PHP: Functions II

Derek Bridge

Department of Computer Science,
University College Cork

PHP: Functions II

Aims:

• to better appreciate the different kinds of programmer-defined functions we might use

Overview

• In this lecture, we'll define more functions
• Look for examples where there are zero parameters, one parameter, and more parameters
• Look for examples where
  • the body of the function contains echo statements, assignment statements, conditional statements, and sequences of statements, as well as return statements
  • there is no return statement, or several return statements, rather than just a single return statement
• Look for examples where
  • a value is returned
  • no value is returned (void)
  and see the different ways these functions are invoked

Class exercise

• The Japanese dice game of Chõ-Han Bakuchi is played with two standard dice. Players bet on whether the sum of the two dice will be Chõ (even) or Han (odd)
• Suppose bakuchi.html contains this form:

  <form action="bakuchi.php" method="get">
      <input type="radio" name="bet" value="even" />
      <input type="radio" name="bet" value="odd" />    
      <input type="submit" />
  </form>

• On the next slide is a version of bakuchi.php which doesn't use any programmer-defined functions
  1. Rewrite it to use programmer-defined functions
  2. Give the prototypes of any functions you define
  3. Compare the two versions of the program

Version 1 (no programmer-defined functions)

$bet = $_GET['bet'];

if ( ( $bet == 'even' && ( rand(1, 6) + rand(1, 6) ) % 2 == 0 ) || 
     ( $bet == 'odd'  && ( rand(1, 6) + rand(1, 6) ) % 2 != 0 ) )
{
    echo '<p>You win!</p>';
}
else
{
    echo '<p>You lose!</p>';
}

Class exercise

• Define a function called output_paragraph, which takes in a string of text and echoes it within an HTML paragraph element
• Give its prototype
• Rewrite bakuchi.php to use this function

Class exercise

• Modify your output_paragraph function: if the value passed to it is the empty string, then it shouldn't output anything

Class exercise

• Define a function called output_section, which echoes a section containing a heading and some content
• Your function should have the following prototype:

  void output_section( string $id, int $level, 
                       string $heading, string $content )

  where
  • $id is the value of the section's id attribute
  • $level is the heading level we want (1-6)
  • $heading is the content of the heading element
  • $content is the rest of the content of the section

Example of invoking output_section

• If you invoke it like this

  output_section('intro', 2, 'Introduction', 
      '<p>Happy talk, keep talking happy talk.</p>');

• This is what it will echo:

  <section id="intro">
      <h2>Introduction</h2>
      <p>Happy talk, keep talking happy talk.</p>
  </section>

• (But without the nice indentation!)

Class exercise

• Define a function called get_larger, which takes in two numbers and uses a two-armed conditional to return the larger of the two
• Define an alternative version that uses a one-armed conditional instead
• Define a third version that uses the ternary conditional operator instead of if
• In fact, there is a built-in function which does the same (and more!), so we didn't need to write our own PHP: max