Day04 01 Variables

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By Lanka RodrigoBy Lanka Rodrigo


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OutlineOutline

,

Declaring and using variables Declaring constants

Common data types used in Math

Integers and Doublers (Floating point numbers)

Mathematical o erations

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VariablesVariables A variable is a named piece of memory (Temporary

Which has been specifically reserved for holding data in

A variable is a data box

Variable binds the stored data to a name which enables

convenient access at a letter time

Rules for naming variables

No more than 40 characters

Can only use letters, numbers and underscore (_) characters

The first character must be a letter

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You cannot use the Visual Basic .NET key words (eg. Form, Beep)


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Variables Contd.Variables Contd.

It's variable, the content may vary"

Box that can only contain one thing at a time,

but the content of the box may change over time We use variables to store and keep track of things

May have many boxes, and to keep them apart,

we usually name them separately This is called "variable names

To make sure you can find a contents easily, always name it

so that the name explains what is in the box When you find it, it may turn out to be another,

just with somewhat similar content

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Variables Contd.Variables Contd.

Variables can be assignedvalues,via assignment:

Such an assignment operation takes the form:

Variable Name = New Value

Example:

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Declaration of VariablesDeclaration of Variables

Prior to use, variables must first be declared

This reserves (allocate) a place in computer memory

The VB syntax for a variable declarationDim Variable_Name

DimVariable_NameAsData_Type

Dim (Dimension): keyword for declaring a variable inside a

procedure.

As: Keyword for specifying the data type

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Data T eData T e If you think of a variable as a box for holding data,

.

Name Contains Type

USB_Box USB memory chips SolidMilk_Bottle Milk Liquid

en_ ox ens o

Tea_Bottle Tea Liquid

_

Coin_Box Coins Solid

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Data T eData T e A box's size and shape determine what the box can hold

" " ' y

ome use u a a ypes: Integer Non decimal numbers

String A set of letters or words Boolean True or false

Single Numbers with decimals

DateTime Date and time of day Decimal Decimal numbers

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Data T eData T e We need to handle data such as names, addresses, money, date,

,

Similarly in Visual Basic 2008, have to deal with all sorts of data,

some can be mathematicall calculated

while some are in the form of text or other forms

VB2008 divides data into different t es so that it is easier to

manage when we need to write the code involving those data

Visual Basic 2008 Data Types

Numeric data types andNon-numeric data types

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Numeric DataNumeric Data T eT e Numeric data types are types of data that consist of numbers,

with various standard operators

such as add, minus, multiply, divide and so onType Storage Range of Values

Byte 1 byte 0 to 255

Integer 2 bytes -32,768 to 32,767

- , , , , , ,

Single 4 bytes-3.402823E+38 to -1.401298E-45 for negative values

1.401298E-45 to 3.402823E+38 for positive values.

Double 8 bytes- . e o - . - or nega ve va ues4.94065645841247E-324 to 1.79769313486232e+308 for positive values.

Currency 8 bytes -922,337,203,685,477.5808 to 922,337,203,685,477.5807

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Decimal 12 bytes

+/- 79,228,162,514,264,337,593,543,950,335 if no decimal is use

+/- 7.9228162514264337593543950335 (28 decimal places).


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NonNon--numeric Datanumeric Data T eT e Nonnumeric data types are data that cannot be manipulated

The non-numeric data comprises Text or String, Date, Boolean

Ob ect and Variant data t e

Type Storage Range

,

String(variable length) Length + 10 bytes 0 to 2 billion characters

ate ytes anuary , to ecem er ,

Boolean 2 bytes True or False

Object 4 bytes Any embedded object

Variant(numeric) 16 bytes Any value as large as Double

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Variant(text) Length+22 bytes Same as variable-length string


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Exam le of Variable UseExam le of Variable Use

Declare three variables as Inte er

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Data Types for NumbersData Types for Numbers When working with numbers, we use two types of data:

Integers (usually take the Integer type): xamp e: , , ,

Useful for discrete math:

counting objects (cardinal) .

ordering objects (ordinal)

Example: The one-hundredth customer will win

Floating point numbers (usually take the Double type): Example: 1.50, 3.1415926, etc have a decimal point

More useful for normal arithmetic

Note: If you do not explicitly declare a variables data type It is declared by the system as an Object, by default

We will talk more about Integers and Floats, and other data types,shortly

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First, lets look at some basic mathematical operations


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ConstantsConstants Assigning avariable fixes a memory location for

storage

However, within limits a variable may take arbitrary

values Depending on the data type (i.e., Integer, Double, etc)

The value of a constant, on the other hand, is fixed.

The VB syntax for declaring a constant is:

ons const_name s ata_ ype= va ue

Const is a keyword declaring the constant; Const_name andvalue are the name and value of the constant;

Data_Type is the type of constant

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Constants Contd.Constants Contd.

This is called

initialization

xamp e: m x s n eger =

Declares Integer variable x, and sets its starting value to 6

ome exam es:

Const x As Integer = 10

onst s ou e = .

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Data T e conversionData T e conversion

In our programs we may want to convert our data type

o a a o e y e. s co ve s o s ca e as

We use CType function for the conversionExamples:

CBool - use this function to convert to Bool data type

CByte - use this function to convert to Byte data type

CChar - use this function to convert to Char data type

CDate - use this function to convert to Date type

CDbl - use this function to convert to Double data type

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Data T e conversionData T e conversion

Examples:

CInt - use this function to convert to Integer data type

CLng - use this function to convert to Long data type

COb - use this function to convert to Ob ect t e

CShort - use this function to convert to Short data type

CSng - use this function to convert to Single data type

r ng - use s unc on o conver o r ng a a ype

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Pro ramPro ram Sim le Messa eSim le Messa e Make a simple program to get a return Message

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Pro ramPro ram Sim le Messa eSim le Messa e

Step 01 Control Arrangements

tep ett ng ropert es

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Mathematical O erationMathematical O eration

The table below contains the operators available for basic math

operation

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Math StatementsMath Statements What does the statement, x = x + 1 do?

Thinking in terms of arithmetic, this is a nonsense statement

Since = is defined as e ualit

But x is never equal to x + 1!

However, if we instead think in VB, it makes perfect sense! emem er = s t e ass gnment operator

Thus, x = x + 1 tells the computer to:

First, get the value stored in variable x

Then, add 1 to this value Lastly, store the result in variable x

,

Dim x As Integer = 10

x = x + 1

ur ng run- me, e r g s e s rs eva ua e o y e

Then, this result (11) ispassed to the left side (x)

So, the overall result is to set:

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x = 11


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Assignment OperatorsAssignment Operators

Simple one-variable expressions, such as:

Are really assignment operations,

Short-hand operators exist for such operations:

Which combine both o erators into a sin le assi nment

operation For instance, the statement,

n = n + 8 can be written as: n += 8

Either form assigns the valuen + 8

to the variable n

Short-hand operators exist for all 4 basic operations:

+=, -=, *=, /=

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Math Statements (Contd.)Math Statements (Contd.) More generally, a math statement takes the form:

left_side = right_side

Where, left_side is a variable

While right_side is a mathematical expression. t run-t me, t e r g t_s e s eva uate

And thenpassed to the left_side

For instance as a result of the statement: z = 2 * 3

First, the right side is evaluated (yielding 6) Then, the result is passed to z (setting z equal to 6)

What about a compound statement (several math ops):x = 3 * 2 + 1 ?

x = 6 + 1 = 7

If we add first, we get :

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x = =

Which is correct?


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Operator PrecedenceOperator Precedence

In VB, the order of evaluation of math operators is determined by

precedence

For arithmetic, the order of evaluation is (first to last):

Exponentiation (^)

,

Such as the - in x = -6

Multiplication and floating-point division (*, /)

Integer division (\)

Modulus arithmetic (Mod)

Addition and subtraction +,

Note that operations on strings come next (more, later):

String concatenation (+)

tr ng concatenat on &

So, for our example:

x = 3 * 2 + 1

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= 6 + 1 = 7


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Overriding PrecedenceOverriding Precedence

VBs default operation order can be over-ridden easily!

In particular, operations enclosed byparenthesis are evaluated

first Examples:

Our example, stated as: z = 3 * (2 + 1) = 3 * 3 = 9

However, stated as: y = (3 * 2) + 1 = 6 + 1 = 7

Thus, parenthesis provide simpleprogram control, during execution

Parentheses inside of parentheses

The most internal operations are performed first Example: X = (((2 + 1) * 3) + ((7 + 6) 4)) * 5

= ((3 * 3) + (13 -4)) * 5

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= 18 * 5= 90


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StrStr and Val Functionand Val Function

Anathematic operators an only work with numbers. But

The result of arithmetic operations is a number. But the

Text ro ert of a label control where we want to dis lathese results) is a string type

We need to convert strin to number and number to strin

Val Function

Convert string type variable to a numeric value

Str Function Convert numeric value to string

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ConclusionConclusion In this lecture, we have discussed:

Declaration and Use of Variables Declaring Constants

Common Data Types for mathematics Inte ers and Doubles

Mathematical Operations arithmetic operators

assi nment o erators

precedence

Algorithm Design

And Implemented two Programs, using Visual Studio .NET:A. Simple Calculator

B. Price Calculator

With the remainder of the lecture, you should practice: Try creating the programs yourself

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Pro ramPro ram Sim leSim le CalculatorCalculator Make a simple program to implement these

Step 01 Control Arrangements

Step 02 Setting Properties

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Sim le Calculator Contd.Sim le Calculator Contd.

Step 03 Add Codes for all 8 Buttons

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Programming I Microsoft Visual Studio 2008

DISCUSSION TIME

Programming I by Lanka Rodrigo


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Acknowled ementAcknowled ement

This note is prepared jointly with Dr. Nishantha Giguruwa r g na re erence, y r. o n ose

Lanka RodrigoLanka Rodrigo -- Programming IProgramming I

Documents

Day04 01 Variables