IS 118 Introduction to Development Tools

IS 118 Introduction to Development Tools Chapter 5 Reusing Code IS 118

Things to Cover • Why reuse code • require() • include() • Variations IS 118

Why Reuse Code? • Lower Cost • The cost of writing code is high • Time to write • Time to check and debug • Time to document and implement • Cost of buying existing code is cheaper than writing it • Reliability • Normally if code is already in use it works! • Consistency • Its already done with the look we want IS 118

require() • reusable.php • <?php • echo ‘Here is a simple php statement. ; • ?> • To use: code in main.php • <?php • echo 'This is the main file. '; • require( 'reusable.php' ); • echo 'The script will end now. '; • ?> IS 118

Require() - 2 • This is the same as writing: • <?php • echo 'This is the main file. '; • echo ‘Here is a simple php statement. ; • echo 'The script will end now. '; • ?> IS 118

Require() -3 • Warnings: • Require just sticks the code in, if it is php it will be executed! • Could idea not to use other extensions • But maybe .inc – to help identify it • Need to use php tags, i.e. • <?php … ?> IS 118

Why use • Website templates • See home.html and home.php on CD IS 118

Calling Functions • Functions are like reusable code • Have already been written • Been debugged and documented • They work • Simple way to call: • function_name() • phpinfo() – info on installed version IS 118

Calling Functions • Prototype: • A prototype is a model of how to use the function • Resource fopen( string filename, string mode [, bool use_include_path [, resource zcontext]]) • NOTE: function names are NOT case sensitive • Name must be unique • The prototype defines the parameters to be passed IS 118

Parameters • Resource fopen( string filename, string mode [, bool use_include_path [, resource zcontext]]) • The first two parms are required • The next two are optional • Optional values – some or all can be provided IS 118

Scope • The scope is where a variable is visible and usable • Declared inside a function – only within that function (local variable) • Declared outside a function – available everywhere EXCEPT the function (global variables) • Superglobal variables – available everywhere including functions (chapter 1) IS 118

Scope – 2 • Can use keyword global to make a variable within a function have global scope • Can delete a variable by using unset() • Unset ( $variable_name) • It is no longer available in any scope IS 118

Scope – 3 pg 149 • Scope causes problems within functions • Function increment( $value, $amount = 1) { $value = $value +$amount; } • Does not work because you can not change the value of $value – not in scope! • Have to pass $value by reference • function increment( &$value, $amount = 1) • This works IS 118

Returning values • With in a function can use a return statement to end execution of it • But it also can return a value • Pg 151 – return $x, return false • Use as such: • echo larger ($a, $b).’ ’; • The function returns the larger vale and it is printed IS 118

Recursion • Recursion is a function that calls itself • Not used often is web based application • Used instead of iteration IS 118

IS 118 Introduction to Development Tools