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Intro to Arrays in PHP

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• PHP Arrays
  • Array in PHP:

    An array in PHP is an associative array, a.k.a. a map A map is a data structure that associates (= maps): a key ----> a value

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  • Note:

    In CS377, we will only use the traditional array in PHP -- i.e., using only integer indices

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• Arrays that uses integer keys (= index)
  • Example: defining arrays that uses integer keys (= index)

    <?php $A[0] = 123; $A[1] = 3.14; $A[2] = "Hello"; for ( $i = 0; $i < 3; $i++ ) { print ( $A[$i] . "\n"); } print ("\n"); ?>

    Output:

    123 3.14 Hello

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  • Example Program: (Demo above code)                                                

    How to run the program:

    ssh -X holland php /home/cs377001/PHP/intro-PHP/array01.php

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• Number of elements in an array
  • count($A):

    count($A) = returns the number of (assigned) elements in the array $A

    Example:

    <?php $A[0] = 123; $A[1] = 3.14; $A[2] = "Hello"; for ( $i = 0; $i < count($A); $i++ ) { print ($A[$i] . "\n"); } print ("\n"); ?> Output: Number of elements = 3 123 3.14 Hello

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  • Example Program: (Demo above code)                                                

    How to run the program:

    ssh -X holland php /home/cs377001/PHP/intro-PHP/array02.php

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• PHP's special print function for structured variables
  • print_r( $var ) prints any type of variable in PHP

    Example:

    <?php $A[0] = 123; $A[1] = 3.14; $A[2] = "Hello"; print_r( $A ); print ("\n"); ?> php /home/cs377001/PHP/intro-PHP/array03.php Output: Array ( [0] => 123 [1] => 3.14 [2] => Hello )

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• Unexpected behavior of the assignment operation: = will makes a copy of an array
  • Important fact:

    The assignment operator with array variables will make a copy: $B = $A // will make a copy of array $A in $B

  • Example:

    $A[0] = 123; $A[1] = 3.14; $B = $A; // Make a COPY of array A in B $B[0] = "ABC123"; // $B[0] is changed, but $A[0] is unchanged Demo: php /home/cs377001/PHP/intro-PHP/array04.php Array A: Array ( [0] => 123 [1] => 3.14 ) Array B: Array ( [0] => 123 [1] => 3.14 ) ================================= Array A: Array ( [0] => 123 [1] => 3.14 ) Array B: Array ( [0] => ABC123 [1] => 3.14 ) Array A is not changed because B=A makes a COPY

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• Making an reference to an array
  • To make a reference to an array, use: = &

    Example:

    $A[0] = 123; $A[1] = 3.14; $B = & $A; // Make a reference of array A in B // B reference to the same array elements as A $B[0] = "ABC123"; // $B[0] is changed, but $A[0] is unchanged Demo: change /home/cs377001/PHP/intro-PHP/array04.php and then run php /home/cs377001/PHP/intro-PHP/array04.php Array A: Array ( [0] => 123 [1] => 3.14 ) Array B: Array ( [0] => 123 [1] => 3.14 ) ================================= Array A: Array ( [0] => ABC123 [1] => 3.14 ) Array B: Array ( [0] => ABC123 [1] => 3.14 ) Array A is changed because B=&A makes B refers to A

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• Associative array (arrays in PHP)
  • Associative array:

    Array index in PHP can be an arbitrary data type (we often use strings)

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  • Example:

    <?php $color["grass"] = "green"; $color["apple"] = "red"; $color["sky"] = "blue"; print_r( $color ); print ("\n"); ?> php /home/cs377001/PHP/intro-PHP/array05.php Array ( [grass] => green [apple] => red [sky] => blue )

    Comment:

    Associative arrays are also known as maps/dictionaries We don't need to use associative arrays in CS377