02. data type and variables

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Data Types and Data Types and Variables Variables Doncho Minkov Doncho Minkov Telerik Software Telerik Software Academy Academy http://academy.telerik.com http://academy.telerik.com Technical Trainer Technical Trainer http://minkov.it http://minkov.it

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Page 1: 02. Data Type and Variables

Data Types and Data Types and VariablesVariables

Doncho MinkovDoncho Minkov

Telerik Software Telerik Software AcademyAcademyhttp://academy.telerik.com http://academy.telerik.com

Technical TrainerTechnical Trainerhttp://minkov.it http://minkov.it

Page 2: 02. Data Type and Variables

Table of ContentsTable of Contents

1.1. Data TypesData Types Integer Integer Floating-Point Floating-Point BooleanBoolean StringString

2.2. Declaring and Using VariablesDeclaring and Using Variables IdentifiersIdentifiers Declaring Variables and Assigning Declaring Variables and Assigning

ValuesValues

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Data TypesData Types

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How Computing Works?How Computing Works?

Computers are machines that Computers are machines that process dataprocess data Data is stored in the computer Data is stored in the computer

memory in memory in variablesvariables

Variables have Variables have namename, , data type data type and and valuevalue

Example of variable definition and Example of variable definition and assignment in JavaScriptassignment in JavaScript

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var count = 5;var count = 5;

Variable nameVariable name

Variable Variable valuevalue

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What Is a Data Type?What Is a Data Type? A A data typedata type::

Is a domain of values of similar Is a domain of values of similar characteristicscharacteristics

Defines the type of information Defines the type of information stored in the computer memory (in stored in the computer memory (in a variable)a variable)

Examples:Examples:

Positive integers: Positive integers: 11, , 22, , 33, , ……

Alphabetical characters: Alphabetical characters: aa, , bb, , cc, , ……5

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JavaScript Data TypesJavaScript Data Types JavaScript is actually typeless JavaScript is actually typeless

languagelanguage i.e. the type of a variable can be i.e. the type of a variable can be

changedchanged

All the variables are declared with All the variables are declared with varvar

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var count = 5; //variable holding integer valuevar count = 5; //variable holding integer valuevar name = "Doncho Minkov"; //variable holding a var name = "Doncho Minkov"; //variable holding a stringstringvar mark = 5.25 //variable holding floating point var mark = 5.25 //variable holding floating point numbernumber

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Integer TypesInteger Types

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What are Integer What are Integer Types?Types?

Integer types:Integer types: Represent whole numbersRepresent whole numbers

Have range of values, depending on Have range of values, depending on the size of memory usedthe size of memory used

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Integer Types - ExampleInteger Types - Example

Integer type can hold numbers Integer type can hold numbers from from --90071992547409929007199254740992 toto 90071992547409929007199254740992

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var studentsCount = 5;var studentsCount = 5;

var maxInteger = 9007199254740992;var maxInteger = 9007199254740992;

var minInteger = -9007199254740992;var minInteger = -9007199254740992;

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Integer TypesInteger TypesLive DemoLive Demo

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Floating-PointFloating-Point

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What are Floating-Point What are Floating-Point Types?Types?

Floating-point types:Floating-point types:

Represent real numbersRepresent real numbers

Have range of values and precisionHave range of values and precision

Can behave abnormally in the Can behave abnormally in the calculationscalculations

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Floating-Point TypesFloating-Point Types

Floating-point size depend on the Floating-point size depend on the platformplatform the browser and the OSthe browser and the OS

32-bit OS and browser have 32 bits 32-bit OS and browser have 32 bits for number, while 64-bit have 64 bitsfor number, while 64-bit have 64 bits It is good idea to use up to 32-bit It is good idea to use up to 32-bit

numbersnumbers Will always work on all platformsWill always work on all platforms

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Abnormalities in the Abnormalities in the Floating-Point Floating-Point

CalculationsCalculations Sometimes abnormalities can be Sometimes abnormalities can be

observed when using floating-point observed when using floating-point numbersnumbers Comparing floating-point numbers Comparing floating-point numbers

can not be performed directly with can not be performed directly with the the ==== operator operator

Example:Example:

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var a = 1.0;var a = 1.0;var b = 0.33;var b = 0.33;var sum = 1.33;var sum = 1.33;var equal = (a+b == sum); // False!!!var equal = (a+b == sum); // False!!!console.log("a+b = "+ (a+b) + ", sum = "+ console.log("a+b = "+ (a+b) + ", sum = "+ sum + ", sum == a+b? is " + equal);sum + ", sum == a+b? is " + equal);

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Floating-Point and Floating-Point and Decimal Floating-Decimal Floating-

Point TypesPoint TypesLive DemoLive Demo

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Boolean TypeBoolean Type

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The Boolean Data TypeThe Boolean Data Type

The The Boolean data typeBoolean data type:: Has two possible values: Has two possible values:

truetrue and and falsefalse

Is useful in logical expressionsIs useful in logical expressions

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Boolean Values – Boolean Values – ExampleExample

Example of boolean variables Example of boolean variables taking values of taking values of truetrue or or falsefalse::

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var a = 1;var a = 1;var b = 2;var b = 2;

var greaterAB = (a > b);var greaterAB = (a > b);

console.log(greaterAB); // Falseconsole.log(greaterAB); // False

var equalA1 = (a == 1);var equalA1 = (a == 1);

console.log(equalA1); // Trueconsole.log(equalA1); // True

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Boolean TypeBoolean TypeLive DemoLive Demo

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String TypeString Type

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The String Data TypeThe String Data Type The The string data typestring data type::

Represents a sequence of Represents a sequence of characterscharacters

Strings are enclosed in quotes:Strings are enclosed in quotes: Both Both '' and and "" work work

Strings can be concatenatedStrings can be concatenated Using the Using the ++ operator operator

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var s = "Microsoft .NET Framework";var s = "Microsoft .NET Framework";

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Saying Hello – ExampleSaying Hello – Example Concatenating the two names of a Concatenating the two names of a

person to obtain his full name:person to obtain his full name:

NOTE: a space is missing between NOTE: a space is missing between the two names! We have to add it the two names! We have to add it manuallymanually 22

var firstname = "Ivan";var firstname = "Ivan";var lastname = "Ivanov";var lastname = "Ivanov";Console.log("Hello, " + firstname + "!");Console.log("Hello, " + firstname + "!");

var fullName = firstname + " " + lastname;var fullName = firstname + " " + lastname;Console.log("Your full name is " + Console.log("Your full name is " + fullname);fullname);

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String TypeString TypeLive DemoLive Demo

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Introducing Introducing VariablesVariables

pp qq

ii

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What Is a Variable?What Is a Variable? A variable is a:A variable is a:

Placeholder of information that can Placeholder of information that can usually be changed at run-timeusually be changed at run-time

Variables allow you to:Variables allow you to: Store informationStore information

Retrieve the stored informationRetrieve the stored information

Manipulate the stored informationManipulate the stored information

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Variable CharacteristicsVariable Characteristics A variable has:A variable has:

NameName Type (of stored data)Type (of stored data) ValueValue

Example:Example:

Name: Name: countercounter Type: Type: integerinteger Value: Value: 55

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var counter = 5;var counter = 5;

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Declaring And Declaring And Using VariablesUsing Variables

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Declaring VariablesDeclaring Variables When declaring a variable we:When declaring a variable we:

Specify its name (called identifier)Specify its name (called identifier)

May give it an initial valueMay give it an initial value

The type is identified by the valueThe type is identified by the value

The syntax is the following:The syntax is the following:

Example:Example:

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var <identifier> [= <initialization>];var <identifier> [= <initialization>];

var height = 200;var height = 200;

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IdentifiersIdentifiers Identifiers may consist of:Identifiers may consist of:

Letters (Unicode) Letters (Unicode)

Digits [0-9]Digits [0-9]

Underscore "_"Underscore "_"

Dollar '$'Dollar '$'

IdentifiersIdentifiers Can begin only with a letter or an Can begin only with a letter or an

underscoreunderscore

Cannot be a JavaScript keywordCannot be a JavaScript keyword29

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Identifiers (2)Identifiers (2) IdentifiersIdentifiers

Should have a descriptive nameShould have a descriptive name

It is recommended to use only Latin It is recommended to use only Latin lettersletters

Should be neither too long nor too Should be neither too long nor too shortshort

Note:Note: In JavaScript small letters are In JavaScript small letters are

considered different than the considered different than the capital letters (case sensitivity)capital letters (case sensitivity)

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Identifiers – ExamplesIdentifiers – Examples Examples of correct identifiers:Examples of correct identifiers:

Examples of incorrect identifiers:Examples of incorrect identifiers:

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var new;var new; // new is a keyword// new is a keywordvar 2Pac;var 2Pac; // Cannot begin with a digit// Cannot begin with a digit

var New = 2; // Here N is capitalvar New = 2; // Here N is capitalvar _2Pac; // This identifiers begins with _var _2Pac; // This identifiers begins with _

var поздрав = "Hello"; // Unicode symbols usedvar поздрав = "Hello"; // Unicode symbols used// The following is more appropriate:// The following is more appropriate:var greeting = "Hello"; var greeting = "Hello";

var n = 100; // Undescriptivevar n = 100; // Undescriptivevar numberOfClients = 100; // Descriptivevar numberOfClients = 100; // Descriptive

// Overdescriptive identifier:// Overdescriptive identifier:var numberOfPrivateClientOfTheFirm = 100;var numberOfPrivateClientOfTheFirm = 100;

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Assigning Assigning Values To Values To VariablesVariables

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Assigning ValuesAssigning Values Assigning of values to variablesAssigning of values to variables

Is achieved by the Is achieved by the == operator operator

The The == operator has operator has Variable identifier on the leftVariable identifier on the left

Value of the corresponding data Value of the corresponding data type on the righttype on the right

Could be used in a cascade calling, Could be used in a cascade calling, where assigning is done from right where assigning is done from right to leftto left

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Assigning Values – Assigning Values – ExamplesExamples

Assigning values example:Assigning values example:

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var firstValue = 5;var firstValue = 5;var secondValue;var secondValue;var thirdValue;var thirdValue;

// Using an already declared variable:// Using an already declared variable:secondValue = firstValue;secondValue = firstValue;

// The following cascade calling assigns// The following cascade calling assigns// 3 to firstValue and then firstValue// 3 to firstValue and then firstValue// to thirdValue, so both variables have// to thirdValue, so both variables have// the value 3 as a result:// the value 3 as a result:

thirdValue = firstValue = 3; // Avoid this!thirdValue = firstValue = 3; // Avoid this!

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Initializing VariablesInitializing Variables

InitializingInitializing

Is assigning of initial valueIs assigning of initial value

Must be done before the variable is Must be done before the variable is used!used!

Several ways of initializing:Several ways of initializing:

By using a literal expressionBy using a literal expression

By referring to an already initialized By referring to an already initialized variablevariable

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Initialization – Initialization – ExamplesExamples

Example of some initializations:Example of some initializations:

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// This is how we use a literal expression:// This is how we use a literal expression:var heightInMeters = 1.74;var heightInMeters = 1.74;

// Here we use an already initialized // Here we use an already initialized variable:variable:var greeting = "Hello World!";var greeting = "Hello World!";var message = greeting;var message = greeting;

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Assigning and Assigning and Initializing Initializing VariablesVariables

Live DemoLive Demo