PHP 2

MDST 3559: DataestheticsProf. Alvarado

02/17/2011

Business

• VPN?

Review

• PHP

– Variables, Data Types, Functions

– See Chapters 2 through 5 of Programming PHP

• Text

– Earlier we saw the text handled as a tree (CSS, jQuery)

– Tuesday we treated the text as an array, a simple linear sequence,

Overview

• Today we will go back over the basics of PHP – To provide a slightly different angle on the subject

– To help clarify some concepts for those new to programming

– To help clarify the “PHP way” for those with experience

• Then we will cover two new topics– Regular Expressions

– Creating your own functions

PHP as a language

• PHP is a programming langague (of course), but it has analogies to natural language as well

– There are parallels to the basic structures of human languages

• Which makes sense:

– Programming languages are designed to mediate between human and machine language

What are some elements of natural language?

Some Elements of Natural Language

• Words

• Meanings

• Sentences

– Something is said of something else

– Parts of speech: nouns, verbs, prepositions

– Heart of language as language, beyond mere signs

• Paragraphs

PHP has all of these things

Values are Meanings

• Values are pieces of data– Languages are all about doing things with data

• Data comes in types– Types include strings and numbers– Also Boolean values (true/false)

• Values are expressed literally and signified like so:“Hello, World!”5true

• These are the meanings of the language

Variables are Nouns

• Variables are words that can have meaning

$POTUS = “Obama”;

The President of the U.S. is Obama.

Like the difference between person and office

• They are like nouns that refer to things

– Things being values ...

• They are always prefixed by $ and are case sensitive

(Arrays)

• Arrays are admittedly weird

• But they can be thought of as words that stand for collections, e.g.

– The Pittsburgh Steelers

– The UVA student body

• These phrases imply a structure

– Albeit much more complicated than arrays

– But not much: consider rosters ...

Functions are Verbs

• Functions are like verbs$food = food_shop($me,$money,$humger_level)

• Like verbs, they may require arguments and imply a result– Verbs are action words

– Consider transitive versus intransitive

• They are not prefixed by $

• They are not case sensitive

• They are followed by parentheses

Functions

• Verbs have implicit arguments and effects

– Subjects, objects, indirect objects, are like arguments

– Intransitive verbs are like functions that don’t take an argument

• Or, it is implicit (the subject)

• Functions like verbs imply actions that produce effects

Person A: He ran for office.

Person B: And ... ?

Expressions• Expressions are like phrases that combine nouns and

verbs5(5 + 10) / 36“Tina” . “ is my cat”;file($url)$foo

• All expressions result in a value50.4166666 ...Tina is my cat[the array of the file][whatever $foo was last set to]

Statements

• Statements are like sentences. They combine one or more expressions.$my_cat = “Tina”;

$x = 2+2;

• They say something about somethingMy Cat is Tina.

$foois 2+2 (is 5)

The verb “to be” is an assignment operator ...

• They are always punctuated by a semi-colon

Operators

• Expressions and statements are built out of words by combining them with grammatical words, such as prepositions and conjunctions

Iam in the house.

I own a catanda dog.

• Operators are like the grammatical words

They don’t have meanings, they have functions

They don’t reference values (i.e. data), they do things with values

Operators

• ArithmeticAddition, subtraction, division, multiplication, etc.

• StringConcatenation

• AssignmentX is Y

• LogicalIs X Y?

Is X related to Y in some specified way?

Structures

• Structures, or control structures, are like stories or narrative patterns

• Built-in functions control conditions and iteration

– Repetition and branching

Conditions

• if / elseif/ else

if ($x == ‘foo’) {

// do something

} elseif ($x == ‘bar’) {

// do something else

} else {

// do something else

}

Iteration

• foreach()

• while()

Summary

• Values are like meanings

• Variables are like nouns

• Functions are like verbs

• Operators are like grammatical words

• These are combined to form expressions and statements

• Statements are structured in stories, or algorithms with control structures

Exercise

• Create directory for today

• Copy rex.php into it

• Let’s revisit the program and use control structures to format the text

– Use foreach() to loop through the file

– Use IF statements to grab what we want

– Format the text with tags

Two new functions

• preg_match($pattern, $string)

– Two arguments

• A regular expression pattern (between slashes “/.../”)

• A string to apply the expression to

• preg_replace($pattern,$replacement,$string)

– Three arguments

• A regular expression

• A something to replace the matched string with

• A string to apply the expression to

Regular Expressions

. = any character

+ = one or more

* = 0 or more

^ = beginning of the string

$ = end of the string

[A-Za-z] = character set of all letters

() = something to be replaced

Assignment

• Grab the Oedipux text

• Trim the leading and trailing HTML tags

• Reformat each line using either DIV or P elements

• Create an appropriate CSS stylesheet for the text