The PHP Scripting Language

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Chapter 2

• The PHP Scripting Language

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Topics

• PHP Basics
• Script structure
• Variables
• Supported Types
• Constants
• Expressions
• Type Conversions
• Condition and branch statements
• If, ifelse, switch
• Looping structures
• User-defined functions

3
Hello
Each block of code ends with a semi-colon.
Block of PHP code. Note that the code starts and
ends with a tag lt? ?gt and is embedded inside
the HTML. There are other places to put PHP as
we will see later.
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PHP Basics

• Three variations for tags
• lt?php ?gt
• This is the version we will use in the class
• lt? ?gt
• ltscript languagePHPgt lt/scriptgt
• Whitespace has no effect except to aid
  readability for the developer
• lt?php print Hello ?gt
• A script is a series of statements. Each
  statement is teminated with a semi-colon
• When the script is run, the entire script is
  replaced with the output of the code.

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Variables

• Identified by the dollar sign followed by the
  variable name.
• Unlike many other languages, you do not need to
  declare the variable before assigning it a value
• var 15
• They are case sensitive
• Variables are placeholders for data
• lt?php outputString Hello, world ?gt
• lt?php print outputString ?gt

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Comments

• // This is a one-line comment
• This is another one-line comment style
• / Use this for
• multi-line comments
• /

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Echo and Print

• Can be use the same way
• print Hello, world.
• echo Hello, world.
• The difference between the two is that echo can
  output more than one parameter separated by a
  comma
• // prints The answer is 42
• echo The answer is, 42

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String Literals

• String literals are the same as strings in PHP
• print This works the same as
• print this.
• Escaping
• The escape character is the backslash \

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Variable Substitution

• You can place a variable directly in a string but
  it is best to use curly braces for
  readability.
• number 45
• vehicle bus
• message This vehicle holds number
  people
• // This way is a little more difficult to read
• message2 This vehicle holds number people

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Character Encoding

• To correctly interpret characters, PHP needs to
  know the character encoding of the file. More
  simply, PHP needs to know what each 8-bit
  sequence that makes up the character means.
• PHP reads ISO-8859-1
• Equivalent to 7-bit ASCII for the first 127
  characters
• Instruct your browser to use this by adding the
  following line to your HTML ltheadgtlt/headgt
  section
• ltmeta http-equivContent-Type contenttext/html
  charsetiso-8859-1gt

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Types

• PHP has four scalar types
• Boolean, float, integer, and string
• Two compound types
• Array and object
• And NULL
• Used when a variable does not have a value

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Types

• Boolean are assigned either true or false
• var false
• test
• Integers are the same as counting numbers
• myInt 6
• Floats have a decimal place and can also be
  represented by exponential notation
• myFloat 6.6
• myFloat2 1.12e3 // equals 1120
• myFloat3 2e-2 // equals 0.02

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Constants

• Constants associate a name with a scalar value
• Unlike variables, they are not preceded by a
  character
• By convention constants are all uppercase
• define (NORMALTEMPERATURE, 96.8)
• print NORMALTEMPERATURE
• PHPs predefined constants use the first letter
  of the library name
• // This outputs 3.14159265358
• // and uses the letter M to represent the math
  library
• print M_PI

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Expressions, Operators, and Variable Assignment

• The value on the right side of the equals sign is
  called the expression
• // Simple example
• var 4 7
• // These all add one to var
• var var 1
• var 1
• var // This is the most common way to
  increment in PHP
• // These all subtract one from var
• var var 1
• var - 1
• var-- // again this notation is the most common
• //Double a value
• var var 2
• var 2

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String Expressions

• To concatenate a string you use the dot operator
• // Assign a string value to a variable
• strSnow snow day.
• var I want a . strSnow

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Operator Precedence

• PHP needs to decide which operator takes
  precedence.
• Here is the order
• Multiplication occur before subtraction and
  addition
• To avoid confusion, use parentheses to make you
  code clear.
• var 2 5 6
• // better to do it this way for clarity
• var 2 (5 6)

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Conditions and Branches If Else

• Without the braces the if statement only executes
  one line.
• if (grade gt 90)
• print A
• elseif (grade gt 80)
• print B
• else
• Your grade is a C or lower
• Multiple statements need the curly braces
• if (var gt 100)
• print The variable is greater than 100
• // We now need to reset the variable back to
  zero
• var 0

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Conditions and Branches switch Statements

• The switch statement can be used as an
  alternative to the if statement.
• switch(country)
• case USA
• echo ltpgtAmericanlt/pgt
• break
• case Belgium
• echo ltpgtFlemmishlt/pgt
• break