PHP looping...

Looping

Very often when you write code, you want the same block of code to run a number of times. You can use looping statements in your code to perform this.

In PHP we have the following looping statements:

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

The while statement will execute a block of code if and as long as a condition is true.
Syntax

while (condition)
code to be executed;

Example

The following example demonstrates a loop that will continue to run as long as the variable i is less than, or equal to 5. i will increase by 1 each time the loop runs:




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





The do...while Statement

The do...while statement will execute a block of code at least once - it then will repeat the loop as long as a condition is true.
Syntax

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

Example

The following example will increment the value of i at least once, and it will continue incrementing the variable i as long as it has a value of less than 5:




$i=0;
do
{
$i++;
echo "The number is " . $i . "
";
}
while ($i<5);
?>





The for Statement

The for statement is used when you know how many times you want to execute a statement or a list of statements.
Syntax

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

Note: The for statement has three parameters. The first parameter initializes variables, the second parameter holds the condition, and the third parameter contains the increments required to implement the loop. If more than one variable is included in the initialization or the increment parameter, they should be separated by commas. The condition must evaluate to true or false.
Example

The following example prints the text "Hello World!" five times:




for ($i=1; $i<=5; $i++)
{
echo "Hello World!
";
}
?>





The foreach Statement

The foreach statement is used to loop through arrays.

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

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

Example

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




$arr=array("one", "two", "three");

foreach ($arr as $value)
{
echo "Value: " . $value . "
";
}
?>

PHP arrays.......

What is an array?

When working with PHP, sooner or later, you might want to create many similar variables.

Instead of having many similar variables, you can store the data as elements in an array.

Each element in the array has its own ID so that it can be easily accessed.

There are three different kind of arrays:

* Numeric array - An array with a numeric ID key
* 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 element with a numeric ID key.

There are different ways to create a numeric array.
Example 1

In this example the ID key is automatically assigned:

$names = array("Peter","Quagmire","Joe");

Example 2

In this example we assign the ID key manually:

$names[0] = "Peter";
$names[1] = "Quagmire";
$names[2] = "Joe";

The ID keys can be used in a script:


$names[0] = "Peter";
$names[1] = "Quagmire";
$names[2] = "Joe";

echo $names[1] . " and " . $names[2] .
" are ". $names[0] . "'s neighbors";
?>

The code above will output:

Quagmire and Joe are Peter's neighbors


Associative Arrays

An 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:


$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.


Multidimensional Arrays

In a multidimensional array, each element in the main array can also be an array. And each element in the sub-array can be an array, and so on.
Example

In this example we create a multidimensional array, with automatically assigned ID keys:

$families = array
(
"Griffin"=>array
(
"Peter",
"Lois",
"Megan"
),
"Quagmire"=>array
(
"Glenn"
),
"Brown"=>array
(
"Cleveland",
"Loretta",
"Junior"
)
);

The array above would look like this if written to the output:

Array
(
[Griffin] => Array
(
[0] => Peter
[1] => Lois
[2] => Megan
)
[Quagmire] => Array
(
[0] => Glenn
)
[Brown] => Array
(
[0] => Cleveland
[1] => Loretta
[2] => Junior
)
)

Example 2

Lets try displaying a single value from the array above:

echo "Is " . $families['Griffin'][2] .
" a part of the Griffin family?";

The code above will output:

Is Megan a part of the Griffin family?

Going on through php...

Conditional Statements

Very often when you write code, you want to perform different actions for different decisions.

You can use conditional statements in your code to do this.

* if...else statement - use this statement if you want to execute a set of code when a condition is true and another if the condition is not true
* elseif statement - is used with the if...else statement to execute a set of code if one of several condition are true

The If...Else Statement

If you want to execute some code if a condition is true and another code if a condition is false, use the if....else statement.
Syntax

if (condition)
code to be executed if condition is true;
else
code to be executed if condition is false;

Example

The following example will output "Have a nice weekend!" if the current day is Friday, otherwise it will output "Have a nice day!":




$d=date("D");
if ($d=="Fri")
echo "Have a nice weekend!";
else
echo "Have a nice day!";
?>




If more than one line should be executed if a condition is true/false, the lines should be enclosed within curly braces:




$d=date("D");
if ($d=="Fri")
{
echo "Hello!
";
echo "Have a nice weekend!";
echo "See you on Monday!";
}
?>





The ElseIf Statement

If you want to execute some code if one of several conditions are true use the elseif statement
Syntax

if (condition)
code to be executed if condition is true;
elseif (condition)
code to be executed if condition is true;
else
code to be executed if condition is false;

Example

The following example will output "Have a nice weekend!" if the current day is Friday, and "Have a nice Sunday!" if the current day is Sunday. Otherwise it will output "Have a nice day!":




$d=date("D");
if ($d=="Fri")
echo "Have a nice weekend!";
elseif ($d=="Sun")
echo "Have a nice Sunday!";
else
echo "Have a nice day!";
?>