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Data types in PHP

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• PHP Variable Types
  • PHP supports 8 primitive types.

    Four scalar types: boolean integer float (C's double)           string Two compound types: array object (C's struct)           Two special types: resource (special variable, holding a reference to an external resource) NULL

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• Denoting a variable in PHP
  • Syntax to denote a variable in PHP:

    $variableName // Simple variable $variableName[index] // Array variable

    I.e.: a variable must be preceeded by a dollar sign $ !!!

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  • Syntax of a variable name: ( = like an identifier)

    Starts with letter or underscore followed by zero or more letter, digit or underscore A variable name is case-sensitive

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  • Examples:

    $a $A // Different variable name !!

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• "Defining" a variable (of a given data type)
  • Fact:

    You do not need to define variables in PHP (nor in most scripting languages)

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  • How to "define" a variable in PHP:

    A variable is define when you assign a value to the variable

    Example:

    <?php // variable x does not exist yet $x = 1; // NOW variable x is defined ?>

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• Accessing an undefined variable
  • Using (= accessing) an undefined variable

    PHP will print an error message if you use (= access) a variable before it was created.

    Example:

    <?php /* ----------------------------------- variable x does not exist yet ----------------------------------- */ print "1. x = " . $x . "\n"; // Error $x = 1; // NOW variable x is defined print "2. x = " . $x . "\n"; // No error ?>

    Output:

    PHP Notice: Undefined variable: x in .../undef-var.php on line 6 1. x = 2. x = 1

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  • Example Program: (Demo above code)                                                

    How to run the program:

    ssh -X yourID@holland php /home/cs377001/PHP/intro-PHP/undef-var.php