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PHP with MySQL Essential Training
Illustration by Don Barnett

Continue


From:

PHP with MySQL Essential Training

with Kevin Skoglund

Video: Continue

We've now taken a look at three types of loops. While loops, for loops, and foreach loops. In the next two movies, we're going to learn how to use the functions Continue and Break to get more utility and flexibility from these loops. We'll start with Continue. Continue is used inside a loop to skip the rest of the current iteration and to go immediately to the conditional valuation that starts the next iteration. It may sound silly, but for me, continue evokes the image of a Hollywood casting director shouting next in the middle of an audition. It's like saying, we've seen enough, thanks, let's skip ahead to the next one. To give you an example, let's imagine that we have a database of college students and our code is going to loop through them and send them all in email. But, if a student is already signed up for a biology course this semester. Then we aren't going to send them the email.
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  1. 4m 8s
    1. Welcome
      1m 0s
    2. Using the exercise files
      3m 8s
  2. 15m 6s
    1. What is PHP?
      3m 52s
    2. The history of PHP
      2m 51s
    3. Why choose PHP?
      4m 10s
    4. Installation overview
      4m 13s
  3. 54m 53s
    1. Overview
      2m 33s
    2. Working with Apache Web Server
      6m 56s
    3. Changing the document root
      7m 24s
    4. Enabling PHP
      6m 16s
    5. Upgrading PHP
      3m 30s
    6. Configuring PHP
      10m 3s
    7. Installing MySQL
      5m 46s
    8. Configuring MySQL
      7m 24s
    9. Text editor
      5m 1s
  4. 31m 25s
    1. Overview
      3m 27s
    2. Installing WampServer
      5m 46s
    3. Finding the document root
      2m 24s
    4. Configuring PHP
      8m 12s
    5. Configuring MySQL
      5m 45s
    6. Text editor
      5m 51s
  5. 19m 12s
    1. Embedding PHP code on a page
      6m 43s
    2. Outputting dynamic text
      5m 55s
    3. The operational trail
      2m 27s
    4. Inserting code comments
      4m 7s
  6. 1h 18m
    1. Variables
      7m 50s
    2. Strings
      4m 38s
    3. String functions
      8m 54s
    4. Numbers part one: Integers
      6m 27s
    5. Numbers part two: Floating points
      5m 25s
    6. Arrays
      10m 0s
    7. Associative arrays
      6m 37s
    8. Array functions
      6m 33s
    9. Booleans
      3m 50s
    10. NULL and empty
      5m 15s
    11. Type juggling and casting
      8m 27s
    12. Constants
      4m 43s
  7. 27m 37s
    1. If statements
      6m 0s
    2. Else and elseif statements
      4m 16s
    3. Logical operators
      7m 30s
    4. Switch statements
      9m 51s
  8. 42m 15s
    1. While loops
      8m 41s
    2. For loops
      5m 59s
    3. Foreach loops
      8m 16s
    4. Continue
      8m 28s
    5. Break
      4m 8s
    6. Understanding array pointers
      6m 43s
  9. 37m 25s
    1. Defining functions
      8m 25s
    2. Function arguments
      5m 32s
    3. Returning values from a function
      7m 33s
    4. Multiple return values
      4m 53s
    5. Scope and global variables
      6m 2s
    6. Setting default argument values
      5m 0s
  10. 20m 18s
    1. Common problems
      3m 47s
    2. Warnings and errors
      8m 36s
    3. Debugging and troubleshooting
      7m 55s
  11. 57m 57s
    1. Links and URLs
      5m 33s
    2. Using GET values
      5m 35s
    3. Encoding GET values
      8m 41s
    4. Encoding for HTML
      9m 26s
    5. Including and requiring files
      7m 40s
    6. Modifying headers
      6m 45s
    7. Page redirection
      6m 43s
    8. Output buffering
      7m 34s
  12. 1h 3m
    1. Building forms
      7m 28s
    2. Detecting form submissions
      5m 59s
    3. Single-page form processing
      7m 57s
    4. Validating form values
      10m 40s
    5. Problems with validation logic
      9m 54s
    6. Displaying validation errors
      7m 23s
    7. Custom validation functions
      6m 28s
    8. Single-page form with validations
      7m 25s
  13. 28m 5s
    1. Working with cookies
      2m 49s
    2. Setting cookie values
      5m 55s
    3. Reading cookie values
      6m 1s
    4. Unsetting cookie values
      4m 51s
    5. Working with sessions
      8m 29s
  14. 48m 39s
    1. MySQL introduction
      6m 43s
    2. Creating a database
      7m 41s
    3. Creating a database table
      7m 42s
    4. CRUD in MySQL
      5m 48s
    5. Populating a MySQL database
      7m 32s
    6. Relational database tables
      6m 40s
    7. Populating the relational table
      6m 33s
  15. 56m 4s
    1. Database APIs in PHP
      4m 51s
    2. Connecting to MySQL with PHP
      7m 45s
    3. Retrieving data from MySQL
      8m 47s
    4. Working with retrieved data
      6m 12s
    5. Creating records with PHP
      6m 58s
    6. Updating and deleting records with PHP
      9m 6s
    7. SQL injection
      3m 5s
    8. Escaping strings for MySQL
      6m 45s
    9. Introducing prepared statements
      2m 35s
  16. 35m 58s
    1. Blueprinting the application
      7m 19s
    2. Building the CMS database
      5m 14s
    3. Establishing your work area
      4m 38s
    4. Creating and styling the first page
      4m 22s
    5. Making page assets reusable
      6m 36s
    6. Connecting the application to the database
      7m 49s
  17. 32m 49s
    1. Adding pages to the navigation subjects
      5m 58s
    2. Refactoring the navigation
      6m 7s
    3. Selecting pages from the navigation
      6m 2s
    4. Highlighting the current page
      5m 26s
    5. Moving the navigation to a function
      9m 16s
  18. 1h 45m
    1. Finding a subject in the database
      9m 48s
    2. Refactoring the page selection
      10m 52s
    3. Creating a new subject form
      6m 55s
    4. Processing form values and adding subjects
      11m 20s
    5. Passing data in the session
      9m 16s
    6. Validating form values
      9m 40s
    7. Creating an edit subject form
      8m 30s
    8. Using single-page submission
      7m 44s
    9. Deleting a subject
      9m 44s
    10. Cleaning up
      10m 37s
    11. Assignment: Pages CRUD
      4m 30s
    12. Assignment results: Pages CRUD
      6m 10s
  19. 39m 26s
    1. The public appearance
      8m 52s
    2. Using a context for conditional code
      11m 37s
    3. Adding a default subject behavior
      6m 9s
    4. The public content area
      5m 51s
    5. Protecting page visibility
      6m 57s
  20. 1h 3m
    1. User authentication overview
      4m 3s
    2. Admin CRUD
      8m 41s
    3. Encrypting passwords
      7m 26s
    4. Salting passwords
      5m 42s
    5. Adding password encryption to CMS
      11m 54s
    6. New PHP password functions
      3m 13s
    7. Creating a login system
      11m 28s
    8. Checking for authorization
      5m 48s
    9. Creating a logout page
      5m 40s
  21. 2m 4s
    1. Next steps
      2m 4s

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PHP with MySQL Essential Training
14h 24m Beginner Jun 04, 2013

Viewers: in countries Watching now:

PHP is a popular, reliable programming language at the foundation of many smart, data-driven websites. This comprehensive course from Kevin Skoglund helps developers learn the basics of PHP (including variables, logical expressions, loops, and functions), understand how to connect PHP to a MySQL database, and gain experience developing a complete web application with site navigation, form validation, and a password-protected admin area. Kevin also covers the basic CRUD routines for updating a database, debugging techniques, and usable user interfaces. Along the way, he provides practical advice, offers examples of best practices, and demonstrates refactoring techniques to improve existing code.

Topics include:
  • What is PHP?
  • Installing and configuring PHP and MySQL
  • Exploring data types
  • Controlling code with logical expressions and loops
  • Using PHP's built-in functions
  • Writing custom functions
  • Building dynamic webpages
  • Working with forms and form data
  • Using cookies and sessions to store data
  • Connecting to MySQL with PHP
  • Creating and editing database records
  • Building a content management system
  • Adding user authentication
Subjects:
Developer Servers Programming Languages Web Development
Software:
MySQL PHP
Author:
Kevin Skoglund

Continue

We've now taken a look at three types of loops. While loops, for loops, and foreach loops. In the next two movies, we're going to learn how to use the functions Continue and Break to get more utility and flexibility from these loops. We'll start with Continue. Continue is used inside a loop to skip the rest of the current iteration and to go immediately to the conditional valuation that starts the next iteration. It may sound silly, but for me, continue evokes the image of a Hollywood casting director shouting next in the middle of an audition. It's like saying, we've seen enough, thanks, let's skip ahead to the next one. To give you an example, let's imagine that we have a database of college students and our code is going to loop through them and send them all in email. But, if a student is already signed up for a biology course this semester. Then we aren't going to send them the email.

So we start the loop, we check to see if the student has signed up for Biology, and if so then we know that we don't need to do any further processing at all. We can just skip to the next student record. That's what continue allows us to do. And it makes our code more efficient. Let's see an example. So let's open up basic.html and let's do Save As, and we're going to call this continue.php. I'll change this to continue. I'm going to start with just a basic for loop. So here's the same for loops we were looking at before. Just counting the numbers zero to ten and echoing them out.

We saw an example earlier where we said if the count is equal to five then do some different behavior. Right, we outputted something different. Instead this time I'm going to have it just do continue, that's our continue function. So, continue with a semicolon after it is the only thing. Let's save it and let's bring it up in our browser and look at what it looks like. So here I am in Firefox, and instead of 4 H loops, let's go to continue. There it is, I think this makes it really clear what continue does. We get to the number 4, and there is no number 5, it picks up again with 6.

Let's go back and look at the code. When it's for, well it doesn't meet this condition here, the if statement, so it outputs for. Then for gets incremented to 5. The count is still less than or equal to 10. Now the count is equal to 5 so we continue tells it to immediately loop. That increments the counter to 6, it checks and sees that 6 is less than or equal to 10, this time it echoes the 6. One way that you can think about it is that there's an implicit continue at the end of every loop.

Now we don't need to actually write it out there because it's built into the looping structure. But what we're doing in this case is we're telling it to loop earlier. Instead of having to wait till we get to the continue that's at the end of the loop to tell it to loop again. We have this continue here telling it to do it when we want. Now if you're doing something so simple as this, I just want to remind you that white space doesn't matter. Something like this would do just as well. I'm going to change this to be our modulo operator with percent 2 equals to 0. Let's just bring that up and try it. And that basically says that, we're going to print out the odd numbers, right? Whatever the remainder of dividing count by 2, is equal to 0, then we're going to continue.

We're going to skip over it, and we don't do anything, we don't do any further processing, and it never gets to this echo statement. Now you may be tempted to think that we could use an if statement instead. That we could do something like this. If the remainder of dividing by 2 is not equal to 0, then echo it out, otherwise don't, right? But that kind of misses the whole point of why continue is useful. With a simple, one line statement like this, they are practically the same. But imagine if our if statement had 100 lines of code in it. Then if I'm reading the code, I would need to scroll down 100 lines to find the end of the if statement. And then check to see if there's any other code that would be executed before the loop finishes.

With continue, we don't have to do that, we know what happens. As soon as the code gets to continue, the loop starts over again. It's explicit and it's definitive. It says simply we're done and we're moving on. It make our code clearer. Both easier to read and easier to understand. Let's try another example using a while loop. So here I've got a, a simple while loop. You can see that it;s basically the same as I had with my for loop. I've got my account being initialized. Here's my condition. When count is equal to less than 10. And I'm incrementing here, count++. I'm echoing the count just like I was before.

And I've gone back to the other version. Where the count is equal to 5 continue. But there's a big difference between this one and the one before. And that's why I've put, what's wrong with this, up here. Because this has a problem. Do you see what it is? You may want to pause the movie, and take a second to look at it. And see if you can figure it out. Walk through the loops with me step by step. Let's image that count is equal to four. That's less than or equal to 10, it's not equal to 5, so we output 4. Then 4 gets incremented, it becomes 5. We got back to the top of the loop, 5 is less than or equal to 10.

Now, count is equal to 5, so we continue. That goes back to the top of the loop, and it evaluates count is less than or equal to 10. What is count now? It's 5 still. We didn't increment it. So it comes down here, count is equal to 5, we get a continue, we go back. We check the condition, and when stuck in an infinite loop, we never get to this increment that's down here. With for loops that doesn't happen, because this incrementation is built in to the loop. It always does this last step with foreach loops it also is in a problem, because those always move to the next element in the array. But with while loops, it's not necessarily true. This incrementation is optional, it's up to us to provide it. So, what we really need to do is fix it by making sure that we still increment before we continue.

So when count is equal to 5, make it 6 and then go to the next one. As an important tip when working with while loops and continues, it's a gotcha that can sneak up when you're not watching for it. Okay, let's make sure that we fix that. We're not going to bring it up in the browser right now, but I want to show you one last example. because there's one more thing you need to know about continue, and that is how to work with continue when you have a loop inside a loop. So here I have one loop, I've got for, and I'm using i for my counter now. By the way, that's very common when we have loops, it's just to use a simple single letter variable. So i is counting from 0 to 5, then I've got my modulo operator here. So when we get to an even number it's going to use continue, then I've got another loop, loop inside a loop.

This one is going to use k and k is going to count from 0 to 5 and it's going to just echo out i with a hyphen and then k and then a br tag. Let's take a look and just see what it looks like on its own before we try doing more. Let's come back over to the browser, let's reload. You do want to make sure that you fix this problem up here before we come back and try it, otherwise you'll have an infinite loop. So you can see that the results I got are 1-0, 1-1, 1-2, 1-3, 1-4, 1-5 and then it jumps to 3-0 and then eventually 5-0, okay? So there's my series that I've generated. Now what I want to do now is I want to add another line here, right before the echo, and I'm going to do another continue.

Let's say if, k, talking about k here, is equal to 3. Not the modulo, but k is actually equal to 3. Then, let's continue, okay. So let's take a look at what that does. Come back over and reload it, and notice that now 1-3 is missing, 3-3 is missing, and 5-3 is missing, that makes sense. That's what we would expect to happen. Continue, continues this loop. Comes back to the top of this loop, therefor just skipping 3 essentially each time on the second loop. But what if we wanted this continue not to apply to the inner most loop, but to the outermost loop. What if we were essentially saying, look, we've got a whole bunch of loops going and processes, we're looking for something.

And once we find it, w want to tell the parent that it should continue. We don't need to keep doing any more of the loops here as well. Well, the way that we do that is we can provide an argument to continue. Put parentheses and then an integer inside of it. By default, continue has an integer of one as an argument, but if we provide another number, like 2. Then that tells it that it should continue, not just one loop, but 2 loops back. So don't just look for 1, go all the way back to this looping structure and continue that one.

So this is different, this one is the same as that one. I'll leave it in there just so that you see the difference. And then 2 is telling it to skip that one. Let's Save it and go back and reload our page and see what happens now. Now when it gets to 1-3, it doesn't do 1-4 and 1-5, it goes ahead and jumps to the next one, to the next iteration using 3. Go back and forth between those two if you need a little more time to understand the difference. Now that we understand how continue works, in the next movie we're going to take a look at break.

Find answers to the most frequently asked questions about PHP with MySQL Essential Training.


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Q: This course was revised on 6/4/2013. What changed?
A: The old version of this course was 6 years old and it was time for a complete revision, using PHP 5.4. (The tutorials will work with any version of PHP and covers any differences you might encounter). The author has also added updated installation instructions for Mac OS X Mountain Lion and Windows 8. The topics and end project are the same, but the code is slightly different. It also addresses frequently asked questions from the previous version.
 
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