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Switch statements

From: PHP with MySQL Essential Training

Video: Switch statements

In this movie, we're going to be looking at a different kind of logical expression called Switch Statements. Switch statements are similar to if statements. In that they control the flow through our application. But they're going to have a different syntax, some different rules to follow. And a couple of special gotchas that we want to make sure that we watch out for. First, let's look at the basic syntax. We're going to use the function name, switch, followed by an argument. And that argument's going to be a value. This is the value that we're going to be testing through each of a series of test cases. So then in our curly braces we're going to list off those test cases.

Switch statements

In this movie, we're going to be looking at a different kind of logical expression called Switch Statements. Switch statements are similar to if statements. In that they control the flow through our application. But they're going to have a different syntax, some different rules to follow. And a couple of special gotchas that we want to make sure that we watch out for. First, let's look at the basic syntax. We're going to use the function name, switch, followed by an argument. And that argument's going to be a value. This is the value that we're going to be testing through each of a series of test cases. So then in our curly braces we're going to list off those test cases.

And each one is going to start with case, and then a test value to that we're going to test against value to see if their equal. And then a colon, and then a statement or series of statements that we want to execute. Then following that will be the next case that we want to test. So we'll test whether the values equal to test value two and if it is then we'll execute those statements. And then finally we have the option to provide a default case. If it doesn't match any of the above cases we're going to execute the statements that are defined by default. So, notice that we're dropping down each one of those cases, doing a test on each line.

It's very similar if we've written if, else if, and else. The big difference here is that we're testing equality. We're testing to see, is the value equal to test value 1, no? Okay, move down to the next one. Is value equal to test value 2? That's a very simple comparison of equality. There's no greater than or less than or anything like that. And usually, we're not working with Booleans. Because a bullion is either true or false, so there's really not a lot of test cases. Where you would see it more is it you had something like a string that could be many different things.

For example let's say that our customers had told us that the way that they wanted to be contacted. And they might have said that they wanted to be contacted by email or by phone or by some other message. Text message, Skype, something else, so we could have a switch statement that then executed a set of statements. Based on the way that they told us they wanted us to contact them. Now I only provided two case statements here and a default, but you can have as many cases as you need. You could just keep adding different cases each time. Now most times you're probably going to want if else statements.

You are going to use those way more often than switch statements. The switch statements are going to be very useful when you do have this kind of compact logic. Where you really are just saying, all right I want to test a value and that value can be ten different things. So I'm going to list off the ten different things that could happen if that value is each of those ten cases. And I'm going to provide code for those. The parallel structure can be a little bit easier to read, and to work with. Okay, now that we know the syntax and the basic idea, let's try some out. I'm going to create a new page where we can work these, I'm going to open up basic.html and I'll do Save As. And I'm going to call this switch.php.

Change the title will also be switch, and let's give ourselves a php area. Alright, so to start with, let's just give ourselves a variable. We'll call it a, and we're going to make a equal to 3. And then, let's do a switch statement. Switch and then send the variable n as the argument to switch. So we're going to be testing variable a. And in the case where it is 0, then we're going to echo a equals 0, will be our tag at the end, and semicolon after that. Okay, now let's take that same thing, and I'm going to Paste it here. And let's make our next case, that it's one, alright? See what we're doing here, see the parallel structure? I'm actually going to Copy both of those now.

Save myself some typing, and we're going to make this one 2, and this one 3. I'll change it both here and in the text, so there we go. Now we have our cases. Now remember I could also have a default case, for now I'm not going to do the default case. Let's just do the simple one. We're going to test whether it's 0, 1, 2, or 3. If it's not that, if it's 4, 5 or 6, well, then none of these will execute. And we'll just move on right past this whole statement. So let's Save it and let's try it out. Let's go back to Firefox, and instead of logical, we're going to look for switched.php.

A equals 3, perfect. See how that worked? It skipped right past these cases, it tested them. Said nope, nope, nope, yes, this one matches. So then it executed the statement. All right let's just try moving a and making a equal to 0. Let's see what happens here, Save it. Let's go back to Firefox and let's reload the page. Whoa, wait a minute, a equals 0. Well that's correct. It did match that case. But look what happened after that. It also came back and told us that it was equal to 1, 2, and 3. Which it's obviously not. And if we put another value in here, like 2.

Go back and reload the page. You'll see that it comes back and it executes the first one and every case that comes after it. It's an important point about the way that switch statements work. They do the statement that matches. And then they continue to match every one that comes below it. Well that's probably not what we wanted. So if you don't want that behavior, then you've got to provide a break statement. So break, break and break, after each one. Now when we go back, let's make it equal to 0 again, Save it, go back to Firefox and there it is, a equals 0. That's the behavior that we would expect.

Because we told it, okay, you've done your statement now break out of the switch statement. And that will then drop down here to the curly brace and keep going from there. So this break is super, super important when you're working with switch statements. Drill it into your head and you'll save yourselves a lot of debugging time. Now as I said, we can have a default case here as well. Default and then echo and then a is not 0, 1, 2 or 3. And we don't have to have a break here, because it's the last one.

But I'm going to go ahead just to keep the parallel structure, and also to keep reminding myself that, that break is very important to have. So I'll put it in there, now lets just try a is equal to 9. Go back to Firefox, and there it is. It's not equal to zero, one, two, or three. So you can see how that works, right? Now I'm going to set that back to 2, and let's just drop down here. And I want to show you another example. This example is going to output the Chinese zodiac, the year that it is in the Chinese zodiac. So to do that, we're going to do a little bit of a calculation. We're going to take the year, we're going to use 2013, and I'm going to subtract four from it, and do the modulo of that, using 12. That means that I'm finding the remainder once we divide it by 12. So after we divide it by 12 evenly, how many are left over? So that end result is going to be a single value. So even though I've got a calculation in here, it's a single value that comes through in the end, and that's what I'm testing.

So whatever that value is, whatever that remainder is it will check. If it's 0, then we are in the first year of the 12 year cycle, so it is the Year of the Rat. If it's a one, well then we know we're in the next year and the year is the Ox and so on. What I want to show you here, though, is that white space doesn't matter. Do you see the difference here? Up here, we had each one of these on a seperate line. Case 1 echo break, case 2 and so on. Here I've got them all one after another, very compact, very easy to read.

I've even added in some extra spaces here in front of the numbers to keep it all lined up nice, tight, easy to read. I've still got my colon. I've still got my semicolons to separate the commands and I've still got break, but the white space doesn't matter. Alright just so we can see that let's go ahead and bring that up in a browser. I'll put a br tag here at the end. It pops up and it says 2013 is the year of the snake. Now there's one last example that I want to show you, I'm going to Paste in another example here. Imagine that we have a user type. Let's go ahead and set a user type so we don't get an error. User type, and the user type is going to be equal to customer.

Right it could be customer it could be student. It could be press it could be something else. Well if that user type is student then we're going to echo back welcome. If its press then we're going to say greetings and if its customer then we're going to say hello to them. What I want to show you is what if you had multiple cases that you wanted to match on something. What if you wanted to have press and customer respond to the same set of statements. I mean we could say Hello and just do it there but this is a simple example imagine if this was in fact twenty lines of code, right? So, there's twenty lines of code, am I going to really repeat that twenty lines of code again? No, I don't really want to do that.

Now, this is the thing I want to caution you about. You may be tempted to do something like this, and to say case press customer, with commas between them. That's how you do it in some other languages. It's not how you do it in PHP, though. In PHP, if you want them to have the same one, well, guess what. You just put them one after another. Because what happens when press matches. It executes the statements that are here and then all the statements that are below it until it gets to a break. So press customer is going to do the same set of statements because of the way the switch works. You can see now why the switch statement behaves the way it does and why it needs you to put in that break some of the times.

Because there are cases when you're not going to use the break when you have multiple values like this. So we could have press, we could have customer, we could have case, when it's admin, right? We can just add more cases. And each one of those is going to do this block that's below it. So, let's save it and let's just try it. Let's go down here, we reload the page and there it is. Hello is what we get back as the result. That is the statement that goes with the case for customer. So, as I said, you're going to use if statements a lot more than your going to use switch statements.

But if you look up here it's something like this, where you have the Chinese zodiac. This is the classic case where you're going to want to use a switch statement. Writing if else statements for all of this just doesn't give you the same legibility and ease of maintaining the code as a switch statement does.

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This video is part of

Image for PHP with MySQL Essential Training
PHP with MySQL Essential Training

131 video lessons · 34108 viewers

Kevin Skoglund
Author

 
Expand all | Collapse all
  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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