itm 352 - © port, kazmanvariables - 1 itm 352 data types, variables

ITM 352 - © Port, Kazman Variables - 1

ITM 352

Data types, Variables


AnnouncementsApache and NetBeans must be installed and

working on your laptop NOW During class:

Start NetBeans and create a new project “Lab1” Go to the Lab 1 assignment on Laulima. You may copy

and paste the exercises in to Word then back into the submission area or work directly on Laulima (just be sure to save a draft frequently)


AgendaLecture:

Outputting to the screen and console Data types Variables


Output in JS Use document.write() for simple output to the current

browser page document.write('hello'); // could use "hello"

To write to a particular location (i.e. page element) set its innerHTML attribute

<div id="place"></div> <script> document.getElementById("place").innerHTML='hello'; </script> Use console.log output to the JS console which is not

displayed on the browser page. It can only be seen through the browser tools or NetBeans Output (good for testing)console.log("hello");


Output in PHP Use echo for simple output

echo 'hello'; echo 'hello', ' goodbye'; echo ('hello');

print is virtually the same syntax print 'hello';

You can use () if you like echo('hello'); print('hello');

New line for console output (we don’t do much of this) echo "line1\nline2";

New line for HTML output echo 'line1<br>line2';


What is a Variable? A named location to store data

a container for data (like a box or bucket)

It can hold only one type of data at a time for example only integers, only floating point (real) numbers, or

only characters A variable with a scalar type holds one scalar value A variable with a compound type holds multiple scalar values,

BUT the variable still holds only a single (the compound type itself) value

Syntax for a variable is $<identifier> PHP Example: $name, $age JS Example: var name, var age Case sensitive!

$name $age

'Dan' 30.3


Assigning Values to Variables The assignment operator: "="

"sets" a value for a variable not the "is equal to" sign; not the same as in algebra

It means - "Assign the value of the expression on the right side to the variable on the left side."

Can have the variable on both sides of the equals sign:$count = 10;// initialize counter to ten

$count = $count - 1;// decrement counter

var count = 10;// initialize counter to ten

var count = count - 1;// decrement counter new value of count = 10 - 1 = 9


Creating Variables

A variable is declared the first time a value is set for it

A variable declaration associates a name with a storage location in memory and specifies the type of data it will store: $a = 1.1 ; // declares and sets a real number $a = true ; // declares and sets a boolean $a = 'Zip Zap' ; // declares and sets a string var a = 1.1 ; // declares and sets a real number var a = true; // declares and sets a boolean var a = 'Zip Zap' ; // declares and sets a string


Variable Names: Identifiers

Rules(these must be obeyed)

all identifiers must follow the same rules

must not start with a digit must contain only numbers,

letters, underscore (_) and some other special characters

names are case-sensitive (ThisName and thisName are two different variable names)

No spaces!

Good Programming Practice (these should be obeyed)

always use meaningful names from the problem domain (for example, eggsPerBasket instead of n, which is meaningless, or count, which is not meaningful enough)

start variable names with lower case capitalize interior words (use

eggsPerBasket instead of eggsperbasket)

use underscore (_) for spaces CAPITALIZE constants (i.e. variables

that do not change values)


Variable Default Values

Variables have default values $a = $a + 1; // $a=0 by default $s = $s."Fred"; // default $s='' var a = a + 1; // a=0 by default var s = s + "Fred"; // default s=""

IMPORTANT: It is best to not assume the default value is what you want. Always explicitly set the initial value of a variable!!!! e.g. $a = 0; $s = ""; $b = false;


Two Main Kinds of Data Types

Scalar the simplest types also called "primitive" or

"basic" types cannot decompose into

other types contain single values only Examples:

Integer Floating point (real) String Boolean

Compound also call class types more complex composed of other types

(primitive or class types) can contain multiple

values Examples:

Arrays Objects (more about these

in ITM353)


Which Ones to Know for Now - 1 integer

just whole numbers may be positive or negative no decimal point may use

Octal: 0755 // starts '0' Hex: 0xFF // starts '0x'

In PHP these are referred to as int boolean

only two values – true or false used for 'conditional' tests (e.g. if,

when) In PHP these are referred to as bool

floating point real numbers, both positive and

negative has a decimal point (fractional

part) two formats

number with decimal point, e.g. 514.061

e (or scientific, or floating-point) notation, e.g. 5.14061E2, which means 5.14061 x 102

In PHP these are referred to as double

null The 'nothing' type (more on

this later)


A string is a sequence of characters A very common data type

Names, passwords, addresses, histories, etc. Often used to represent complex data

Dates, phone numbers, SS numbers, formatted output A common data-interchange or data-sharing type

key-value pairs, XML, comma delimited data, logs PHP has a vast and powerful set of functions for working with strings.

JS not so much, but there are frameworks such as JQuery that do. Manipulation, searching, comparing, translation, etc. Check out php.net

Examples: “Mr. Smith”, ‘808-956-6948’, ‘21.7’, “1202 King St.”

Which Ones to Know for Now – 2.


NULL

Null is a special type that means "no value"It can be used to unset a variableIt is used as a place holder within

compound types (more on this later…) $a = NULL; // $a is “unset”, also can use unset($a)

var a = null; // var a; would set a as “undefined” not null

Do Exercise #1 in lab


Simple Expressions

Data types can be operated on (e.g. arithmetic, string operations) echo 1+2; echo 3*2; echo "Big" . " " . "Dude"; printf("5/3 is about %3d", 5/3);

Operators: +, -, ., *, /, %


Simple Expressions With VariablesVariables can be operated on (e.g.

arithmetic)

// add 1 to value in $a and set in $add$add = $a + 1;

// multiply value in $a by 2 and set in $mult $mult = $a * 2;

// concatenate string in $s with 'Fred' and// set in $str $str = $s . " Fred";


Printf() Use printf() for more complex formatted output printf('This prints 2 decimal places %.2f', 3.1415927);

This prints 2 decimal places 3.14

Printf() is a function whose first argument is a string that describes the desired format and the remaining arguments are the values to substitute into the type specifications (anything that starts with %)

Do Exercise #2,#3 (and bonus if you wish) in lab

itm 352 - © port, kazmanvariables - 1 itm 352 data types, variables

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