Friday 15 March 2013

PHP Array and Loop

PHP Array

An array stores multiple values in one single variable.
A variable is a storage area holding a number or text. The problem is, a
variable will hold only one value.
An array is a special variable, which can store multiple values in one
single variable.

If you have a list of items (a list of car names, for example), storing the
cars in single variables could look like this:

$cars1="Saab";
$cars2="Volvo";
$cars3="BMW";

However, what if you want to loop through the cars and find a specific
one? And what if you had not 3 cars, but 300?
The best solution here is to use an array!

An array can hold all your variable values under a single name. And you
can access the values by referring to the array name.
Each element in the array has its own index so that it can be easily
accessed.

In PHP, there are three kind of arrays:

•Numeric array - An array with a numeric index

•Associative array - An array where each ID key is associated with
a value

•Multidimensional array - An array containing one or more arrays

Numeric Arrays


A numeric array stores each array element with a numeric index.
There are two methods to create a numeric array.

1. In the following example the index are automatically assigned (the
index starts at 0):

$cars=array("Saab","Volvo","BMW","Toyota");

2. In the following example we assign the index manually:

$cars[0]="Saab";
$cars[1]="Volvo";
$cars[2]="BMW";
$cars[3]="Toyota";

Example

In the following example you access the variable values by referring to
the array name and index:

<?php
$cars[0]="Saab";
$cars[1]="Volvo";
$cars[2]="BMW";
$cars[3]="Toyota";
echo $cars[0] . " and " . $cars[1] . " are Swedish cars.";
?>

The code above will output:
Saab and Volvo are Swedish cars.



Associative Arrays


In associative array, each ID key is associated with a value.
When storing data about specific named values, a numerical array is not
always the best way to do it.
With associative arrays we can use the values as keys and assign values
to them.

Example 1
In this example we use an array to assign ages to the different persons:

$ages = array("Peter"=>32, "Quagmire"=>30, "Joe"=>34);

Example 2
This example is the same as example 1, but shows a different way of
creating the array:

$ages['Peter'] = "32";
$ages['Quagmire'] = "30";
$ages['Joe'] = "34";

The ID keys can be used in a script:
<?php
$ages['Peter'] = "32";
$ages['Quagmire'] = "30";
$ages['Joe'] = "34";

echo "Peter is " . $ages['Peter'] . " years old.";
?>

The code above will output:
Peter is 32 years old.

PHP Loops


Often when you write code, you want the same block of code to run over
and over again in a row. Instead of adding several almost equal lines in a
script we can use loops to perform a task like this.

In PHP, we have the following looping statements:

•while - loops through a block of code while a specified condition is
true

•do...while - loops through a block of code once, and then repeats
the loop as long as a specified condition is true

•for - loops through a block of code a specified number of times

•foreach - loops through a block of code for each element in an
array

The while Loop


The while loop executes a block of code while a condition is true.
Syntax

while (condition)
{
code to be executed;
}

Example
The example below defines a loop that starts with i=1. The loop will
continue to run as long as i is less than, or equal to 5. i will increase by 1
each time the loop runs:

<html>
<body>

<?php
$i=1;
while($i<=5)
{
echo "The number is " . $i . "<br />";
$i++;
}
?>

</body>
</html>

Output:
The
The
The
The
The

number
number
number
number
number

is
is
is
is
is

1
2
3
4
5

The do...while Statement


The do...while statement will always execute the block of code once, it
will then check the condition, and repeat the loop while the condition is
true.

Syntax
do

{
code to be executed;
}
while (condition);

Example
The example below defines a loop that starts with i=1. It will then
increment i with 1, and write some output. Then the condition is checked,
and the loop will continue to run as long as i is less than, or equal to 5:

<html>
<body>

<?php
$i=1;
do
{
$i++;
echo "The number is " . $i . "<br />";
}
while ($i<=5);
?>

</body>
</html>

Output:
number
number
number
number
number

The
The
The
The
The

is
is
is
is
is

2
3
4
5
6

The for Loop


The for loop is used when you know in advance how many times the
script should run.
Syntax

for (init; condition; increment)
{
code to be executed;
}

Parameters:

•init: Mostly used to set a counter (but can be any code to be
executed once at the beginning of the loop)

•condition: Evaluated for each loop iteration. If it evaluates to TRUE,
the loop continues. If it evaluates to FALSE, the loop ends.

•increment: Mostly used to increment a counter (but can be any
code to be executed at the end of the loop)

Note: Each of the parameters above can be empty, or have multiple
expressions (separated by commas).

Example
The example below defines a loop that starts with i=1. The loop will
continue to run as long as i is less than, or equal to 5. i will increase by 1
each time the loop runs:

<html>
<body>

<?php
for ($i=1; $i<=5; $i++)
{
echo "The number is " . $i . "<br />";
}
?>

</body>
</html>

Output:

number
number
number
number
number

The
The
The
The
The

is
is
is
is
is

1
2
3
4
5

The foreach Loop


The foreach loop is used to loop through arrays.

Syntax
foreach ($array as $value)
{
code to be executed;
}

For every loop iteration, the value of the current array element is
assigned to $value (and the array pointer is moved by one) - so on the
next loop iteration, you'll be looking at the next array value.

Example

The following example demonstrates a loop that will print the values of
the given array:

<html>
<body>

<?php
$x=array("one","two","three");
foreach ($x as $value)
{
echo $value . "<br />";
}
?>

</body>
</html>

Output:

one
two
three

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