PHP is an open-source, server-side scripting language that was designed to be used with HTML. It can be object-oriented, and here is an overview of some of its features:

Data Types

Arrays

• To create a variable and assign it to an empty array, use the following format $newarr = array();
• To create a variable and assign it to an array, use: $newarr = array(1,2,3,4,5,6);

Associative Arrays

• Associative arrays are an object-indexed collection of objects, used when you need a key to retrieve data.

Constants

• The value of constants doesn’t change.
• Use quotes when defining the constant, define("CONST_VALUE", 10), once it’s been defined, don’t use the quotes when referencing it.
• You can’t redefine constants.

Booleans

• When PHP outputs ‘true’ into a string, it outputs 1. For ‘false,’ it outputs nothing.
• To check if a variable is a boolean, use is_bool();
• True and False can be written in uppercase or lowercase

Floats

• round(number1, number2) takes a number and how many significant digits you want there to be
• ceil(number) ceiling always rounds up
• floor(number) floor always rounds down
• is_float(number) to determine whether something is a float

Functions

• strtolower() changes a string to lower-case
• strtoupper() changes a string to upper-case
• ucfirst() changes first letter in string to upper-case
• ucwords() changes first letter of every word in the string to upper-case
• strleng() finds length of the string
• trim() eliminates white spaces
• strstr() find a string within a string (pass two parameters). Find a string within a string
• str_replace() takes three parameters – the string you’re looking for, what you want to replace it with, and the item we’re searching in

Integers

• abs(0 - 100) absolute value
• pow(3, 6) exponential (first number to the power of the second number)
• sqrt(25) square root
• fmod(17, 3) modulo
• rand() random
• rand(1,20) random (min, max)
• is_int(number) to determine whether something is an integer

Null and Empty

• Case insensitive
• is_null(); will test if an item is null
• An empty string, null, 0, 0.0, “0”, false, and an empty array, are all considered items that are empty

Strings

• Strings can include letters, text, html.
• Use double quotes or single quotes to denote strings
• Can do variable replacement inside of a string (but only when you use double quotes):

  <?php
  $phrase = "Hello World";
  ?>

  <?php
    echo "$phrase printed here<br>";
  ?>

• For in place substitution, use echo "{$phrase} Here<br>";

Debugging

• Use <?php phpinfo(); ?> to access more information about the configurations
• Missing semicolons are a common problem
• To turn on error reporting, in the php.ini file, display_errors = On and error_reporting = E_ALL, in PHP code, ini_set('display_errors', 'On'); and error_reporting(E_ALL);
• Turn off error reporting on live websites
• Use echo to make sure you’re getting the right values for variables
• print_r($array); to print readable array
• gettype($variable); to get variable type
• var_dump($variable); to get type and value
• get_defined_vars(); array of defined variables
• debug_backtrace(); show backtrace

Encoding

• For GET requests to pass a reserved character, you must encode them with urlencode($string) – letters, numbers, underscores, and dashes will be unchanged, but reserved characters become % + 2-digit hexidecimal, and spaces become +
• For rawurlencode, letters, numbers, and dashes are unchanged, reserved characters become % + 2-digit hexidecimal, and spaces become %20
• Use rawurlencode for the path, before the “?” section, and uses urlencode on the query string
• <, >, &, and ” are reserved characters in HTML
• HTML can be encoded with htmlspecialchars() and htmlentities()

Printing

To print items to the screen, use echo

Variables

• Start with a $ followed by a letter or underscore
• Can contain letters, numbers, underscores, or dashes and can’t contain spaces
• Case-sensitive