PHP with MySQL Essential Training
Illustration by Don Barnett

Type juggling and casting


PHP with MySQL Essential Training

with Kevin Skoglund

Video: Type juggling and casting

During the previous movie we've been looking at different types in PHPs. So strings integers floats those are called types. And we've seen a few times when PHP converted a value from one type to another type for us. For example we were able to add a string to an integer and we saw that PHP converted a Boolean true to be the string one when it was output to our webpage. This process is referred to as Type Juggling. When PHP does it on the fly for us. We can also explicitly set a type ourselves. For example, converting a string one into the integer one.
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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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Watch the Online Video Course 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
Kevin Skoglund

Type juggling and casting

During the previous movie we've been looking at different types in PHPs. So strings integers floats those are called types. And we've seen a few times when PHP converted a value from one type to another type for us. For example we were able to add a string to an integer and we saw that PHP converted a Boolean true to be the string one when it was output to our webpage. This process is referred to as Type Juggling. When PHP does it on the fly for us. We can also explicitly set a type ourselves. For example, converting a string one into the integer one.

And when we do it, it's called Type Casting. And we can do type casting in two ways. We can do it using a function, we have the settype function for that purpose. And it's just settype and then in parentheses, two arguments. The item that's being cast into another type, comma, and the second argument is the type that we want to set it to. So in this case, it's going to either convert var to be an integer or make sure that it already is an integer. Notice the integer is in quotes, it's a string we're passing in. The other way that we can set type is by simply writing the name of the desired type in parentheses before the item being cast.

So for example, parentheses, integer, closed parentheses, space, and then the item that we want to cast. Notice that there's not quotes around integer in this case. We're just putting integer right there between the parentheses. It's not a string, it is just an instruction to PHP. And this is the syntax of how it's done in the C programming language, that's where this comes from. The types that we can use, the values that we can provide for typecasting, are the different types that we've seen so far. You've got string, integer, or int for short, float, array, boolean, or bool, for short. Now, for some of these, it's going to be kind of obvious if we're converting an integer to a float or an integer to a string.

It's pretty obvious the kind of conversion that it's going to make. But it's probably less obvious to you if you're going to convert the number 42 into a boolean or convert an array to a string. What that kind of result is going to give you. You can try them in an experiment to see, so you can get a feel for what they do. Or the website actually has a list of the rules that explains how it converts from 1 type to the other. So you can look those up. Let's create a page where we can do some experiements and play with both type juggling and type casting. So let's start by opening up basic.html, and we'll do Save As. I'm going to call this page type_casting.php, even though it's technically going to be for both type juggling and type casting. Type casting is probably the more common term that people use to refer to it, mostly because that's the thing that we have control over. So let's start out by just putting type Juggling in the html here. And then, lets put a bit of php in, we'll define, count is going to be equal to a string that is 2.

Okay, so, it's equal to a string and we can find out what type it is. We can certainly use is string is int, those kinds of queries that we learned when we were learning those types. An even better way to do it is to put echo gettype. So we're going to just ask it to get back the type of count for us. I'll put a br tag at then end. So that's going to report back. Now, we know what the type of that is, its pretty obvious. The, the type is a string. Even though it's a number, it's going to be a string. So now, let's do a little bit of PHP. And let's add count plus equals 3.

We saw this before when we were looking at integers. So let's do a gettype again. And then, let's just bring up that page, so we can have a look. Here we are instead of null, I need type_casting.php. So Type Juggling starts out being a string. And then it converts it to an integer. So count, got converted when we added plus 3 to it, right? The type was converted. It knew, even though you started with a string, i if I'm going to add these two things together, I'm going to need to have integers. And so it does the conversion for you. That's type juggling, PHP tries to make it work out for you. And we saw that if we had 2 cats for example, did the same thing. Reload the page, it still works just fine.

It still goes ahead and adds them together. We can output the count and you would see that it was equal to 5. And I can also see type juggling going back the other way. Let's convert our integer back to a string by concatenating it with two other strings. Here I have cats equal to a string, followed by what is now an integer. Remember, we ended up with an integer here, and then another string. And when we get gettype on that, we'll see what that returns to us. Lets bring this up, reload the page, and it's back to being a string again. And that's because it said hey, I'm going to concatenate as string, an integer, and a string. Well, if I'm doing concatenation, I need to turn those all into a string. And so it juggles back.

To a string for us. Now I think that this second one, using an integer to a string is not such a bad thing to do. And I think you'll see that happen a lot in people's PHP code. Because the conversion from an integer to a string is super simple, right? And it's something that we're probably going to be doing a lot. However, I think in other cases, like here, when we're converting a string into an integer, or, especially if we are doing more complex conversions. Maybe you're trying to convert an array into an integer, right, that seems like a much more extreme example. It's sloppy programming to to rely on php to do the switching for you. It's much better for you to make the change yourself. So, I wouldn't say that you can never do type juggling. Because I think you'll find me doing this kind of thing in my code all the time. But you won't find me doing this kind of thing in my code. I think that's the kind of thing, in my mind, that would be considered sloppy programming.

So, how do we make the change ourselves? Let's give ourselves the br tag here and then, let's do type casting br. So we talked about the two ways that we can do type casting. One is to use a function so we have the set type function. We are going to go ahead and use that same variable count but this time it ended up a string here. Now we are going to change it back into an integer. So we can do gettype on that and see what that is. So let's just bring that up and try it real quick. There you go, cast it back to an integer. It was a string, here we changed it back to an integer, the other way that we can do it is by using that declaration in front of it, right, string in parentheses.

This is not a string itself, it's just the word string inside parentheses, right before count, and I'm setting count2 equal to that value. And then we can compare. We can see what count equals, and what count2 equals. So let's bring this up and let's try it. There we go, now notice count one is still an integer. Count 2 is a string. And this is an important point about the difference between doing it these two different ways. Settype changes it in place. It actually just effects the variable right where it is, and changes its type. It recasts it in place.

This one does not do that and we can if we take this away, you would see the difference and you would see it doesn't recast it. Let's make that point a little more explicit. Let's just make a br tag here and I'll do php, dollar sign test1 is equal to the number 3. And then we'll do that same thing, but we'll make test2, so that we'll have two of them that are absolutely identical. And then, let's set the type both ways. So let's try the first one, we're going to use settype and we'll do it to test1.

And its type is going to be string, going to explicitly convert it. Then in the next one, let's just do it by putting string and then test2, kay? See what I'm doing? I'm setting the type both ways here. Now let's test the type for both of them. I'll just grab one of these lines up here, use that as a starting point. But we're going to call it test1, and test1 will echo back that value, and then do the same thing for test2.

Okay, so let's bring that up and let's take a look. Reload the page, and you see the first one was changed to a string. The second one was not changed. It's still is an integer. This change did not last. It only takes place as it's being used, in this case up here, as it's being assigned. The conversion is happening during assignment, it's not making a permanent change to the item itself. So, so it's important for us, while we're programming to be aware of what type something has, is it an integer, or is it a string? And then, to use type casting when we need to convert it to something else.

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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