Arrays in PHP: Index Values and Associative Arrays

PHP Arrays CSC 242 Professor John Carelli Kutztown University Computer Science Department

Arrays in PHP PHP supports arrays that consist of an indexed list of elements Two types are supported: Arrays with numerical index values Arrays with arbitrary index values (typically strings) Also referred to as associate arrays Professor John Carelli Kutztown University Computer Science Department

Arrays with Integer Keys Integer index values are placed in square backets following the array base name Using explicit indices: <?php $a[0] = "one"; $a[1] = "two"; $a[2] = "three"; ?> Missing index value creates a new index at the end (i.e., push operation): <?php $a[] = "one"; $a[] = "two"; $a[] = "three"; ?> Professor John Carelli Kutztown University Computer Science Department

Associative Array String index values are placed in square backets following the array base name (in quotes) Resulting in a mapping of key / value pairs <?php $b['one'] = 1; $b['two'] = 2; $b['three'] = 3; ?> If multiple elements are declared with the same key, then only the last value is retained (previous value is overwritten) Professor John Carelli Kutztown University Computer Science Department

More on Keys Associative arrays a string containing a valid integer will be cast to an integer floats and bools get cast to integers (floats get truncated) Null value gets cast to an empty string Arrays and objects cannot be used as keys Professor John Carelli Kutztown University Computer Science Department

Printing Arrays print_r() print an entire array: print_r($MyArray); Outputs a human-readable representation When used in HTML, enclose it in <pre> tags to make it pretty (otherwise, the whitespace in the output will get collapsed) An array element can be used as a variable in a string interpolation echo "$var[0]"; however, Professor John Carelli Kutztown University Computer Science Department

Printing Arrays with string keys If the key is not an integer, the element must be enclosed in curly braces, or an interpolation error will result. Correct: echo "${var['key']}"; Incorrect, without curly braces: php > echo "$var['key']"; PHP Parse error: syntax error, unexpected '' (T_ENCAPSED_AND_WHITESPACE), expecting '-' or identifier (T_STRING) or variable (T_VARIABLE) or number (T_NUM_STRING) in php shell code on line 1 Professor John Carelli Kutztown University Computer Science Department

array keyword Define an array with the array keyword Numerical index: $a = array("one", "two", "three"); Associative array: $b = array( 'one' => 1, 'two' => 2, 'three' => 3); Professor John Carelli Kutztown University Computer Science Department

foreach loop Theforeach loop can be used to iterate through the values of an array Arrays with integer keys: foreach($a as $element) { echo "$element"; } Associative arrays: foreach($b as $key => $value) { echo "$key: $value"; } Source: Dylan Schwesinger Kutztown University Computer Science Department

Multidimensional Arrays The value of a key can be an array $tic_tac_toe = array( array('X', ' ', 'O'), array('O', 'O', 'X'), array('X', 'O', ' ') ); Source: Dylan Schwesinger Kutztown University Computer Science Department

Useful built-in Array Functions is_array will return true if a variable is an array count will return the number of elements in an array sort performs an in-place sorting of array elements explode converts a string into an array implode converts an array into a string array_keys returns an array containing the keys of an array array_values returns an array containing the elements of an array unset removes an element from an array Professor John Carelli Kutztown University Computer Science Department

PHP Examples Arrays & Files firstArray.php arrayExamples.php sortArrays.php Professor John Carelli Kutztown University Computer Science Department

Superglobals Predefined variables that are provided by the PHP environment $_GET: variables passed to the current script via the HTTP GET method $_POST: variables passed to the current script via the HTTP POST method $_COOKIE: variables passed to the current script via HTTP cookies $_SESSION: session variables available to the current script Professor John Carelli Kutztown University Computer Science Department