IS 118 Introduction to Development Tools

1
IS 118 Introduction to Development Tools

• Chapter 5
• Reusing Code

2
Things to Cover

• Why reuse code
• require()
• include()
• Variations

3
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

4
require()

• reusable.php
• lt?php
• echo Here is a simple php statement.ltbr /gt
• ?gt
• To use code in main.php
• lt?php
• echo 'This is the main file.ltbr /gt'
• require( 'reusable.php' )
• echo 'The script will end now.ltbr /gt'
• ?gt

5
Require() - 2

• This is the same as writing
• lt?php
• echo 'This is the main file.ltbr /gt'
• echo Here is a simple php statement.ltbr /gt
• echo 'The script will end now.ltbr /gt'
• ?gt

6
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.
• lt?php ?gt

7
Why use

• Website templates
• See home.html and home.php on CD

8
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

9
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

10
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

11
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)

12
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

13
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

14
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).ltbr /gt
• The function returns the larger vale and it is
  printed

15
Recursion

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