1. CSCI 116
Functions

2. Functions A group of statements that you can execute as a single unit
May or may not accept parameters
An input to the function
Placed inside parentheses
May or may not return a value
An output of the function

3. Built-in Functions See http://php.net/manual
Type function name in Search box
parameters
array explode ( string $delimiter , string $string [, int $limit ] )
return
value
optional

4. Invoking a Function Pass an argument for each parameter
“Capture” a return value, if there is one
Assign to a variable
As an argument of another function
In a print or echo statement
In a decision
$str = “Tom^Dick^Harry”;
$arr = explode (“^”, $str);
print_r($arr);

5. Built-in Functions What are the parameters?
What are the return values?
How might you invoke the function?
addslashes
string addslashes ( string $str )
$newPhrase = addslashes($oldPhrase);
pow
number pow ( number  $base ,  number $exp )
if(pow(2, 3) > 5) …
str_repeat
string str_repeat ( string $input , int $multiplier )
print str_repeat(“Hello”, 5);
rand
int rand ( int $min , int $max )
$randomNumber = rand(1, 10);

6. A function may have zero or more parameters
Defining Functions
<?php function name_of_function(parameters) { statements; } ?>
A function may have zero or more parameters

7. Function Example function printPhrase($phrase) {
defining the function:
function printPhrase($phrase) {
echo “<p>$phrase</p>”; }
printPhrase(“Silly goose!”);
invoking the function:

8. Returning Values
A return statement returns a value to the statement that called (invoked) the function
A function does not have to return a value
function averageNumbers($a, $b, $c) {
$sumOfNumbers = $a + $b + $c;
$average = $sumOfNumbers / 3;
return $average; }

9. Function Practice
Define a function greeting that takes a name as a parameter and prints “Hello, name!”. (This function has no return value.) Invoke the function
function greeting($name) {
print “Hello, $name!”; }
greeting(“Sam”);

10. Function Practice
Write a function average that returns the average of two values. Invoke the function.
function average($num1, $num2) {
$avg = ($num1 + $num2)/2;
return $avg; }
$a = 5;
$b = 3;
print “The average of $a and $b is ” . average($a, $b);

11. Function Practice
Write a function largest that returns the maximum of two values. Invoke the function.
function largest($num1, $num2) {
if($num1 > $num2)
return $num1;
else
return $num2; }
$a = 5;
$b = 3;
print “The largest of $a and $b is ” . largest($a, $b);

12. Function Practice
Write a function circumference that takes a radius and returns the circumference of a circle (C=3.14*Diameter). Invoke the function.
function circumference($radius) {
$circ = 3.14 * 2 * $radius;
return $circ; }
$radius = 5;
print “The circumference is ” . circumference($radius);

13. Setting Default Parameter Values
defining the function:
function printPhrase($phrase = “Quack”) {
echo “<p>$phrase</p>”; }
printPhrase();
invoking the function:

14. Understanding Variable Scope
Where in your program a declared variable can be used
Can be either global or local
Global variable
Declared outside a function and available to all parts of your program
Local variable
Declared inside a function and only available within that function

15. Variable Scope <?php $globalVar = "Global"; function scopeExample(){
global $globalVar;
echo "<b>Inside function:</b><br />";
$localVar = "Local";
echo "$localVar<br />";
echo $globalVar.”<br /><br />"; }
scopeExample();
echo "<b>Outside function:</b><br />";
echo "$globalVar<br />";
?>
global keyword
used inside
function to
reference
global variable

16. Variable Scope <?php $globalVar = "Global"; function scopeExample(){
echo "<b>Inside function:</b><br />";
$localVar = "Local";
echo "$localVar<br />";
echo $GLOBALS[‘globalVar’].”<br /><br />"; }
scopeExample();
echo "<b>Outside function:</b><br />";
echo "$globalVar<br />";
?>
$GLOBALS array
used inside
function to
reference
global variable

17. Include Files <?php /* circumference takes a radius
functions.php
Include Files
<?php
/* circumference takes a radius
* and returns the circumference
* of a circle. */
function circumference($radius) {
$circ = 3.14 * 2 * $radius;
return $circ; }
/* area takes a radius and returns
* the area of a circle.
function area($radius)
$area = 3.14 * pow($radius, 2);
return $area;
?>

18. Include Files <?php include 'functions.php'; $radius = 5;
testScript.php
<?php
include 'functions.php';
$radius = 5;
print "The circumference is " .
circumference($radius);
print "The area is " . area($radius);
?>

19. Why use Functions? Reusability Functions make your code:
The same function can be used more than once
Within the same script
Across different scrips
Function libraries
Functions make your code:
Easier to read
Easier to modify
Easier to maintain