Introduction to
PHP and MySQL
Kirkwood Center for
Continuing Education
By Fred McClurg, frmcclurg@gmail.com
© Copyright 2010 All Rights Reserved.
1
Chapter Six
Associative Arrays
http://webcert.kirkwood.edu/~fmcclurg/co
urses/php/slides/chapter06.associative.ppt
2
Associative Array (aka Hash)
Description: An associative array uses
an unique string called a “key” as the
index to each element.
Syntax:
$var['key'] = $value;
3
Associative Array Element Initialization
Initialization via multiple statements:
<?php
$month['jan']
$month['feb']
$month['mar']
$month['apr']
...
=
=
=
=
31;
28;
31;
30;
foreach ( $month as $name => $days )
{
printf( "%s has %d days<br />",
$name, $days );
}
?>
Note: The internal order of an associative array can not be guaranteed. 4
Hash Array Initialization Construct
Hash array initialization via a single statement:
<?php
$user = array( 'mluther'
'bgraham'
'dlmoody'
'jwesley'
=>
=>
=>
=>
'Martin',
'Billy',
'D.L.',
'John' );
foreach ( $user as $uname => $fname )
{
printf( "Username: %s &nbsp;
First: %s<br />",
$uname, $fname );
}
?>
Note: The internal order of an associative array can not be guaranteed.
5
Chapter Six
Looping Associative Arrays
6
Looping Hash Arrays via “foreach”
Description: The “foreach” construct can
also be used to iterate through an
associative array to obtain the key and
value of each element.
Preferred Usage:
1. When the element value and the
element key is needed.
2. When an operation is performed on
every element.
7
The “foreach” Hash Array Syntax
Syntax:
foreach ( $array as
$key => $value )
{
statement;
...
}
8
A “foreach” Hash Array Example
Example:
<?php
$color =
array( "red" => "#FF0000",
"green" => "#00FF00",
"blue" => "#0000FF" );
foreach ( $color as $key => $val )
{
printf( "\$color['%s']:
%s<br />", $key, $val );
}
?>
9
Student Exercise 6.2 Using a Hash
Problem: Write a PHP program that creates an
associative array with the zip code as the
key and the city name as the value.
Requirements:
1. In one statement, initialize an associative
array to the zip code and city name. (ex:
KW = 52404, NL = 52317, CV = 52241)
2. Use a foreach operator to print the zip
code and the associated city name.
10
Student Solution 6.2 Using a Hash
<?php
$hash =
array( '52233'
'52302'
'52314'
'52328'
'52333'
=>
=>
=>
=>
=>
'Hiawatha',
'Marion',
'Mt Vernon',
'Robins',
'Solon' );
foreach ( $hash as $zip => $city )
{
printf( "City: %s &nbsp;
Zip: %s<br />", $city, $zip );
}
?>
11
Using a Variable as Hash Key
<?php
$year = 1960; // leap year
$thirty = array( 'sep', 'apr', 'jun', 'nov' );
$thirtyOne = array( 'jan', 'mar', 'may', 'jul',
'aug', 'oct', 'dec' );
foreach( $thirty as $name )
$month[$name] = 30; // initialize 30 day months
foreach( $thirtyOne as $name )
$month[$name] = 31; // initialize 31 day months
// $month['feb'] = isLeapYear( $year ) ? 29 : 28;
$month['feb'] = 29; // initialize leap year month
// how would you print out months in order?
foreach ( $month as $name => $days )
{
printf( "%s has %d days<br />",
$name, $days );
}
?>
12
Using a Hash to Create an Unique List
Description: An associative array can be used to reduce a list to unique values.
<?php
$cartoon =
array( 'Fred', 'Barney', 'Fred', 'Wilma',
'Fred', 'Pebbles', 'Fred', 'Dino' );
foreach ( $cartoon as $name )
$unique[$name]++; // count occurrences
foreach ( $unique as $name => $occur )
printf( "Actor %s occurred %d times<br />",
$name, $occur );
?>
Note: All uninitialized variables have a value of NULL that are promoted to zero 13
before being incremented.
Looping Hashes via “each” in a “while”
Example:
<?php
$color = array( "red" => "#FF0000",
"green" => "#00FF00",
"blue" => "#0000FF" );
while (list($key, $val) = each($color))
{
printf( "\$color['%s']: %s<br />",
$key, $val );
}
?>
14
to be continued ...
http://webcert.kirkwood.edu/~fmcclurg/cour
ses/php/slides/chapter06c.multidimential.ppt