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Unit 7: Functions

Objectives Notes

After studying this unit, you will be able to:

• Discuss user defined functions.
• Explain function scope.
• Understand returning values by value.

• Declaring function parameters.
• Explain default parameters.
• Discuss static variables.

• Explain arrays.
• Discuss objects.

Introduction

A function in PHP can be built-in or user-defined; however, they are both called the same way.
The general form of a function call is func(arg1,arg2,…). The number of arguments varies from
one function to another. Each argument be any valid expression, include other function calls.

Here is a simple example of a predefined function:
Example: $length = strlen(“Peter”);

strlen is a standard PHP function that returns the length of a string. Therefore,
$length is assigned the length of the string “Peter”: four.

Here’s an example of a function call being used as a function argument:
Example: $length = strlen(strlen(“Peter”));
You probably already guessed the result of this example. First, the
innerstrlen(“Peter”) is executed, which results in the integer 4. So, the code
simpli-fies to
$length = strlen(4);
Strlen ( ) expects a string and, therefore, (due to PHP’s magical auto conversion between types)
converts the integer 4 to the string “4”, and thus, the resulting value of $length is 1, the length
of “4”.

7.1 User-Defined Functions

The general way of defining a function is

function function_name (arg1, arg2, arg3, …)

statement list
}

To return a value from a function, you need to make a call to return expr inside your function.
This stops execution of the function and returns expr as the function’s value.

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