Rawr

Suppose we want to write php code that blends two words, concatenating the first half of the first word and the second half of the second word: ¹

blend("motor", "hotel")  "motel"
blend("smoke", "fog")     "smog"

blend("Ian","Barland")   "Iland";

In the case of odd-length words, we'll "round down" the midpoint (this is handy since its what quotient (integer-division) by 2 does).

The first step in writing any program, as always, is to come up with test cases, including degenerate inputs.
(Why do we bother with trivial/degenerate inputs? To make any debugging easy: If the program we're going to write goofs up on the empty string, that will be an easy case to track down and debug.)

blend("a","")            ""
blend("","a")            "a"
blend("","abc")          "bc"
blend("abc","")          "a"
blend("","")             ""
blend("a","1")           "1"
blend("ab","12")         "a2"
blend("motor","hotel")   "motel"
blend("smoke","fog")     "smog"
blend("Ian","Barland")   "Iland"

In php:

The program is bracketed by with the processing instruction “<?php” and “?>”.
all variable-names start with a dollar sign.
We can call functions as you'd expect.
For the name of specific php string-processing functions, … just google "php string processing": ref.strings.php

<?php
  $fname = "Ian";
  $lname = "Barland";

  $fHalf = substr($fname, 0, strlen($fname)/2 );
  $lHalf = substr( $lname, strlen($lname)/2 );
  $theBlend = $fHalf . $lHalf;

  echo "Hi ", $fname, " ", $lname, ".\n";
  echo "I shall call you ", $theBlend;
?>

We can test this by running php blend.php from the command line.

We can make functions with the keyword “function”, curly-brackets, and “return”:

<?php 
  function blend( $fname, $lname ) {
    $fHalf = substr($fname, 0, strlen($fname)/2 );
    $lHalf = substr( $lname, strlen($lname)/2 );
    $theBlend = $fHalf . $lHalf;
    return $theBlend;
    }


  echo "Hi Ian Barland.  "
  echo "I shall call you ", blend("Ian","Barland");
?>

While we're busy writing functions, we can make an easy little function to actually run those test cases we created earlier:

// Print an error message if the two arguments
// aren't the same.
//
function test($actual,$expected) {
  if ($actual === $expected) {
    echo ".";
  }
  else {
    echo "Expected \"", $expected, "\",\n";
    echo "but got  \"", $actual,   "\".\n";
  }
}



test( blend("a","")           , "" );
test( blend("","a")           , "a" );
test( blend("","abc")         , "bc" );
test( blend("abc","")         , "a" );
test( blend("","")            , "" );
test( blend("a","1")          , "1" );
test( blend("ab","12")        , "a2" );
test( blend("motor","hotel")  , "motel" );
test( blend("smoke","fog")    , "smog" );
test( blend("Ian","Barland")  , "Iland" );

Final step: Let's put this program on the web!

Place the file inside dynamic_php/ on your H: drive.
Make sure the file is world-readable, but not group-writable: chmod g-w blend.php.

Most important: Make sure the program returns html. Remember that the web server will run the php program, and will return whatever the program prints/outputs to the client web browser.

// ... definitions of `blend` as above...

echo "";
echo "  Rawr";
echo "  ";
echo "Hi Ian Barland -- I shall call you ", blend("Ian","Barland"), "\n";
echo "(How do you like that?)";
echo "  ";
echo "";

We can view the page by visiting https://php.radford.edu/~ibarland/blend.php. Use view-source, and you'll see exactly what the program printed.. Note how the newline really is present in view-source — it's just that the browser ignores newlines. To get a linebreak seen inside the browser, our php program would have to print <br /> rather than \n.

The total program, cleaned up:

<?php

// A flag to turn the test-cases on/off.
define('RUN_TESTS',false);


/** Return a blend of two words:
 * @param $word1 The word to take the first half from.
 * @param $word2The word to take the first half from.
 * @return the first half of $word1 concatenated to the second half of $word2.
 *   (If a word is odd length, we round the halfway-point down.)
 */
function blend( $word1, $word2 ) {
  $fHalf = substr($word1, 0, strlen($word1)/2 );
  $lHalf = substr( $word2, strlen($word2)/2 );
  return $fHalf . $lHalf;
}


/** Check whether the actual and expected values are the same.
 * If not, print an error message.
 * @param $actual  The actual result of the function-call.
 * @param $expected  The expected (desired) result of the function-call.
 */
function test($actual,$expected) {
  if ($actual === $expected) {
    echo ".";
  }
  else {
    echo "Expected \"", $expected, "\",\n";
    echo "but got  \"", $actual,   "\".\n";
  }
}





if (RUN_TESTS) {
  test( blend("a", ""),          "" );
  test( blend("", "a"),          "a" );
  test( blend("", "abc"),        "bc" );
  test( blend("abc", ""),        "a" );
  test( blend("", ""),           "" );
  test( blend("a", "1"),         "1" );
  test( blend("ab", "12"),       "a2" );
  test( blend("motor", "hotel"), "motel" );
  test( blend("smoke", "fog"),   "smog" );
  test( blend("Ian", "Barland"), "Iland" );
  }


// Produce a valid web page:

echo "<html>";
echo "  <head><title>Rawr</title></head>";
echo "  <body>";
echo "    Hi Ian Barland -- I shall call you ", blend("Ian","Barland"), "\n";
echo "    (How do you like that?)";
echo "  </body>";
echo "</html>";
?>