PHP 2: Variables

Variables in PHP begin with a $ symbol, for example:

• $myinteger
• $myfloat
• $mystring
• $myboolean

Variables are assigned values with the = operator, for example:

• $myinteger=6;
• $myfloat=3.14159;
• $mystring='I wandered lonely as a cloud';
• $myboolean=true;

Note that variable names in PHP are case-sensitive so $myboolean is distinct from $MyBoolean.

Like other scripting languages PHP is weakly typed, that is variables are assigned a type when they are initialised and can change types according to the value assigned. This cannot happened in strongly types languages such as Pascal, Java and C++ where variable types are declared in advance and cannot change.

Operators for numeric variables include:

• + and -
• * and /
• % (modulus)
• ++ and -- (increment & decrement)

There are many functions available for using with numbers, for example round() and number_format.

• $myfloat=3.14159
• $myfloat=round($myfloat)
• $myfloat=round($myfloat,2)

The number_format function inserts commas for thousands and also allows the number of decimal places to be specified:

• $myfloat=314159
• $myfloat=number_format($myfloat)
• $myfloat=round($myfloat,2)

Numeric variables can be used in calculations such as:

$total=$quantity * $price

Strings are assigned with = and can be output with echo, print and printf. They can be concatenated using the . operator (not + as in most other languages). For example:

• $firstname="Billy"
• $lastname="The Kid"
• $fullname=$firstname . $lastname
• $fullname=$lastname . ',' . $firstname

Here is some output of variables:

First Name: Billy
Last Name: The Kid
Full Name: BillyThe Kid

Here is the code:

Note the concatenation operator '.'

Some more variables on a new page:

Try it!

Constants are used to provide information that does not change in the course of a program (as distinct from a variable whose contents vary). Constants are defined with the define function, for example:

define ('MYNAME', 'Walter Smurfit');

Now 'MYNAME' can be used anywhere in the PHP code and will always contain 'Walter Smurfit'.