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10 Cards in this Set
- Front
- Back
- 3rd side (hint)
What are arrays?
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They are ordered collections of items, called elements. Each element has a value and is identified by a unique key.
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P 47
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What are the two ways in which an array can be created?
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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 $x['aa'] = 11; |
P 47 - 48
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What are two functions PHP uses to output a variable's value (such as an array) recursively?
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var_dump($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. |
P 48 - 49
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Arrays can be roughly divided into two categories: enumerative and associative. What does this mean?
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Enumerative: Indexed only using numerical values.
Associative: Associate an arbitrary key to every element (sometimes referred to as dictionaries). |
P 49
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What will be the next numerical key for the following array:
$a = array("2" => 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.
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P 49 - 50
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How would you create a multi-dimensional array in PHP?
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Example:
$array = array(); $array[] = array( 'foo', 'bar' ); $array[] = array( 'baz', 'bat' ); echo $array[0][1] . $array[1][0]; //print barbaz |
P 50
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What does the list() construct does in the following code:
$info = array('coffee', 'brown', 'caffeine'); list($drink, $color, $power) = $info; |
$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"; } |
P. 50 - 51
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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); |
Prints:
Union of $a and $b: array(3) { ["a"]=> string(5) "apple" ["b"]=> string(6) "banana" ["c"]=> string(6) "cherry" } |
P. 51 - 52
http://www.php.net/manual/en/language.operators.array.php |
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When comparing arrays using the "==" and "===" operators, what is the difference?
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"==" 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 |
P. 52 - 53
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What does the count() function do for an array?
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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. |
P. 53
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