CSCI 116 Functions

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

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

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);

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);

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

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

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; }

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”);

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);

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);

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);

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

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

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

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

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; ?>

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); ?>

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