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Logical operators

From: PHP with MySQL Essential Training

Video: Logical operators

In the last movie, we learned about basic logical expressions using if else and else if. Now, I want us to talk about the expression part of that, the part that evaluates to true to false. And I want us to enhance our ability to work with that to generate some more complex expressions. And to do that, we're going to have to learn about comparison and logical operators. In the previous example, we said if A is greater than B, or if A is less than B. Less than and greater than are comparison operators. But there are a number of other ones that we can use as well. One of the most important ones, is equal. Are two things equal? Compare them. Is A equal to B? It's made up of two equal signs. When we're testing if something is equal, we use it by using two equal signs. So, when we have one equal sign, we're doing assignment. We're assigning a value to something.

Logical operators

In the last movie, we learned about basic logical expressions using if else and else if. Now, I want us to talk about the expression part of that, the part that evaluates to true to false. And I want us to enhance our ability to work with that to generate some more complex expressions. And to do that, we're going to have to learn about comparison and logical operators. In the previous example, we said if A is greater than B, or if A is less than B. Less than and greater than are comparison operators. But there are a number of other ones that we can use as well. One of the most important ones, is equal. Are two things equal? Compare them. Is A equal to B? It's made up of two equal signs. When we're testing if something is equal, we use it by using two equal signs. So, when we have one equal sign, we're doing assignment. We're assigning a value to something.

When we have two of them, we're comparing the two. It's important to keep the two straight. One is for assignment, two is for comparison. We also have another version, which is three. Together which if for identical. Now, what's the difference between equal and identical? Well, there are some things that are considered equal because they're roughly equal. For example, the number 1, 2, 3 is considered equal to the string. One, two, three. Because if we convert the types, then they are considered equal but they are not considered identical.

Identical, they have to be of the same type as well. So, it just goes a little bit further in the check to make sure that they are absolutely 100% the same. Most times, you're going to find yourself just using equal though, with two of them. There's also comparison, we saw the greater than, less than. There is a greater than or equal to, or less than or equal to. Or there's it either less than or greater than. And of course, if we're going to do not equal to, we can also just simply say not equal using exclamation point equal. That exclamation point is going to mean not in PHP. We're going to see that again later on.

And then, of course, we also have not identical, which would be not followed by two equals signs. Notice that in each case, for equal and identical, what we're doing is replacing the first equal sign with that exclamation point. Now, in addition to using these to construct a single expression. To say is this equal to that or is this greater than that or this not equal to that. We also can combine several of these together by using some logical operators. So, for example, for and we can use two ampersands together.

What we're saying here is if A is greater than B, and if C is greater than D. They're testing two different things and combining them with this &. Both parts of it have to be true. If this is true and this is true, then the whole expression evaluates to true. We also have or that's made of these two upright bars, often called Pipes. Take a second to figure out where that is on your keyboard. It's typically right above the Return key. And this would be a logical or. So, if a is greater than b, or if c is greater than d. And then, of course, as we talked about, there's not. So, something is just not true, we can negate the expression just by putting the exclamation point in front of it.

It's basically just flips it around to be the opposite. Let's try a few example. Let's start just by opening up basic.html, and we'll do a save as. I'm going to call this one operators.php. And it's going to contain both our comparison operators and also our logical operators. Let me just drop down here in the body and I'll give you the first example. You can pause them if you need to copy this down. I've got a is equal to 4, b is equal to 3.

c is equal to 1 and d is equal to 20. Notice that those are assignments, using the single equal sign. Then, I've got my expression here. If a is greater than b, notice that I'm using parentheses around it to group it together, and if c greater than d. So, if both of those conditions are met, this and this, then this entire expression will evaluate to true. Because both parts have been met. So, both trues together mean that the whole thing is true. If either one is false, well then it's not a true statement. It's not true that both a is greater than b and c is greater than d. So, it evaluates to false.

So, let's just try this out. Let's bring this up in our browser. And instead of logical, we're going to go to operators. And you'll see that nothing is output. The reason why, a is greater than b. But c is not greater than d. So, let's just swap those real quick. We'll go back and try it again. There it is, a is larger than b, and c is larger than d. So, we can do the same thing with logical or by just putting in, the or and I'll just change this as well. So, now either one is true. If a is greater than b or c is greater than d. If either one of those is true, then it will work. Let's just flip this back to what didn't work before, right? So now, one of them is true, a is greater than b. But c is not greater than d.

Let's go back and reload it. So a is larger than b, or c is larger than d. That's what it output for us. So, as I said, we can also use some different comparison operators. We can say that one thing is equal to something. Something is equal to that. We can feel free to play around with those, and try different values. And see what you're going to get back. Let's try a, a real world example. I'm going to do one here for if and I'm going to use the not, right? The exclamation point, that means not the case. If isset, and I'll make it e. If not isset, right? That's the opposite. If it's not set, then we are going to set e equal to 200, then let's just echo back the value of e.

I'll put a br tag here just so it separates it out, so let's try this. Let's see if it inputs something for e. Switch back 200. Now, let's experiment here. Let's set e up here as well. Let's set e here equal to 100, okay? Let's go back and try it again. Now it's equal to 100, because it got here and it said oh, it's already been set. So, I don't need to give it a default value. This is a good way to set default values. If something's not set, well then set it.

Let's do another good, real world example here. Let's do one with empty. We talked about empty, and I said you have to be really careful when you're using empty. Let's say that we have a form coming in, and we don't want to reject zero or 0.0 as being invalid values. Well, we can say if the quantity entered is empty and if it is not numeric, then we say, you must enter a quantity. But if they've given us empty but it is numeric, right? It fails this part of it, then it's probably a zero or 0.0, and we'll allow it through. Let's just try real quick, quantity, and let's just set that equal to zero. And we'll add another br tag here just to separate it out nicely. There it is.

It didn't respond to it, but if we said for example that it was a blank string. Now, we go back rewrote it since you must enter a quantity. There's also the powerful combinations that can be made here. You can nest different logs. You want to use parentheses to help you group those together so that you can keep them straight. So, while these comparison operators and logical operators are really simple in themselves, they combine to develop some really powerful expressions. We can keep stringing them together, we can nest them inside each other, so that if all sorts of conditions are met. If the final evaluation is either true or false, we'll decide whether or not we execute some code.

And that's going to be a powerful thing.

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This video is part of

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PHP with MySQL Essential Training

131 video lessons · 32828 viewers

Kevin Skoglund
Author

 
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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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