PHP

1
PHP

• SI 539
• Fall 2004
• Prof. Sandra Bartlett

2
What is PHP?

• PHP Hypertext Pre-processor (formerly known as
  Personal Home Page)
• Widely used
• General-purpose
• Server-side scripting language
• Especially suited for Web development
• Can be embedded in HTML

3
Advantages

• Access a remote database
• Script is invisible to the end user, unlike
  JavaScript (JavaScript) (PHP)
• Browser needs no plug-in
• Parts can be implemented in compiled languages
  like C/C
• Thin client

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Disadvantages

• Web server does more work has to create the
  page as well as send it
• If user saves the page, it looses its
  functionality
• Pages may not load properly when you click the
  reload button
• A bookmarked page may not work

5
What is a Programming Language

• Makes it easier for people to tell the computer
  what to do
• Translates English-like text into 0s and 1s
  that the computer can understand
• Types
• Compiled translate before running
• Interpreted translate and run at the same time
• Both

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What kind is PHP?

• Interpreted
• Web server does the work (with JavaScript, the
  browser does the work)
• Looks a lot like C, C, Java, JavaScript,
  Fortran, Pascal, etc.
• What you need to learn
• Vocabulary and syntax
• Built-in functions

7
Comments

• Help you and others read the source
• Fix bugs
• Make changes
• Add new stuff
• Types
• // single line comment
• / block comment
• cant be nested /

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Variables

• Make you pages dynamic, not static
• Hold information to use later
• Only need to change the information once and it
  will be correct in all the places you use it

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Variable Names

• Case sensitive
• Must be meaningful
• Start with , then a letter, then any number of
  letters, digits, _, but not space
• Examples
• fred fred2
• fred_fred fredFred (course style)

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Creating Variables

• var fred
• fred now exists
• fred has no value it is empty
• mary hi
• mary now exists
• mary holds the string hi

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Assign value

• Tell computer what you want it to remember
• is symbol for assignment
• Put variable name on left of Put value on the
  right and a at the end
• Examples
• price 5
• t2 Doctor

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Kinds of Values (data types)

• Numbers
• Signed integers (-3 0 456344 etc.)
• Floats (1.234 1.2e3 7E-10 )
• Booleans
• TRUE FALSE (not case sensitive)
• Also can be treated as false 0 0 0.0 NULL
• Also can be treated as true 1 -1 .3 fred
• Strings

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Floats

• Size is platform dependent
• the biggest and smallest values can be different
  on different machines
• Precision
• Sometimes floating point math comes out with the
  wrong answer
• Not all floating point numbers can be exactly
  represented in the computer
• 1/3
• Round off error

14
Strings

• Characters inside double quotes ( ) or single
  quotes ( )
• Characters are all the things you can type on a
  keyboard
• A b c etc.
• 1 2 3 etc.
• Space, tab, return, etc.
• F1 delete etc.
• Foreign language characters etc.

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Assigning Values

• fred 3.5
• fred me!
• fred -3.14159
• fred TRUE
• PHP variable are not typed any one variable can
  hold any thing.

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Which Quotes For Strings?

• fred 44
• single quotes all the characters in the
  string are part of the string
• this is fred
• this is fred
• double quotes
• Understands escape characters
• Expands variables

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Escape Characters

• Start with back slash \
• \n newline
• \t tab
• \ (not part of a variable name)
• \ double quote
• \\ \
• \ single quote (inside single quotes only)

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Expanding Variables

• fred 44
• single quotes all the characters in the
  string are part of the string
• this is fred
• this is fred
• double quotes variables are expanded
• this is fred
• this is 44

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Expansion is GREEDY!!

• Takes as many letters as it can for the variable
  name
• food chocolate'
• We ate foods. -gt We ate foods.
• We ate foods. -gt no such variable
• We ate foods. -gt We ate chocolates.

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Implicit Type Conversion

• foo 4"  // foo is string
• foo foo 2  // foo is now an integer (6)
• foo foo 1.3  // foo is now a float (3.3)
• foo 5 "10 Little Piggies" // foo is
  integer (15)
• foo foo "10 Small Pigs"  // foo is
  integer (25)

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Explicit Type Conversion

• foo 4"  // foo is string
• foo (int) foo  // foo is now an integer (4)
• foo (bool) foo// foo is now boolean
• foo (string) foo // foo is now 1

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How to Print

• echo( ) - language construct () optional
• Just does the printing
• Can print multiple strings (dont use () for
  this)
• print() - function () optional
• Returns 1 always
• Can only print one string

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Print Example

• print()ing in PHP

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How Can the Server Tell PHP From HTML?

• TAGS!!!! ?
• For the course and XHTML
• lt?php ?gt
• Short tags, not always available
• lt? ?gt
• Also works (asp style)
• ltscript language"php"gt lt/scriptgt

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Example

• Mixing PHP and HTML

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For Lab

• rand(int min, int max)
• Built-in function
• Returns a random integer between min and max,
  inclusive
• fred rand(5, 10)
• fred will hold an integer greater than or equal
  to 5 and less than or equal to 10
• 5 6 7 8 9 10