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If statements

From: PHP with MySQL Essential Training

Video: If statements

In this chapter, we're going to be looking at how we can start to control the flow of our code. To have our code make choices about what should happen based on certain conditions. And we're going to do that by using logical expressions. The most common of all types of logical expression, is the if statement,. This is the basic format of an if statement in PHP. We've got if followed by in parentheses an expression. And that expression is going to evaluate to either true or false. It's going to have a Boolean result. So if the expression is true, then the statement that follows it will be executed.

If statements

In this chapter, we're going to be looking at how we can start to control the flow of our code. To have our code make choices about what should happen based on certain conditions. And we're going to do that by using logical expressions. The most common of all types of logical expression, is the if statement,. This is the basic format of an if statement in PHP. We've got if followed by in parentheses an expression. And that expression is going to evaluate to either true or false. It's going to have a Boolean result. So if the expression is true, then the statement that follows it will be executed.

If it evaluates to false, then the statement will not be executed. And the code will skip past it and keep on evaluating down the rest of the PHP after it. So for example, if we have if a is greater than b, then echo back a is larger than b. So if the expression a is greater than b evaluates to true, then we'll get something echoed. If it's not true, then the echo line will never execute. PHP will just ignore it and move right on past it. Now, this format that I'm showing you here works if the statement portion that's going to be executed is just a single line. If you have more than one line of code that you want to execute for the statement portion, then you'll want to use curly braces around that statement. This makes it clear that everything inside the braces should be executed if the expression evaluates to true.

It's required for multi line statements but it's also considered a best practice to add them around single line statements too. It's clearer and I also think it's easier to develop using one style and just to stick with it. So always use curly braces. Notice also that I've indented the statement portion. PHP doesn't care about the indentation. Remember whitespace doesn't matter to PHP. But indentation is going to help us a lot because it's going to improve code readability. It's also going to help me to make sure that for every open and curly brace, that I have a matching closing curly brace. And we start nesting these inside of each other, it can sometimes to be hard to tell, and easy to lose track of them.

So let's start with those two good programming habits, always using curly braces, and always indenting our code. Let's try some if statement for ourselves. So here I am in my sandbox and I'm just going to open up basic.html. I'm going to choose Save As. Then I'm going to call this logical.php and save that in my sandbox. Logical. So let's just try the example that we just saw there. So we have php and in it, we're going to define a is equal to 4.

And let's have b and have that be equal to 3. And then we'll write our statement. If a is greater than b. Use my curly braces. Notice that it indented for me, TextMate does that helpfully. Echo a is larger than b. Okay so that's my statement. Let's go and try this out and see how it works. Switch back over to Firefox and I'm going to be going over to localhost/~kevinskoglund/sandbox/logical.php.

A is larger than b. Now you can play with those values, and we can say all right, let's set these in reverse. Let's go back, and let's reload the page, and notice that it doesn't output anything. It only evaluates what's inside the curly braces if this statement is true Alright, simple enough. Alright, lets try some some, some more maybe real world examples. Something a little less experimental. Lets say that we, have the website and we want to have a special welcome message, that displays only to new users of the website.

So we determine whether someone is a new user or not, in this case im going to say that it's true, If that is true, then we're going to display this welcome message to them. So we can experiment with that, you can try this from true to false and back again, but let's just go over here, try it out in our browser, and you'll see that we get our welcome message, because it was true. Another good example, you remember that we talked about that you can't divide by 0/ That gives you problems? Well, here's a way to check that. Our numerator that's 20, the denominator that's 4 If the denominator is greater than zero, than it's okay to proceed with the division. If it isn't greater than zero, then we may have a problem here, because this can't be zero.

Now I realize that this doesn't account for negative numbers, but you still get the point, you see what I'm saying, that it is not letting you divide by zero before it gives you the result. Let's just try that one out real quick. It says no problem, I can go ahead and I can do that division. Now, notice that the echo for result is occurring inside this if statement. I just want to move that out of there, so that you see what happens if I do this, alright. So it doesn't do the division, but it's going to echo, then, the result here. Let's go back and see what happens when we blow that up. It works just fine. But if I now make the denominator into zero, so that it would not execute this statement, right? Because now this fails, this is false. Let's come back over here, and let's reload the page. And you'll see, oops, undefined variable.

And the result, no result there. So notice that the result. Is being defined in the "if" statement. That's an important point. If we're defining variables in the "if" statement, then we need to make sure that we account for the possibility that result is not set, right? So we're going to start with a result of 0, and then, that way result will still have a value. Because this code. Does not execute at all if that statement is not true. So you'll want to watch for that. Think about the sort of path through your code. If the if statement doesn't execute, none of the variables and assignments that you make in there are going to be available to you.

Okay, let's go back up here to the top and you see that we've got this if a is greater than b. So if we wanted to account for the possibility that if a was. Less than b, we could say a is not larger than b, right. And that would work. However, there's a better way to do that than to just do a series of if statements one after the other and we're going to see how to do that in the next movie.

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This video is part of

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PHP with MySQL Essential Training

131 video lessons · 34408 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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