ITEC 325 2012fall ibarland

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lect01b
php intro
functions; running via web server

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"

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 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");
?>

// 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.
  You may have to create that directory if it doesn't already exist, using mkdir.
• Make sure the file is world-readable, but not group-writable: chmod g-w blend.php.
• Make sure all the folders enclosing your file are other-executable but not group-writable: chmod g-w . .., chmod o+x . ...
• 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 " "; 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/~itec325/Lectures/php/lect01b-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.
• Finally, we see that since there are so many output statements in a php program, php has an alternate shortuct for intermingling output-data with other php statements: https://php.radford.edu/~itec325/Lectures/php/lect01b-blend-mixed.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 doesn't render a line-break unless there is an explicit “<br />” tag.

• blend-v1: a first version
• blend-v2: better test reporting (??)
• blend-v3: Using ternary-conditional to remove duplicate code
• blend-v4: Good testing again: a function to remove duplicate code
• blend-v5: Printing out html.
• blend-v6: Intermingled code/html.

The final program, cleaned up:

 1  <html>
 2  <head>
 3    <title>Rawr</title>
 4  
 5  
 6  <?php
 7  
 8  // Turn this flag off, to suppress output for test cases that pass:
 9  $SHOW_PASSED_TESTS = true;
10  // (Note that we will always run the test cases,
11  // and we'll always print any failed tests.)
12  //
13  // Also, for future: consider using a php constant instead of a variable:  
14  //    define('SHOW_PASSED_TESTS',true);    
15  // and then later refer to SHOW_PASSED_TESTS (no preceding $)
16  
17  
18  
19  
20  
21  /** Return a blend of two words:
22   * @param $word1 The word to take the first half from.
23   * @param $word2 The word to take the second half from.
24   * @return the first half of $word1 concatenated to the second half of $word2.
25   *   (If a word is odd length, we round the halfway-point down.)
26   */
27  function blend( $word1, $word2 ) {
28    $fHalf = substr($word1, 0, strlen($word1)/2 );
29    $lHalf = substr( $word2, strlen($word2)/2 );
30    return $fHalf . $lHalf;
31  }
32  
33  
34  /** Check whether the actual and expected values are the same.
35   * If not, print an error message.
36   * @param $actual  The actual result of the function-call.
37   * @param $expected  The expected (desired) result of the function-call.
38   */
39  function test($actual,$expected) {
40    global $SHOW_PASSED_TESTS;
41    if ($actual !== $expected) {
42      echo "Test failed:\n";
43      echo "Expected \"", $expected, "\",\n";
44      echo "but got  \"", $actual,   "\".\n";
45    }
46    else {
47      if ($SHOW_PASSED_TESTS) { echo "."; }
48    }
49  }
50  
51  
52  test( blend("a", ""),          "" );
53  test( blend("", "a"),          "a" );
54  test( blend("", "abc"),        "bc" );
55  test( blend("abc", ""),        "a" );
56  test( blend("", ""),           "" );
57  test( blend("a", "1"),         "1" );
58  test( blend("ab", "12"),       "a2" );
59  test( blend("motor", "hotel"), "motel" );
60  test( blend("smoke", "fog"),   "smog" );
61  test( blend("Ian", "Barland"), "Iland" );
62  ?>
63  </head>
64  
65  
66    <body>
67      Hi Ian Barland -- I shall call you <?php echo blend("Ian","Barland") ?>.
68      (How do you like that?)
69    </body>
70  
71  </html>

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©2012, Ian Barland, Radford University Last modified 2012.Aug.31 (Fri)

Please mail any suggestions (incl. typos, broken links) to ibarlandradford.edu