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PHP with MySQL Essential Training
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Understanding array pointers


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PHP with MySQL Essential Training

with Kevin Skoglund

Video: Understanding array pointers

Before we leave the topic of loops behind, I want to talk about array pointers and show you how they work. It may seem like a technical detail, but it will become important later when we start working with databases. PHP maintains a pointer that points to one of the items in an array. That item is referred to as the current item. By default, that's always the first item in the array. When we start looping through arrays using something like four each, PHP moves the pointer down the array as it assigns each value to the loop's variable. Moving the pointer to the next value is how PHP keeps track of which item you're working with now and what the next item is that it should give you after that.
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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

Understanding array pointers

Before we leave the topic of loops behind, I want to talk about array pointers and show you how they work. It may seem like a technical detail, but it will become important later when we start working with databases. PHP maintains a pointer that points to one of the items in an array. That item is referred to as the current item. By default, that's always the first item in the array. When we start looping through arrays using something like four each, PHP moves the pointer down the array as it assigns each value to the loop's variable. Moving the pointer to the next value is how PHP keeps track of which item you're working with now and what the next item is that it should give you after that.

But loops are not the only way to move pointers around. Let's take a look. Let's create ourselves a little workspace by using basic dot html. And we'll use Save As, and then we're going to create pointers.php. To begin with, let's just give ourselves a little area here, php, and we'll put in array of ages. I'll also change the title to be pointers. Alright. So this is the array that we were working with before. So the pointer, by default. The current item that's being pointed at in this array is the first item, four.

As we do a loop through there, the pointer moves. So, the first time, it's pointing at four. The second time through the loop, it's now pointing at eight. And then it's pointing at 15, and so on. It moves all the way down, and when it gets to the last one. Then it moves one more and says, oops, there's no more items, I must be done. And so the loop ends. We can take a look at this current pointer value by using the current function. So here it is, just current, and then we pass in the array. That'll tell us what the current value that it's pointing to is. Let's try that. Let's save it.

Let's go back to Firefox. And instead of break, let's open up pointers.php. So there it is, it is pointing at the item four, I've got the one if front of it just so we can tell between each of these tests that we run. So here's four, now we can tell the pointer to move to the next item manualy by using the next function. So here's, this is just simply next ages. We're just saying hey, advance the pointer for ages to point to the next item. And then will once again echo back what the current item it's pointing to is.

This time, I've got a 2 in front of it so we can tell the difference. I'll save that. Let's go here. And there it is. It's pointing at eight. See how that works? Let's go back and let's just do a couple more here. Let's tell it to go two more times and then we'll do a third one and we'll ask it what it is for the third time. All right. It went 2 this time, so we're at 16, so you've skipped over the 15, and now we're pointing at 16. We can also have it go backwards by using Prev, short for "previous," p-r-e-v, and that's going to move it backwards. So tell ages to go backwards one, and then we'll use number 4 to see what the value's at now.

And there it is, it's at 15, and my backwards one. We also have two more that we'll look at together, which are reset, so reset will move the pointer back to the first element, and end will tell it to shoot all the way to the end, the last element. I've numbered those 5 and 6, let's take a look at that real quick. There we are. The first element and the last element. And now, just so that we can see what happens when we're at the end, let's go ahead and do next one more time. So, here it is, it's at the end, we're going to call next after the last element,and that's going to be 7. Let's see what that gives us back.

Go to return. We get back nothing, right? So that's how it knows that it's done. When it retrieves the last item, the last item is null then it knows that it's done. Okay, so how is this useful? Let's take a look at a wild loop example that will illustrate how it works in practice and which is going to set the stage for working with database records. Switch back over here, and let's just put a br tag, and then we'll put in my while example. So, it's a while loop that moves the array pointer. This is very similar to what foreach does.

Notice that in the condition of our while loop, right here, this expression, that we're doing an assignment, not a comparison. That is a single equal sign, not a double equals. What we're doing, is we're. Assigning a value from current to age. And we're also testing then to see if that assignment was successful. If it returned a value, then the expression is going to evaluate to true. But if it returned null, in other words we got to the end of it, then this expression will evaluate to a Boolean false.

Null will be considered false. And so at that point it will exit. So what we're essentially saying is, get the item that the array pointer points to. Assign it to age. And if that is an item. If you successfully got one, then execute the loop. If you did not successfully get an item, well then exit the loop. We're all done. And then of course, we do have to increment inside the array using next. That'll move the pointer to the next item. So that now, current will fetch something different the next time through the loop. So as I said, this is how foreach works. So why not just use for each step? Well, I want you to see this technique because when we start working with databases, we are going to use something very similar.

We'll retrieve many rows of data from a database table as an array and then move through each row, advancing the pointer as we go. But we can't use foreach for this, because the database pointers are not exactly the same as the array pointers. They're similar, but not the same. And the database pointers are going to be moved by the database driver. Each time that we request a row. Each time that we do this assignment here. It's going to increment the pointer as soon as it finishes making that assignment. Foreach and next won't be able to move those database pointers.

They're going to work only on PHP arrays. Not on these database arrays that we'll be working with later. So let's just try out this code real quick. Let's save it. We'll go back to. Firefox, let's try and reload the page. Notice that nothing happened. Well why is that? Well, it because current is still pointing at null, remember? Current here was null, so what is it here? It's still null, nothing has changed. We need to reset the pointer back to the beginning for ages. And now. We come back here. You'll see that it zips back to the beginning, and it starts going through with each one for all the way through 'til it gets to 42, and then the last one is null so the loop ends.

So I hope you understand how pointers work, and this gives you some insight into how foreach works and also how you can manipulate those pointers yourself. But more importantly I want to make sure that you're familiar with this syntax using the wild loop, because that's what we're going to be using when we start working with databases.

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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