1. Kirkwood Center for Continuing Education
Introduction to PHP and MySQL
Kirkwood Center for Continuing Education
By Fred McClurg,
© Copyright 2016, Fred McClurg, All Rights Reserved.

2. Chapter Six Associative Arrays

3. 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;

4. Associative Array Element Initialization
Initialization via multiple statements:
<?php
$month['jan'] = 31;
$month['feb'] = 28;
$month['mar'] = 31;
$month['apr'] = 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.
What would be printed?

5. Hash Array Initialization Construct
Hash array initialization via a single statement:
<?php
$user = array( 'mluther' => 'Martin',
'bgraham' => 'Billy',
'dlmoody' => 'D.L.',
'jwesley' => 'John' );
foreach ( $user as $uname => $fname ) {
printf( "Username: %s  
First: %s<br>",
$uname, $fname ); }
?>
Note: The internal order of an associative array can not be guaranteed.
What would be printed?

6. Looping Associative Arrays
Chapter Six
Looping Associative Arrays

7. 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:
When the element value and the element key is needed.
When an operation is performed on every element.

8. The “foreach” Hash Array Syntax
foreach ( $array as
$key => $value ) {
statement;
... }

9. A “foreach” Hash Array Example
<?php
$color =
array( "red" => "#FF0000",
"green" => "#00FF00",
"blue" => "#0000FF" );
foreach ( $color as $key => $val ) {
printf( "\$color['%s']:
%s<br>", $key, $val ); }
?>
What would be printed?

10. 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:
In one statement, initialize an associative array to the zip code and city name. (ex: KW = 52404, NL = 52317, CV = 52241)
Use a foreach operator to print the zip code and the associated city name.

11. Student Solution 6.2 Using a Hash
<?php
$hash =
array( '52233' => 'Hiawatha',
'52302' => 'Marion',
'52314' => 'Mt Vernon',
'52328' => 'Robins',
'52333' => 'Solon' );
foreach ( $hash as $zip => $city ) {
printf( "City: %s  
Zip: %s<br>", $city, $zip ); }
?>

12. 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 ); }
?>
Question: How would you print out the months in order?
One Way To Do It (OWTDI):
// define an array with the months in order
$sorted = array( "jan", "feb", "mar", "apr", "may", "jun", "jul", "aug", "sep", "oct", "nov", "dec" );
...
foreach ( $sorted as $name ) {
printf( "%s has %d days<br>", $name, $month[$name] ); }

13. 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 before being incremented.

14. 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 ); }
?>

15. to be continued ...