processing arrays

Arrays, and looping over them:

         $frontRow = array( "Aaron", "Alvin", "Isaac" );
         echo $frontRow[1];

To loop over an array, use foreach:

         $countA = 0;
         foreach ($frontRow as $student) {
           if ($substr($student,0,1)==="A") {
             $countA = $countA + 1;
             }
           }
         echo $countA . " names start with 'A'.";

Don't loop over an array using numeric indices in php: Many times arrays have non-numeric indices ¹.

Example array-usage (including using strings-as-indices): php-ch02-simple.php.

An example function

video: arrays in php example: ol (24m45s)

Suppose we want to write a function that takes an array of strings, and returns a string: the HTML for an ordered list.

What is a good name for this function?
What test cases do we consider?

Note that part of your test case is deciding what is the desired amount of whitespace to be included in the answer.

echo "Actual:  ", ol( array() ), "\n";
echo "Desired: ",
"<ol type='1'>
</ol>", "\n";

echo "Actual:  ", ol( array( "Milk" ) ), "\n";
echo "Desired: ",
"<ol type='1'>
  <li>
    Milk
  </li>
</ol>", "\n";

echo "Actual:  ", ol( array( "Milk", "Eggs", "Ice Cream!" ) ), "\n";
echo "Desired: ",
"<ol type='1'>
  <li>
    Milk
  </li>
  <li>
    Eggs
  </li>
  <li>
    Eggs
  </li>
</ol>", "\n";

Once we have this, the code is straightforward:

/* ol: string[] → string
 * Return the html for an ordered list whose items are `$lis`.
 */
function ol( $lis ) {
    $lisSoFar = "";
    foreach( $lis AS $li ) {
        $lisSoFar .= "  <li>\n    $li\n  </li>\n";
        }
    return "<ol type='1'>\n$lisSoFar</ol>";
    }

Some thoughts about names:

The name ol is fine, but on the edge. toOL or itemsToOL would also be fine.
The parameter name lis is fine, but some might prefer items or listItems, which is also fine.

¹ Or, numeric indices that aren't contiguous. ↩

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