data types operators and variables

7/28/2019 Data Types Operators and Variables

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Variables & Data Types

Variable- are placeholders used to store values in

Main memory

The data types of variables determine how the bit

representing these values are stored

in the computer memory

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Naming a Variable

They may include only letters, numbers, and underscore (_)

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.

No more than 255 characters

You cannot use a reserved word

(word needed by Visual Basic)

The first character must be a letter



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Cont..

Data Types

Data Type Suffix

Boolean NoneInteger %Long (Integer) &

Single (Floating) !Double (Floating) #Currency @Date NoneObject None

String $Variant None



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Data type Description Range

Byte 1-byte binary data 0 to 255

Integer 2-byte integer 32,768 to 32,767

Long 4-byte integer 2,147,483,648 to

2,147,483,647

Cont..



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Single 4-byte floating-point number

Range

Negative values

3.402823E38 to1.401298E45

Positive values

1.401298E45 to 3.402823E38

Single

Cont..



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8-byte floating-point number

RangeNegative values

1.79769313486231E308 to4.94065645841247E324

Positive values

4.94065645841247E324 to 1.79769313486231E308

Double

Cont..



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Currency

8-byte number with fixed decimal point

Range

922,337,203,685,477.5808 to 22,337,203,685,477.5807

Cont..



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String of characters Zero to approximately two billion

characters

Variant , Date/time, floating-point number, integer, string,

or object. 16 bytes, plus 1 byte for each character if a

string value.

String

Cont..



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Boolean 2 bytes True or False

Date 8-byte date/time value

January 1, 100 toDecember 31, 9999

Object 4 bytes Any Object reference

Cont..



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Data Types

Constant a fixed value

Eg PI as constant declaration

Cont..



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Variable declaration

There are three ways for a variable to be declared

Default

Implicit

Explicit



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Implicit Declaration

Visual Basic automatically creates a variablewith that name, which you can use as if you had

explicitly declared it.

While this is convenient, it can lead to subtleerrors in your code if you misspell a variable

name.

For example, suppose this was the

function you wrote:



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You don't have to declare a variable before using it.

Private Sub Command1_Click()Quantity = 20SalesPrice = 200.00Tax = 50Total = Quantity * SalesPrice + Txa

Print "Quantity", "SalesPrice", "Total Price"Print Quantity, SalesPrice, Total

End Sub

Cont..



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Explicit Declaration

Because of these advantages,it is a good programmingpractice that declares all variables as explicit

There are many advantages to explicitly typing variableswe ensure all computations are properly done,mistyped variable names are easily spotted

Visual Basic will take care of ensuring consistencyin upper and lower case letters used in variable names.



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To avoid the problem of misnaming variables,declared explicitly as a variable

To explicitly declare variables

Place this statement in the Declarationssection of a class, form, or standard module:Option Explicit

Cont..



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This automatically inserts the Option Explicit statement

in any new modules,

From theTools menu, choose Options, click theEditor tab

and check the Require Variable Declaration option.

but not in modules already created;

therefore, you must manually add Option Explicit to any

existing modules within a project.

Cont..



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Variable scope

To explicitly type a variable,you must first determine its scope.There are four levels of scope:

Procedure level

Procedure level, static

Form levelLocal Level

Global Level module level



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Within a procedure, variables are declared usingthe Dim statement:

Dim NoOfStudent as Integer

Dim Salary as Double

Dim StName, StCity as String

Note :- StName is taken as Variant type and

StCity is taken as String



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Within a procedure, variables are declared usingthe Dim statement:

Dim MyInt%

Dim MyDouble#

Dim MyString$, YourString$

Using Suffix Characters



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?Private Sub Command1_Click();Dim Quantity as IntegerDim Name as String NameQuantity

0



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Private Sub Command1_Click();Dim Quantity as Integer

Dim Name as String Name

Name =Saman

QuantitySaman



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Dim Name as String Name

Name =Saman

QuantitySaman

Quantity =23

23



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Dim Name as String

Name =Saman

Quantity =23

NameQuantitySaman23

Endsub



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YX

17 5

Dim X as Integer

X=17

Y=5

Private Sub Command1_click();

ENDSub

X=X+2

MemoryDim Y as Integer



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YX

19 5

Dim X as Integer

X=17

Y=5

Private Sub Command1_click();

ENDSub

X=X+2

MemoryDim Y as Integer



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Variable Scope

To make a procedure level variable retainits value upon exiting the procedure,

replace the Dim keyword with Static:

Static MyInt as Integer

Static MyDouble as Double



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Variable Scope

Form level variables retain their value andare available to all procedures within that form.Form level variables are declared in the declarations

part of the general object in the form's codewindow.The Dim keyword is used:

Dim MyInt as IntegerDim MyDate as Date



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Variable Scope

Global level variables retain their value and areavailable to all procedures within an application.Module level variables are declared in the

declarations part of the general object of amodule's code window.(It is advisable to keep all global variables in one module.)Use the Global keyword orPublic Keyword:

Global MyInt as IntegerPublic MyDate as Date

Global level variables



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Operators

3. Comparison Operators

4. Logical Operators

2. String-Concatenate Operators

1. Arithmetic. Operators

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Operator Operation

^ Exponentiation

* / Multiplication and division\ Integer division (truncates)

Mod Modulus

+ - Addition and subtraction

Arithmetic. Operators

Parentheses around expressions can change precedence.


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Unary High

+,- lowest

Operator precedence

If an expression is written 16+20*4-18/3

how would it be evaluated?There is a set rule to be followed

1.All operations are carried out left to right.

2.All operators have associated hierarchies

that determine the order of precedence inevaluating the expression.

*, /, MOD,



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y = 6 * 4 / 3 * 2

Evaluated

First

y = 24 / 3 * 2EvaluatedSecond

y = 8 * 2 Evaluated

Thirdy=16

y = 6 * 4 / 3 * 2



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Private Sub Command1_Click()

Print 21 + 2

Print 21 - 2

Print 21 / 2Print 21 \ 2

Print 21 Mod 2

Print 2 ^ 2

Print 8 ^ 2 / 3

Print 8 ^ (2 / 3)

End Sub

Print 8 ^ (2 / 3)



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Write following expression in VB

1. x2+2x-5

2. 2x2-3x/(y-7)

3. 5x-2/(3x2-

7)



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Comparison Operators

Operator Comparison> Greater than< Less than

>= Greater than or equal to


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Print 3 = 4


End Sub

Print 3 > 4

Print 3 < 4Print 3 >= 3

Print 3


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String-Concatenate Operators

String -Concatenate Operators

To concatenate two strings, use the & symbol

or the + symbol:

lblTime.Caption = "The current time is" &Format(Now, hh:mm)

txtSample.Text = "Hook this + to this



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Logical Operators Cont.

Three logical operators

Operator Operation

Not Logical not

And Logical and

Or Logical or



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Logical Operators

Three logical operators

The Not operator simply negates an operand.

The And operator returns a True if both operandsare True. Else, it returns a False.

The Or operator returns a True if either of itsoperands is True, else it returns a False.

Logical operators follow arithmetic operators inprecedence



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Print Not (3 = 4)

Print 3 = 4 And "A" = "B"

Print 3 = 4 Or "A" = "B"

End Sub

False

True

False



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Variable Scope *Example of Variable Scope:

Global X as IntegerForm1 Form2

Sub Routine1()Sub Routine3()

Sub Routine2()

Static B as Double.

.End Sub

Dim A as Double

End Sub

Dim Y as Integer Dim Z as Single

Dim C as Double

Module1

Procedure Routine1

has access to

X, Y, and

A (loses value upon termination)

Procedure Routine2

has access to

X, Y, and B (retains value)

Procedure Routine3has access to

X, Z, and

C (loses value upon termination)

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