Publishers of technology books, eBooks, and videos for creative people

Home > Articles

This chapter is from the book

Creating and Calling Your Own Functions

As you've already seen, PHP has a lot of built-in functions for almost every need. More importantly, though, it has the capability for you to define and use your own functions for whatever specific purpose. The syntax for making your own function is

function function_name () {
   // Function code.
}

The name of your function can be any combination of letters, numbers, and the underscore, but it must begin with either a letter or the underscore. In PHP, as I mentioned in the first chapter, function names are case-insensitive (unlike variable names) so you could call that function using function_name() or FUNCTION_NAME() or function_Name(), etc.

The code within the function can do nearly anything, from generating HTML to performing calculations. In this chapter, I'll demonstrate both.

To create your own function:

  1. Create a new PHP document in your text editor (Script 3.5).
    <?php # Script 3.5 - dateform.php
    $page_title = 'Calendar Form';
    include ('./header.inc');
    
    This page will use the same HTML template as the previous one (index.php; refer to Script 3.4).
  2. Begin defining a new function.
    function make_calendar_pulldown() {
    
    The function I'll write here will generate the form pull-down menus for months, days, and years as in calendar.php (refer to Script 2.14). The name I give the function clearly states its purpose.
  3. Generate the pull-down menus.
    $months = array (1 => 'January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December');
    echo '<select name="month">';
    foreach ($months as $key => $value) {
       echo "<option value=\"$key\">$value</option>\n";
    }
    echo '</select>
    <select name="day">';
    for ($day = 1; $day <= 31; $day++) {
       echo "<option value=\"$day\">$day</option>\n";
    }
    echo '</select>
    <select name="year">';
    $year = 2003;
    while ($year <= 2010) {
       echo "<option value=\"$year\">$year</option>\n";
       $year++;
    }
    echo '</select>';
    
    This code is exactly as it was in the original script only it's now stored within a function.
  4. Close the function definition.
    } // End of the make_calendar_pulldown() function.
    
    In complicated code, it's a useful tool to place a comment at the end of the function definition so you know where a definition begins and ends.
  5. Create the form and call the function.
    echo '<form action="dateform.php" method="post">';
    make_calendar_pulldown();
    echo '</form>';
    
    This code will create the tags for the form and then call the make_calendar_pulldown() function, which will have the end result of creating the code for the three pull-down menus.
  6. Complete the PHP script by including the HTML footer.
    include ('./footer.inc');
    ?>
    
  7. Save the file as dateform.php, upload to your Web server (in the same folder as header.inc, footer.inc, and index.php), and test in your Web browser ( Figure 3.6 ).
    03fig06.gif

    Figure 3.6 The pull-down menus are generated by a function within an HTML template.

Creating a function that takes arguments

Just like PHP's built-in functions, those you write can take arguments (also called parameters). For example, the print() function takes what you want sent to the browser as an argument and strlen() takes a string whose character length will be determined.

A function can take any number of arguments that you choose, but the order in which you put them is critical. For your arguments, use variable names:

function function_name ($arg1, $arg2) {
  // Function code.
}

To call the function, use

function_name ('value', 'more values');
function_name ('value', $var);

As with any function in PHP, failure to send the right number of arguments results in an error ( Figure 3.7 ). Also, the variable names you use for your arguments are irrelevant to the rest of the script (as you'll discover in the Variable Scope section of this chapter), so be certain to use valid, meaningful names.

03fig07.gif

Figure 3.7 Failure to send a function the proper number or type of arguments is a common error.

To demonstrate this, I'll rewrite the calculator example from Chapter 2, "Programming with PHP," as a function (refer to Scripts 2.6 and 2.8).

To write functions that take arguments:

  1. Create a new PHP document in your text editor (Script 3.6).
    <?php # Script 3.6 - calculator.php
    $page_title = 'Calculator';
    include ('./header.inc');
    
  2. Exit out of the PHP and create the HTML form.
    ?>
    <form action="handle_calculator.php" method="post">
    <select name="quantity">
       <option value="">Select a quantity:</option>
       <option value="2">2</option>
       <option value="3">3</option>
       <option value="4">4</option>
       <option value="5">5</option>
       <option value="6">6</option>
    </select>
    <div align="left"><input type="submit" name="submit" value="Total!" /></div>
    <input type="hidden" name="price" value="19.95" />
    <input type="hidden" name="taxrate" value=".05" />
    </form>
    
    This simple HTML form allows the user to select a quantity upon which the order total will be calculated.
  3. Complete the page using the HTML footer.
    <?php
    include ('./footer.inc');
    ?>
    
  4. Save the file as calculator.php.
  5. Create another new PHP script in your text editor (Script 3.7).
    <?php # Script 3.7 -
    handle_calculator.php
    $page_title = 'Calculator';
    include ('./header.inc');
    
  6. Define the calculate_total() function.
    function calculate_total ($quantity, $price, $taxrate) {
       $total = ($quantity * $price) * ($taxrate + 1);
       $total = number_format ($total, 2);
       echo "<p>You are purchasing <b>$quantity</b> widget(s) at a cost of <b>\$$price</b> each. With tax, the total comes to <b>\$$total</b>.</p>\n";
    }
    
    This function performs the same calculations as the example in Chapter 2 and prints out the result. It takes three arguments: the quantity being ordered, the price, and the tax rate.
  7. Create the page's main conditional.
    if (is_numeric($_POST['quantity'])) {
       calculate_total ($_POST['quantity'], $_POST['price'], $_POST['taxrate']);
    } else {
       echo '<p><b>Please enter a valid quantity to purchase!</b></p>';
    }
    
    This conditional verifies if it received a valid quantity. If so, the calculate_total() function is called, which will determine and print the total. If not, an error message is sent to the Web browser.
  8. Finish the PHP page.
    include ('./footer.inc');
    ?>
    
  9. Save the file as handle_calculator.php, upload to your Web server along with calculator.php (store them in the same directory as the other files from this chapter), and test in your Web browser ( Figures 3.8 , 3.9 , and 3.10 ).
    03fig08.gif

    Figure 3.8 The HTML form in the Web template.

    03fig09.gif

    Figure 3.9 Calculations are made by the function that prints the result.

    03fig10.gif

    Figure 3.10 If no valid quantity was selected, an error message is printed.

Example 3.6. The calculator page is an extension of the one developed in Chapter 2, "Programming with PHP."

1   <?php # Script 3.6 - calculator.php
2
3   // Set the page title and include the HTML header.
4   $page_title = 'Calculator';
5   include ('./header.inc');
6   ?>
7
8   <form action="handle_calculator.php" method="post">
9
10  <select name="quantity">
11      <option value="">Select a quantity:</option>
12      <option value="1">1</option>
13      <option value="2">2</option>
14      <option value="3">3</option>
15      <option value="4">4</option>
16      <option value="5">5</option>
17      <option value="6">6</option>
18  </select>
19
20  <div align="left"><input type="submit" name="submit" value="Total!" /></div>
21
22  <input type="hidden" name="price" value="19.95" />
23  <input type="hidden" name="taxrate" value=".05" />
24
25  </form><!-- End of Form -->
26
27  <?php
28  include ('./footer.inc'); // Include the HTML footer.
29  ?>

Example 3.7. The handle_calculator.php script uses a function to perform its calculations.

1   <?php # Script 3.7 - handle_calculator.php
2
3   // Set the page title and include the HTML header.
4   $page_title = 'Calculator';
5   include ('./header.inc');
6
7   # ----------------------
8   // This function calculates a total based upon quantity, price, and tax and then prints the results.
9   function calculate_total ($quantity, $price, $taxrate) {

   10

   11      $total = ($quantity * $price) * ($taxrate + 1);

   12      $total = number_format ($total, 2);

   13      echo "<p>You are purchasing <b>$quantity</b> widget(s) at a cost of <b>\$$price</b> each. With tax, the total comes to <b>\$$total</b>.</p>\n";

   14

   15  } // End of calculate_total() function.
16  # ----------------------
17
18  // Main conditional.
19  if (is_numeric($_POST['quantity'])) { // Is the quantity a number?
20
21      calculate_total ($_POST['quantity'], $_POST['price'], $_POST['taxrate']);
22
23  } else { // Quantity is not a number.
24      echo '<p><b>Please enter a valid quantity to purchase!</b></p>';
25  }
26
27  include ('./footer.inc'); // Include the HTML footer.
28  ?>

Setting default argument values

Another variant on defining your own functions is to preset an argument's value.

function function_name ($arg1, $arg2 = 'Bob') {
   // Function code.
}

The end result of setting a default argument value is that that particular argument becomes optional when calling the function. If a value is passed to it, the passed value is used; otherwise, the default value is used.

You can set default values for as many of the arguments as you want, as long as those arguments come last in the function definition. In other words, the required arguments should always be first.

With the example function defined above, any of these will work:

function_name ($var1, $var2);
function_name ('Roberts');
function_name ('Doe', 'John');

However, function_name() will not work, and there's no way to pass $arg2 a value without passing one to $arg1 as well.

To set default argument values:

  1. Open handle_calculator.php (refer to Script 3.7) in your text editor.
  2. Change the function definition line (line 9) so that only the quantity is a required argument (Script 3.8).
    function calculate_total ($quantity, $price = 19.95, $taxrate = .05) {
    
    The $price and $taxrate variables—which were being sent as hidden inputs in the form—are now hard-coded in the function.
  3. Change the initial call to calculate_total() so that only the quantity is set.
    calculate_total ($_POST['quantity']);
    
    Since the price and tax rate values coming from the form are the same as those set as the default in the function, there's no need to pass these values to the function.
  4. Call the function again, using a different price and tax rate.
    calculate_total ($_POST['quantity'], 29.99, .0875);
    
    Even though default values are set, sending new ones will override them (this line is for contrast).
  5. Save the file, upload to your server, and test in your Web browser ( Figure 3.11 ).
    03fig11.gif

    Figure 3.11 The calculate_total() function is called twice, using different parameters.

Example 3.8. The calculate_total() function now assumes a set price and tax rate unless one is specified when the function is called.

1   <?php # Script 3.8 - handle_calculator.php
2
3   // Set the page title and include the HTML header.
4   $page_title = 'Calculator';
5   include ('./header.inc');
6
7   # ----------------------
8   // This function calculates a total based upon quantity, price, and tax and then prints the results.
9   function calculate_total ($quantity, $price = 19.95, $taxrate = .05) {
10
11      $total = ($quantity * $price) * ($taxrate + 1);
12      $total = number_format ($total, 2);
13      echo "<p>You are purchasing <b>$quantity</b> widget(s) at a cost of <b>\$$price</b> each. With tax, the total comes to <b>\$$total</b>.</p>\n";
14
15  } // End of calculate_total() function.
16  # ----------------------
17
18  // Main conditional.
19  if (is_numeric($_POST['quantity'])) { // Is the quantity a number?
20
21      calculate_total ($_POST['quantity']);

   22      calculate_total ($_POST['quantity'], 29.99, .0875);
23
24  } else { // Quantity is not a number.
25      echo '<p><b>Please enter a valid quantity to purchase!</b></p>';
26  }
27
28  include ('./footer.inc'); // Include the HTML footer.
29  ?>

Returning values from a function

The final attribute of a usable function that I should mention is that of returning values. Some, but not all functions, do this. For example, print() will return either a 1 or a 0 indicating its success, whereas echo() will not. The strlen() function returns a number correlating to the number of characters in a string.

To have your function return a value, use the return statement.

function function_name ($arg1, $arg2 = 'Bob') {
   // Function code.
   return $somevalue;
}

The function can return a value (say a string or a number) or a variable whose value has been created by the function. When calling this function, you should assign the returned value to a variable:

$var = function_name();

To have a function return a value:

  1. Open handle_calculator.php (refer to Script 3.8) in your text editor.
  2. Change the function definition to (Script 3.9)
    function calculate_total ($quantity, $price = 19.95, $taxrate = .05) {
       $total = ($quantity * $price) * ($taxrate + 1);
       return number_format ($total, 2);
    }
    
    This version of the function will return just the calculated total without any HTML or sending anything to the Web browser.
  3. Change the function call lines to
    $total = calculate_total ($_POST['quantity']);
    echo "<p>You are purchasing <b>{$_POST['quantity']}</b> widget(s) at a cost of <b>\${$_POST['price']}</b> each. With tax, the total comes to <b>\$$total</b>.</p>\n";
    
    Now the $total variable is being returned by the calculate_total() function and therefore the echo() statement has been reverted to its earlier form (using the superglobals).
  4. Save the file, upload to your server, and test in your Web browser ( Figure 3.12 ).
    03fig12.gif

    Figure 3.12 The script's main purpose can be achieved many different ways without affecting the end result.

Example 3.9. The calculate_total() function now takes up to three arguments and returns the calculated result.

1   <?php # Script 3.9 - handle_calculator.php
2
3   // Set the page title and include the HTML header.
4   $page_title = 'Calculator';
5   include ('./header.inc');
6
7   # ----------------------
8   // This function calculates a total based upon quantity, price, and tax and then returns the results.
9   function calculate_total ($quantity, $price = 19.95, $taxrate = .05) {
10
11      $total = ($quantity * $price) * ($taxrate + 1);
12      return number_format ($total, 2);
13
14  } // End of calculate_total() function.
15  # ----------------------
16
17  // Main conditional.
18  if (is_numeric($_POST['quantity'])) { // Is the quantity a number?
19
20      $total = calculate_total ($_POST['quantity']);
21      echo "<p>You are purchasing <b>{$_POST['quantity']}</b> widget(s) at a cost of <b>\$$_POST['price']</b> each. With tax, the total comes to <b>\$$total</b>.</p>\n";
22
23  } else { // Quantity is not a number.
24      echo '<p><b>Please enter a valid quantity to purchase!</b></p>';
25  }
26
27  include ('./footer.inc'); // Include the HTML footer.
28  ?>

Peachpit Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from Peachpit and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about Peachpit products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites; develop new products and services; conduct educational research; and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email ask@peachpit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by Adobe Press. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.peachpit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020