise 3 Monthly Payment Calculator


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THaNK YoU

data type, variables

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