Variables Assignment And Operators

variables, assignment and operators

Thursday, September 10, 2009

variablescontainers to store information

that can be used laterhttp://www.w3schools.com/JS/js_variables.asp


http://www.w3schools.com/JS/js_variables.asp

http://www.w3schools.com/JS/js_variables.asp

Remember Algebra?5 = x + 3


varvar a;var age = 5;var name = 'John Nunemaker';


declaring variablesonly need var once, but multiple times won’t hurt you

// goodvar age = 15;age // 15age = 16;age // 16age = 17;age // 17

// no pointvar age = 15;age // 15var age = 16;age // 16var age = 17;age // 17


undeclared variablesautomatically declare, but don’t do this

x = 10;foo = 'bar';

x // 10foo // "bar"


variables can store anything

var age = 15;var name = 'John';var colors = ['red', 'green', 'blue'];var person = {name:'John', age:15};var cool = true;var foo = function() { return 'bar';}


naming variablescase sensitive

var car = 'Ford';var cAr = 'Toyota';

car // "Ford"cAr // "Toyota"


naming variablesmust begin with letter or underscore

var car; // good!var car9; // good!var _car; // good!var 9car; // bad! SyntaxError


naming variablescan be short or descriptive

var x; // shortvar field; // descriptive


naming variablesseparate words with underscores

var section_field_name; // good ideavar sectionfieldname; // bad idea


naming variablesgeneral formatting rules for easier reading

var age = 15; // good ideavar age=15; // bad ideavar age = 15; // bad idea


(pause for review and applause)


good or bad?var section;


good or bad?var section;


good or bad?var 10thingsihateaboutyou;


good or bad?var 10thingsihateaboutyou;

variables cannot start with numbers and should have underscores between words


good or bad?var fieldname;


good or bad?var fieldname;

Should be: var field_name;


good or bad?var section_field_name;


good or bad?var section_field_name;


operatorsassignment and comparison

http://www.w3schools.com/JS/js_operators.asp




arithmetic operators

operator meaning example result

+ addition 5 + 5 10

- subtraction 5 - 4 1

* multiplication 2 * 5 10

/ division 1 / 4 0.25

% modulus 5 % 4 1

++ increment x++ x + 1

-- decrement x-- x - 1


assignment operators

operator example result same as

= var a = 5; 5

+= a += 5; 10 a = a + 5;

-= a -= 5; 0 a = a - 5;

*= a *= 2; 10 a = a * 2;

/= a /= 2; 2.5 a = a / 2;

%= a %= 4; 1 a = a % 4;


comparison operators


equal to value 5 == 5 TRUE

equal to value and type

true === 1 FALSE

!= not equal 5 != 4 TRUE

> greater than 5 > 4 TRUE

< less than 5 < 4 FALSE

>=greater than or equal to

5 >= 5 TRUE

<=less than

or equal to5 <= 5 TRUE

==

===

http://www.w3schools.com/JS/js_comparisons.asp




logical operators


&& and 5 == 5 && 4 != 6 TRUE

|| or 4 == 6 || 5 == 5 TRUE

! not !(5 == 4) TRUE


putting it all together


var a = 5;a += 3;a


var a = 5;a += 3;a // 8


var a = 2;var b = 5;a * b;


var a = 2;var b = 5;a * b; // 10


var a = 2;var b = 3;var c = a + b;var d = c * a;d


var a = 2;var b = 3;var c = a + b;var d = c * a;d // 10


var blue = 'blue';var red = 'red';var colors = [blue, red];colors


var blue = 'blue';var red = 'red';var colors = [blue, red];colors // ["blue","red"]


var a = 5;a = 6;a = 7;a -= 2;a


var a = 5;a = 6;a = 7;a -= 2;a // 5


var person = {name:'Peyton Manning'}person.name


var person = {name:'Peyton Manning'}person.name // "Peyton Manning"


var tv_shows = ['Wipeout', 'How I Met Your Mother', 'Big Bang Theory'];tv_shows[1] == 'How I Met Your Mother'


var tv_shows = ['Wipeout', 'How I Met Your Mother', 'Big Bang Theory'];tv_shows[1] == 'How I Met Your Mother' // true


var a = 5;var b = 4;var check = a == 5 && b == 3check


var a = 5;var b = 4;var check = a == 5 && b == 3check // false


var a = 5;var b = 4;var check = a == 3 || b > 3check


var a = 5;var b = 4;var check = a == 3 || b > 3check // true


var a = 5 - 1;a > 4


var a = 5 - 1;a > 4 // false


time to program

http://www.w3schools.com/JS/tryit.asp?filename=tryjs_intro

+ - * / % = == === != && || ! += -= /= *=




Technology

Variables Assignment And Operators