You are previewing Learning PHP, MySQL, JavaScript, and CSS, 2nd Edition.

Learning PHP, MySQL, JavaScript, and CSS, 2nd Edition

Cover of Learning PHP, MySQL, JavaScript, and CSS, 2nd Edition by Robin Nixon Published by O'Reilly Media, Inc.
  1. Learning PHP, MySQL, JavaScript, and CSS
  2. Dedication
  3. Preface
    1. Audience
    2. Assumptions This Book Makes
    3. Organization of This Book
    4. Supporting Books
    5. Conventions Used in This Book
    6. Using Code Examples
    7. Safari® Books Online
    8. How to Contact Us
    9. Acknowledgments
  4. 1. Introduction to Dynamic Web Content
    1. HTTP and HTML: Berners-Lee’s Basics
      1. The Request/Response Procedure
    2. The Benefits of PHP, MySQL, JavaScript, and CSS
      1. Using PHP
      2. Using MySQL
      3. Using JavaScript
      4. Using CSS
    3. The Apache Web Server
    4. About Open Source
    5. Bringing It All Together
    6. Test Your Knowledge
  5. 2. Setting Up a Development Server
    1. What Is a WAMP, MAMP, or LAMP?
    2. Installing a WAMP on Windows
      1. Testing the Installation
      2. Alternative WAMPs
    3. Installing a MAMP on OS X
      1. Configuring MySQL
      2. Testing the Installation
    4. Installing a LAMP on Linux
    5. Working Remotely
      1. Logging In
      2. Using FTP
    6. Using a Program Editor
    7. Using an IDE
    8. Test Your Knowledge
  6. 3. Introduction to PHP
    1. Incorporating PHP Within HTML
      1. Calling the PHP Parser
    2. This Book’s Examples
    3. The Structure of PHP
      1. Using Comments
      2. Basic Syntax
      3. Understanding Variables
      4. Operators
      5. Variable Assignment
      6. Multiple-Line Commands
      7. Variable Typing
      8. Constants
      9. The Difference Between the echo and print Commands
      10. Functions
      11. Variable Scope
    4. Test Your Knowledge
  7. 4. Expressions and Control Flow in PHP
    1. Expressions
      1. Literals and Variables
    2. Operators
      1. Operator Precedence
      2. Associativity
      3. Relational Operators
    3. Conditionals
      1. The if Statement
      2. The else Statement
      3. The elseif Statement
      4. The switch Statement
      5. The ? Operator
    4. Looping
      1. while Loops
      2. do…while Loops
      3. for Loops
      4. Breaking Out of a Loop
      5. The continue Statement
    5. Implicit and Explicit Casting
    6. PHP Dynamic Linking
      1. Dynamic Linking in Action
    7. Test Your Knowledge
  8. 5. PHP Functions and Objects
    1. PHP Functions
      1. Defining a Function
      2. Returning a Value
      3. Returning an Array
      4. Passing by Reference
      5. Returning Global Variables
      6. Recap of Variable Scope
    2. Including and Requiring Files
      1. The include Statement
      2. Using include_once
      3. Using require and require_once
    3. PHP Version Compatibility
    4. PHP Objects
      1. Terminology
      2. Declaring a Class
      3. Creating an Object
      4. Accessing Objects
      5. Constructors
      6. Writing Methods
      7. Declaring Properties
      8. Declaring Constants
      9. Property and Method Scope in PHP 5
      10. Inheritance
    5. Test Your Knowledge
  9. 6. PHP Arrays
    1. Basic Access
      1. Numerically Indexed Arrays
      2. Associative Arrays
      3. Assignment Using the array Keyword
    2. The foreach...as Loop
    3. Multidimensional Arrays
    4. Using Array Functions
      1. is_array
      2. count
      3. sort
      4. shuffle
      5. explode
      6. extract
      7. compact
      8. reset
      9. end
    5. Test Your Knowledge
  10. 7. Practical PHP
    1. Using printf
      1. Precision Setting
      2. String Padding
      3. Using sprintf
    2. Date and Time Functions
      1. Date Constants
      2. Using checkdate
    3. File Handling
      1. Checking Whether a File Exists
      2. Creating a File
      3. Reading from Files
      4. Copying Files
      5. Moving a File
      6. Deleting a File
      7. Updating Files
      8. Locking Files for Multiple Accesses
      9. Reading an Entire File
      10. Uploading Files
    4. System Calls
    5. XHTML
      1. The Benefits of XHTML
      2. XHTML Versions
      3. What’s Different?
      4. HTML 4.01 Document Types
      5. The HTML5 Document Type
      6. XHTML 1.0 Document Types
      7. XHTML Validation
    6. Test Your Knowledge
  11. 8. Introduction to MySQL
    1. MySQL Basics
    2. Summary of Database Terms
    3. Accessing MySQL via the Command Line
      1. Starting the Command-Line Interface
      2. Using the Command-Line Interface
      3. MySQL Commands
      4. Data Types
    4. Indexes
      1. Creating an Index
      2. Querying a MySQL Database
      3. Joining Tables Together
      4. Using Logical Operators
    5. MySQL Functions
    6. Accessing MySQL via phpMyAdmin
      1. Windows Users
      2. OS X Users
      3. Linux Users
      4. Using phpMyAdmin
    7. Test Your Knowledge
  12. 9. Mastering MySQL
    1. Database Design
      1. Primary Keys: The Keys to Relational Databases
    2. Normalization
      1. First Normal Form
      2. Second Normal Form
      3. Third Normal Form
      4. When Not to Use Normalization
    3. Relationships
      1. One-to-One
      2. One-to-Many
      3. Many-to-Many
      4. Databases and Anonymity
    4. Transactions
      1. Transaction Storage Engines
      2. Using BEGIN
      3. Using COMMIT
      4. Using ROLLBACK
    5. Using EXPLAIN
    6. Backing Up and Restoring
      1. Using mysqldump
      2. Creating a Backup File
      3. Restoring from a Backup File
      4. Dumping Data in CSV Format
      5. Planning Your Backups
    7. Test Your Knowledge
  13. 10. Accessing MySQL Using PHP
    1. Querying a MySQL Database with PHP
      1. The Process
      2. Creating a Login File
      3. Connecting to MySQL
    2. A Practical Example
      1. The $_POST Array
      2. Deleting a Record
      3. Displaying the Form
      4. Querying the Database
      5. Running the Program
    3. Practical MySQL
      1. Creating a Table
      2. Describing a Table
      3. Dropping a Table
      4. Adding Data
      5. Retrieving Data
      6. Updating Data
      7. Deleting Data
      8. Using AUTO_INCREMENT
      9. Performing Additional Queries
      10. Preventing SQL Injection
      11. Preventing HTML Injection
    4. Test Your Knowledge
  14. 11. Form Handling
    1. Building Forms
    2. Retrieving Submitted Data
      1. register_globals: An Old Solution Hangs On
      2. Default Values
      3. Input Types
      4. Sanitizing Input
    3. An Example Program
    4. Test Your Knowledge
  15. 12. Cookies, Sessions, and Authentication
    1. Using Cookies in PHP
      1. Setting a Cookie
      2. Accessing a Cookie
      3. Destroying a Cookie
    2. HTTP Authentication
      1. Storing Usernames and Passwords
      2. Salting
    3. Using Sessions
      1. Starting a Session
      2. Ending a Session
      3. Session Security
    4. Test Your Knowledge
  16. 13. Exploring JavaScript
    1. JavaScript and HTML Text
      1. Using Scripts Within a Document Head
      2. Older and Nonstandard Browsers
      3. Including JavaScript Files
      4. Debugging JavaScript Errors
    2. Using Comments
    3. Semicolons
    4. Variables
      1. String Variables
      2. Numeric Variables
      3. Arrays
    5. Operators
      1. Arithmetic Operators
      2. Assignment Operators
      3. Comparison Operators
      4. Logical Operators
      5. Variable Incrementing and Decrementing
      6. String Concatenation
      7. Escaping Characters
    6. Variable Typing
    7. Functions
    8. Global Variables
      1. Local Variables
    9. The Document Object Model (DOM)
      1. But It’s Not That Simple
      2. Using the DOM
    10. Test Your Knowledge
  17. 14. Expressions and Control Flow in JavaScript
    1. Expressions
      1. Literals and Variables
    2. Operators
      1. Operator Precedence
      2. Associativity
      3. Relational Operators
    3. The with Statement
    4. Using onerror
    5. Using try...catch
    6. Conditionals
      1. The if Statement
      2. The switch statement
      3. The ? Operator
    7. Looping
      1. while Loops
      2. do…while Loops
      3. for Loops
      4. Breaking Out of a Loop
      5. The continue Statement
    8. Explicit Casting
    9. Test Your Knowledge
  18. 15. JavaScript Functions, Objects, and Arrays
    1. JavaScript Functions
      1. Defining a Function
      2. Returning a Value
      3. Returning an Array
    2. JavaScript Objects
      1. Declaring a Class
      2. Creating an Object
      3. Accessing Objects
      4. The prototype Keyword
    3. JavaScript Arrays
      1. Numeric Arrays
      2. Associative Arrays
      3. Multidimensional Arrays
      4. Using Array Methods
    4. Test Your Knowledge
  19. 16. JavaScript and PHP Validation and Error Handling
    1. Validating User Input with JavaScript
      1. The validate.html Document (Part One)
      2. The validate.html Document (Part Two)
    2. Regular Expressions
      1. Matching Through Metacharacters
      2. Fuzzy Character Matching
      3. Grouping Through Parentheses
      4. Character Classes
      5. Some More Complicated Examples
      6. Summary of Metacharacters
      7. General Modifiers
      8. Using Regular Expressions in JavaScript
      9. Using Regular Expressions in PHP
    3. Redisplaying a Form After PHP Validation
    4. Test Your Knowledge
  20. 17. Using Ajax
    1. What Is Ajax?
    2. Using XMLHttpRequest
    3. Implementing Ajax via POST Requests
      1. The readyState Property
      2. The Server Half of the Ajax Process
    4. Using GET Instead of POST
    5. Sending XML Requests
      1. About XML
      2. Why Use XML?
    6. Using Frameworks for Ajax
    7. Test Your Knowledge
  21. 18. Introduction to CSS
    1. Importing a Style Sheet
      1. Importing a Style Sheet from Within HTML
    2. Embedded Style Settings
      1. Using IDs
      2. Using Classes
    3. CSS Rules
      1. Using Semicolons
      2. Multiple Assignments
      3. Using Comments
    4. Style Types
      1. Default Styles
      2. User Styles
      3. External Style Sheets
      4. Internal Styles
      5. Inline Styles
    5. CSS Selectors
      1. The Type Selector
      2. The Descendant Selector
      3. The Child Selector
      4. The Adjacent Sibling Selector
      5. The ID Selector
      6. The Class Selector
      7. The Attribute Selector
      8. The Universal Selector
      9. Selecting by Group
    6. The CSS Cascade
      1. Style Sheet Creators
      2. Style Sheet Methods
      3. Style Sheet Selectors
    7. The Difference Between <div> and <span>
    8. Measurements
    9. Fonts and Typography
      1. font-family
      2. font-style
      3. font-size
      4. font-weight
    10. Managing Text Styles
      1. Decoration
      2. Spacing
      3. Alignment
      4. Transformation
      5. Indenting
    11. CSS Colors
      1. Short Color Strings
      2. Gradients
    12. Positioning Elements
      1. Absolute Positioning
      2. Relative Positioning
      3. Fixed Positioning
      4. Comparing Positioning Types
    13. Pseudoclasses
    14. Pseudoelements
    15. Shorthand Rules
    16. The Box Model and Layout
      1. Setting Margins
      2. Applying Borders
      3. Adjusting Padding
      4. Object Contents
    17. Test Your Knowledge
  22. 19. Advanced CSS with CSS3
    1. Attribute Selectors
      1. Matching Parts of Strings
    2. The box-sizing Property
    3. CSS3 Backgrounds
      1. The background-clip Property
      2. The background-origin Property
      3. The background-size Property
      4. Multiple Backgrounds
    4. CSS3 Borders
      1. The border-color Property
      2. The border-radius Property
    5. Box Shadows
    6. Element Overflow
    7. Multicolumn Layout
    8. Colors and Opacity
      1. HSL Colors
      2. HSLA Colors
      3. RGB Colors
      4. RGBA Colors
      5. The opacity Property
    9. Text Effects
      1. The text-shadow Property
      2. The text-overflow Property
      3. The word-wrap Property
    10. Web Fonts
      1. Google Web Fonts
    11. Transformations
    12. Transitions
      1. Properties to Transition
      2. Transition Duration
      3. Transition Delay
      4. Transition Timing
      5. Shorthand Syntax
    13. Test Your Knowledge
  23. 20. Accessing CSS from JavaScript
    1. Revisiting the getElementById Function
      1. The O Function
      2. The S Function
      3. The C Function
      4. Including the Functions
    2. Accessing CSS Properties from JavaScript
      1. Some Common Properties
      2. Other Properties
    3. Inline JavaScript
      1. The this Keyword
      2. Attaching Events to Objects in a Script
      3. Attaching to Other Events
    4. Adding New Elements
      1. Removing Elements
      2. Alternatives to Adding and Removing Elements
    5. Using Interrupts
      1. Using setTimeout
      2. Canceling a Timeout
      3. Using setInterval
      4. Using Interrupts for Animation
    6. Test Your Knowledge
  24. 21. Bringing It All Together
    1. Designing a Social Networking Site
    2. On the Website
    3. functions.php
      1. The Functions
    4. header.php
    5. setup.php
    6. index.php
    7. signup.php
      1. Checking for Username Availability
    8. checkuser.php
    9. login.php
    10. profile.php
      1. Adding the “About Me” Text
      2. Adding a Profile Image
      3. Processing the Image
      4. Displaying the Current Profile
    11. members.php
      1. Viewing a User’s Profile
      2. Adding and Dropping Friends
      3. Listing All Members
    12. friends.php
    13. messages.php
    14. logout.php
    15. styles.css
  25. A. Solutions to the Chapter Questions
    1. Chapter 1 Answers
    2. Chapter 2 Answers
    3. Chapter 3 Answers
    4. Chapter 4 Answers
    5. Chapter 5 Answers
    6. Chapter 6 Answers
    7. Chapter 7 Answers
    8. Chapter 8 Answers
    9. Chapter 9 Answers
    10. Chapter 10 Answers
    11. Chapter 11 Answers
    12. Chapter 12 Answers
    13. Chapter 13 Answers
    14. Chapter 14 Answers
    15. Chapter 15 Answers
    16. Chapter 16 Answers
    17. Chapter 17 Answers
    18. Chapter 18 Answers
    19. Chapter 19 Answers
    20. Chapter 20 Answers
  26. B. Online Resources
    1. PHP Resource Sites
    2. MySQL Resource Sites
    3. JavaScript Resource Sites
    4. Ajax Resource Sites
    5. Miscellaneous Resource Sites
    6. O’Reilly Resource Sites
  27. C. MySQL’s FULLTEXT Stopwords
  28. D. MySQL Functions
    1. String Functions
      1. CONCAT()
      2. CONCAT_WS()
      3. LEFT()
      4. RIGHT()
      5. MID()
      6. LENGTH()
      7. LPAD()
      8. RPAD
      9. LOCATE()
      10. LOWER()
      11. UPPER()
      12. QUOTE()
      13. REPEAT()
      14. REPLACE()
      15. TRIM()
      16. LTRIM() and RTRIM()
    2. Date Functions
      1. CURDATE()
      2. DATE()
      3. DATE_ADD()
      4. DATE_FORMAT()
      5. DAY()
      6. DAYNAME()
      7. DAYOFWEEK()
      8. DAYOFYEAR()
      9. LAST_DAY()
      10. MAKEDATE()
      11. MONTH()
      12. MONTHNAME()
      13. SYSDATE()
      14. YEAR()
      15. WEEK()
      16. WEEKDAY()
    3. Time Functions
      1. CURTIME()
      2. HOUR()
      3. MINUTE()
      4. SECOND()
      5. MAKETIME()
      6. TIMEDIFF()
      7. UNIX_TIMESTAMP()
      8. FROM_UNIXTIME()
  29. Index
  30. About the Author
  31. Colophon
  32. Copyright
O'Reilly logo

Looping

One of the great things about computers is that they can repeat calculating tasks quickly and tirelessly. Often you may want a program to repeat the same sequence of code again and again until something happens, such as a user inputting a value or reaching a natural end. PHP’s various loop structures provide the perfect way to do this.

To picture how this works, take a look at Figure 4-4. It is much the same as the highway metaphor used to illustrate if statements, except that the detour also has a loop section that—once a vehicle has entered—can be exited only under the right program conditions.

Imagining a loop as part of a program highway layout

Figure 4-4. Imagining a loop as part of a program highway layout

while Loops

Let’s turn the digital car dashboard in Example 4-26 into a loop that continuously checks the fuel level as you drive using a while loop (Example 4-28).

Example 4-28. A while loop

<?php
$fuel = 10;

while ($fuel > 1)
{
    // Keep driving ...
    echo "There's enough fuel";
}
?>

Actually, you might prefer to keep a green light lit rather than output text, but the point is that whatever positive indication you wish to make about the level of fuel is placed inside the while loop. By the way, if you try this example for yourself, note that it will keep printing the string until you click the Stop button in your browser.

Note

As with if statements, you will notice that curly braces are required to hold the statements inside the while statements, unless there’s only one.

For another example of a while loop that displays the 12 times table, see Example 4-29.

Example 4-29. A while loop to print the 12 times table

<?php
$count = 1;

while ($count <= 12)
{
    echo "$count times 12 is " . $count * 12 . "<br />";
    ++$count;
}
?>

Here the variable $count is initialized to a value of 1, then a while loop is started with the comparative expression $count <= 12. This loop will continue executing until the variable is greater than 12. The output from this code is as follows:

1 times 12 is 12
2 times 12 is 24
3 times 12 is 36
...and so on...

Inside the loop, a string is printed along with the value of $count multiplied by 12. For neatness, this is also followed with a <br /> tag to force a new line. Then $count is incremented, ready for the final curly brace that tells PHP to return to the start of the loop.

At this point, $count is again tested to see whether it is greater than 12. It isn’t, but it now has the value 2, and after another 11 times around the loop it will have the value 13. When that happens, the code within the while loop will be skipped and execution will pass on to the code following the loop, which in this case is the end of the program.

If the ++$count statement (which could equally have been $count++) had not been there, this loop would have been like the first one in this section. It would never end, and only the result of 1 * 12 would be printed over and over.

There’s a much neater way that this loop can be written, though, which I think you will like. Take a look at Example 4-30.

Example 4-30. A shortened version of Example 4-29

<?php
$count = 0;
while (++$count <= 12)
    echo "$count times 12 is " . $count * 12 . "<br />";
?>

In this example, it was possible to remove the ++$count statement from inside the while loop and place it directly into the conditional expression of the loop. What now happens is that PHP encounters the variable $count at the start of each iteration of the loop and, noticing that it is prefaced with the increment operator, first increments the variable and only then compares it to the value 12. You can therefore see that $count now has to be initialized to 0, not 1, because it is incremented as soon as the loop is entered. If you keep the initialization at 1, only results between 2 and 12 will be output.

do…while Loops

A slight variation to the while loop is the do...while loop, used when you want a block of code to be executed at least once and made conditional only after that. Example 4-31 shows a modified version of our code for the 12 times table using such a loop.

Example 4-31. A do…while loop for printing the times table for 12

<?php
$count = 1;
do
    echo "$count times 12 is " . $count * 12 . "<br />";
while (++$count <= 12);
?>

Notice that we are back to initializing $count to 1 (rather than 0), because the code is being executed immediately, without an opportunity to increment the variable. Other than that, though, the code looks pretty similar to Example 4-29.

Of course, if you have more than a single statement inside a do...while loop, remember to use curly braces, as in Example 4-32.

Example 4-32. Expanding Example 4-31 to use curly braces

<?php
$count = 1;
do {
    echo "$count times 12 is " . $count * 12;
    echo "<br />";
} while (++$count <= 12);
?>

for Loops

The final kind of loop statement, the for loop, is also the most powerful, as it combines the abilities to set up variables as you enter the loop, test for conditions while iterating loops, and modify variables after each iteration.

Example 4-33 shows how you could write the multiplication table program with a for loop.

Example 4-33. Outputting the 12 times table from a for loop

<?php
for ($count = 1 ; $count <= 12 ; ++$count)
    echo "$count times 12 is " . $count * 12 . "<br />";
?>

See how the entire code has been reduced to a single for statement containing a single conditional statement? Here’s what is going on. Each for statement takes three parameters:

  • An initialization expression

  • A condition expression

  • A modification expression

These are separated by semicolons, like this: for (expr1 ; expr2 ; expr3). At the start of the first iteration of the loop, the initialization expression is executed. In the case of the times table code, $count is initialized to the value 1. Then, each time around the loop, the condition expression (in this case, $count <= 12) is tested, and the loop is entered only if the condition is TRUE. Finally, at the end of each iteration, the modification expression is executed. In the case of the times table code, the variable $count is incremented.

All this structure neatly removes any requirement to place the controls for a loop within its body, freeing it up just for the statements you want the loop to perform.

Remember to use curly braces with a for loop if it will contain more than one statement, as in Example 4-34.

Example 4-34. The for loop from Example 4-33 with added curly braces

<?php
for ($count = 1 ; $count <= 12 ; ++$count)
{
    echo "$count times 12 is " . $count * 12;
    echo "<br />";
}
?>

Let’s compare when to use for and while loops. The for loop is explicitly designed around a single value that changes on a regular basis. Usually you have a value that increments, as when you are passed a list of user choices and want to process each choice in turn. But you can transform the variable any way you like. A more complex form of the for statement even lets you perform multiple operations in each of the three parameters:

for ($i = 1, $j = 1 ; $i + $j < 10 ; $i++ , $j++)
{
    // ...
}

That’s complicated and not recommended for first-time users. The key is to distinguish commas from semicolons. The three parameters must be separated by semicolons. Within each parameter, multiple statements can be separated by commas. Thus, in the previous example, the first and third parameters each contain two statements:

$i = 1, $j = 1  // Initialize $i and $j
$i + $j < 10    // Terminating condition
$i++ , $j++     // Modify $i and $j at the end of each iteration

The main thing to take from this example is that you must separate the three parameter sections with semicolons, not commas (which should be used only to separate statements within a parameter section.)

So, when is a while statement more appropriate than a for statement? When your condition doesn’t depend on a simple, regular change to a variable. For instance, if you want to check for some special input or error and end the loop when it occurs, use a while statement.

Breaking Out of a Loop

You can break out from a for loop using the same break command you use to break out of a switch statement. This step can be necessary when, for example, one of your statements returns an error and the loop cannot continue executing safely.

One case in which this might occur is when writing a file returns an error, possibly because the disk is full (see Example 4-35).

Example 4-35. Writing a file using a for loop with error trapping

<?php
$fp = fopen("text.txt", 'wb');

for ($j = 0 ; $j < 100 ; ++$j)
{
    $written = fwrite($fp, "data");
    if ($written == FALSE) break;
}

fclose($fp);
?>

This is the most complicated piece of code that you have seen so far, but you’re ready for it. We’ll look into the file handling commands in a later chapter; for now all you need to know is that the first line opens the file text.txt for writing in binary mode and then returns a pointer to the file in the variable $fp, which is used later to refer to the open file.

The loop then iterates 100 times (from 0 to 99), writing the string data to the file. After each write, the variable $written is assigned a value by the fwrite function representing the number of characters correctly written. But if there is an error, the fwrite function assigns the value FALSE.

The behavior of fwrite makes it easy for the code to check the variable $written to see whether it is set to FALSE and, if so, to break out of the loop to the following statement closing the file.

If you are looking to improve the code, the line:

if ($written == FALSE) break;

can be simplified using the NOT operator, like this:

if (!$written) break;

In fact, the pair of inner loop statements can be shortened to the following single statement:

if (!fwrite($fp, "data")) break;

The break command is even more powerful than you might think. If you have code nested more than one layer deep that you need to break out of, you can follow the break command with a number to indicate how many levels to break out of, like this:

break 2;

The continue Statement

The continue statement is a little like a break statement, except that it instructs PHP to stop processing the current loop and to move right to its next iteration. So, instead of breaking out of the whole loop, only the current iteration is exited.

This approach can be useful in cases where you know there is no point continuing execution within the current loop and you want to save processor cycles, or prevent an error from occurring, by moving right along to the next iteration of the loop. In Example 4-36, a continue statement is used to prevent a division-by-zero error from being issued when the variable $j has a value of 0.

Example 4-36. Trapping division-by-zero errors using continue

<?php
$j = 10;

while ($j > −10)
{
$j--;
if ($j == 0) continue;
echo (10 / $j) . "<br />";
}
?>

For all values of $j between 10 and −10, with the exception of 0, the result of calculating 10 divided by $j is displayed. But for the particular case of $j being 0, the continue statement is issued and execution skips immediately to the next iteration of the loop.

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