Zend Php 5 Certification - Arrays

Front 1

What are arrays?

Back 1

They are ordered collections of items, called elements. Each element has a value and is identified by a unique key.

Hint 1

P 47

Front 2

What are the two ways in which an array can be created?

Back 2

By calling the array() construct which can be passed a series of values, and optionally keys.

Examples:
$a = array(10,20,30); //keys are automatically assigned, starting at 0
$a = array("a' => 10, 'b' => 20, 'cee' => 30);
$a = array(5 => 1, 3 => 2, 1 => 3,); //"dangling comma has no effect on array
$a = array(); //empty array

The other method is to user the array operator.

Example:
$x[] = 10; //next highest numeric key assigned
$x['aa'] = 11;

Hint 2

P 47 - 48

Front 3

What are two functions PHP uses to output a variable's value (such as an array) recursively?

Back 3

var_dump($var1, $var2, etc...);

Will recusively print out the contents of a scaler and composite value(s), along with their data type.

print_r($var);
OR
$output = print_r($var, true);

Print out the contents of a composite or scaler variable, but NOT its type. Also, has option to return string to a variable.

Hint 3

P 48 - 49

Front 4

Arrays can be roughly divided into two categories: enumerative and associative. What does this mean?

Back 4

Enumerative: Indexed only using numerical values.

Associative: Associate an arbitrary key to every element (sometimes referred to as dictionaries).

Hint 4

P 49

Front 5

What will be the next numerical key for the following array:

$a = array("2" => 5);

Back 5

3. "2" can be converted to an integer since it is a traditional decimal representation. If it were "02" or "two", the next key would be 0.

Hint 5

P 49 - 50

Front 6

How would you create a multi-dimensional array in PHP?

Back 6

Example:

$array = array();

$array[] = array(
'foo',
'bar'
);
$array[] = array(
'baz',
'bat'
);

echo $array[0][1] . $array[1][0]; //print barbaz

Hint 6

P 50

Front 7

What does the list() construct does in the following code:

$info = array('coffee', 'brown', 'caffeine');
list($drink, $color, $power) = $info;

Back 7

$drink will = coffee
$color will = brown
$power will = caffeine

Useful when returning arrays from data rows in a database.

Example:

$result = mysql_query("SELECT id, name, salary FROM employees", $conn);
while (list($id, $name, $salary) = mysql_fetch_row($result)) {
echo " <tr>\n" .
" <td><a href=\"info.php?id=$id\">$name</a></td>\n" .
" <td>$salary</td>\n" .
" </tr>\n";
}

Hint 7

P. 50 - 51

Front 8

What does the addition operator do in the following example:

$a = array("a" => "apple", "b" => "banana");
$b = array("a" => "pear", "b" => "strawberry", "c" => "cherry");

$c = $a + $b; // Union of $a and $b
echo "Union of \$a and \$b: \n";
var_dump($c);

Back 8

Prints:

Union of $a and $b:
array(3) {
["a"]=>
string(5) "apple"
["b"]=>
string(6) "banana"
["c"]=>
string(6) "cherry"
}

Hint 8

P. 51 - 52
http://www.php.net/manual/en/language.operators.array.php

Front 9

When comparing arrays using the "==" and "===" operators, what is the difference?

Back 9

"==" will look at both the keys and the values of both arrays, return true if they exist both exist no matter what the order is.

"===" does the same as above, but the keys must be in the same order to return true

Hint 9

P. 52 - 53

Front 10

What does the count() function do for an array?

Back 10

Count() will return the number of elements in an array.

Example:
$a = array (1, 2, 3);
echo count($a); //Prints 3

Note, when count is used on a scaler value, it will always return 1. To determine if a variable is an array, use is_array() instead.

Hint 10

P. 53