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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 data structure that stores one or more values in a single value.

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 array:

A numeric array stores each array element with a numeric index.

Imagine that you own a car dealer and you want to store the names of all your cars in a PHP variable. How would you go about this?

It wouldn’t make much sense to have to store each name in its own variable. Instead, it would be nice to store all the car names inside of a single variable. This can be done, and we show you how below.

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

In the above example we made use of the key / value structure of an array. The keys were the numbers we specified in the array and the values were the names of the cars. Each key of an array represents a value that we can manipulate and reference. The general form for setting the key of an array equal to a value is:

* $array[key] = value;

Associative array:

An associative array, each ID key is associated with a value.

If you wanted to store the age of your employees in an array, a numerically indexed array would not be the best choice. Instead, we could use the employees names as the keys in our associative array, and the value would be their age.

$ages['John'] = “35″;
$ages['Sally'] = “31″;
$ages['Jasmine'] = “32″;

echo “John is ” . $ages['John'] . “<br />”;
echo “Sally is ” . $ages['Sally'] . “<br />”;
echo “Jasmine ” . $ages['Jasmine'] ;

The code above will output:

John is 35
Sally is 31
Jasmine is 32

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.

Switch Statement are used to perform different actions based on different conditions. Switch statements are just like if..else conditional statements where a block of code is executed if the condition is true.

Example:

<?php
switch ($x)
{
case 1:
echo “Number 1″;
break;
case 2:
echo “Number 2″;
break;
case 3:
echo “Number 3″;
break;
default:
echo “Hello”;
} ?>

The default case:

What if no number between 1 and 3 are entered? In that case, the default statement in switch code will be executed. In the example above we set the string “Hello”.

The code will executed the default code block since we don’t enter the number between 1 and 3  is not part of our switch statement cases. The code will output “Hello”.

The Break Statement:

The break statement in PHP switch code prevents the code from executing other cases in the switch statement. When a case is matched in a switch statement, the break statement basically stops the code execution. If the break statement is not there, then each case is executed.

Think about the decisions you make before you go to bed. If you have homework to do the next day, then you will have to finish before go to bed. Otherwise, you will read book or watch TV as you like!

In programming, whenever you want to make a decision given that something is true and be sure that you take the appropriate action, you are using an if..else relationship.

In PHP we have the following conditional statements:

• if statement – use this statement to execute some code only if a specified condition is true
• if…else statement – use this statement to execute some code if a condition is true and another code if the condition is false
• if…elseif….else statement – use this statement to select one of several blocks of code to be executed
• switch statement – use this statement to select one of many blocks of code to be executed

The if Statement Example:

$my_name = “vn4000″;

if ( $my_name == “vn4000″ ) {
echo “Hello vn4000!<br />”;
}
echo “Web programming!”;

The if…else Statement Example:

<?php
$my_name = “vn4000″;
if ($my_name == “vn4000″)
echo “Have a nice day, vn4000!”;
else
echo “Have a nice day everybody!”;
?>

Below are the operators used in PHP

Arithmetic Operators

Assignment Operators

Comparison Operators

Logical Operators

You can store the following simple types of data in PHP variables:

1. Integer: A whole number (no fractions), such as –43, 0, 1, 27, or 5438. The range of integers that is allowed varies, depending on your operating system, but in general, you can usually use any number from –2 billion up to +2 billion.
2. Floating point number: A number (usually not a whole number) that includes decimal places, such as 5.24 or 123.456789. This is often called a real number or a float.
3. Character string: A series of single characters, such as hello. There is no practical limit on the length of a string.
4. Boolean: A TRUE or FALSE value.

Assigning data types

You don’t need to tell PHP which data type is in a variable. PHP evaluates the data when you assign it to the variable and then stores it as the appropriate type.

Type casting

The data type of variables are automatically determined by the value placed in variable

$a=1  / / $ a is an integer
$a=1.2 / / double
$a=”1″ / / string

Type casting allows you to change the data type of the variable

$a=11.2/ / $ a is a real type
$a=(int)$a / / now $ a is integer, value = 11
$a= (double) $a / / now $ a return to style = 11.0
$b= (string)$a / / $ b is a string value = “11″

The value in the variable on the right side of the equal sign is stored in the variable on the left side as the specified type.

Be careful when doing type casts. Sometimes you can get unexpected results. For example, when you cast a float into an integer, it loses its decimal places. PHP rounds the float toward 0. For example, if $number = 2.7 and you cast it into an integer — $newnumber = (int) $number — $newnumber will equal 2.

The comments section is useful in your program. The PHP comment syntax always begins with a special character sequence and all text that appears between the start of the comment and the end will be ignored, but a programmer would never ignore them.

• Single Line Comment: Use // for single line comments

echo “Hello World!”; // This will print out Hello World!

• Multiple Line Comment: begins with ” /* ” and ends with ” */ “.

<?php
/* the multi-line PHP comment can be used to
comment out large blocks of code */
echo “Hello World!”;
?>

Special Characters:

You can’t simply place the double quote within a set of double quotes because it will cause an error in PHP. To overcome this dilemma, a method called an “escape” is used to allow developers to store this special character along with others in strings.

For example the following code will print My name is “vn4000.net” (inclued double quote) to the screen:

<?php
echo (“My name is : \” vn4000.net\ “”);
?>

Below is a table of other special characters that require a backslash:

<?php
$str = “Hello World!”;
echo $str;
?>

The output of the code above will be:

Hello World!

Output is simple string only. However, it is important that we use proper HTML syntax. Try as below:

<?php
echo “<h3>Hello World!</h3>”;
?>

Ok, one more try:

<?php
$str = “Hello World!”;
echo “We are learning PHP, $str“;
?>

Note:

1. Don’t use quotes inside your string
2. Escape your quotes that are within the string with a backslash. To escape a quote just place a backslash directly before the quotation mark, i.e. \”
3. Use single quotes (apostrophes) for quotes inside your string.

Example:
<?php
// This won’t work because of the quotes around special
echo “John said that He’ll be back”;
// Outputs: John said: “I’ll be back”
echo ‘John said: “I\’ll be back”‘;

?>

Suppose you want to know something about the level of PHP we are discussing. We do the “telling” like this:

$level_course = “Beginning”;

The dollar sign and variable name comes first, then an equals sign. After the equals sign, however, we have direct text – Beginning. But notice the double quotation marks around our text. If you don’t surround your direct text with quotation marks, then you’ll get errors. You can, however, use single quotes instead of double quotes. So you can do this:

$level_course = ‘Beginning’;

The equals sign is not really an equals sign. It’s called an assignment operator.

Note :

1. The equals sign is not really an equals sign. It’s called an assignment operator.
2. PHP does not require variables to be declared before being initialized.
3. Remember surround any direct text with quotation marks.

For example, we want to know how many sections we have discussed. If we have twenty sections, then we do the “telling” like this:

$number_sections = 20;

The dollar sign and variable name comes first, then an equals sign. After the equals sign, you tell your variable what it will be doing. Holding the number 20, in our case.

The equals sign is not really an equals sign. It’s called an assignment operator.

Note :

1. The equals sign is not really an equals sign. It’s called an assignment operator.
2. PHP does not require variables to be declared before being initialized.