Negation Operator

One of the goals we should have when writing code 0:00 is to clearly define what our code should be doing. 0:03 In light of this goal, sometimes we don't need to compare if something is equal, but 0:06 rather we need to compare if something is not equal. 0:11 As an example, if a user is not logged in, 0:15 we want to redirect them to a login screen. 0:18 We check for nonequality by using negation operators. 0:21 Let's not just talk about them, let's start using these negation operators. 0:25 There are many different ways to check for nonequality. 0:31 We've actually already done this with our first else statement. 0:34 Let's comment out our code from score and add the first else statement. 0:37 If ($a == $b), 0:48 echo 'values are equal'. 0:54 Else echo 'values are NOT equal'. 1:02 If we only want to do something if an expression is not true, 1:13 such as redirect to a login in page if the user is not logged in. 1:16 We can just leave off the action in the first block. 1:21 This can be confusing, hard to read and extra code. 1:26 We could also compare an expression to false. 1:29 Let's duplicate this and add parentheses and 1:35 a condition and then say == false. 1:41 Now we can remove this else. 1:49 This at least removes our need for an empty code block and the extra else, but 1:51 it hasn't made the code really any easier to read. 1:56 If anything, it's made it more complicated. 1:59 This is where a negation operators can clarify your code and 2:02 make it easier to read. 2:05 Let's duplicate this line. 2:07 And this time. 2:13 We'll use a negation operator. 2:19 To start with, if you want to check if something is less than or greater than 2:22 a value, you can combine those two operators, less than or greater than. 2:26 Essentially this tests if a is not equal to b, 2:31 because a is either less than or greater than b. 2:36 Let's run this in the console again. 2:40 We see that the values are not equal. 2:45 The values are not equal. 2:47 Values are not equal three times. 2:48 Less than or greater than doesn't make sense when comparing strings. 2:51 Fortunately PHP also provides a negation operator, the exclamation point. 2:55 This is typically what you'll see used when checking for a negative value, 3:01 because it works no matter which type of values you're comparing. 3:05 Let's create a new conditional, and comment out the rest of these. 3:09 Okay, if a is not equal to b. 3:20 Now we can run the script, and we see that the values are not equal. 3:26 Notice I use a single equal after the exclamation point. 3:31 This means that the values of a and b are not equal. 3:34 This does not compare the variable types, just the values. 3:39 So if I change the value of a to be the string five, and run the script again, 3:42 I get no output because the string five is still equal to the integer five. 3:52 If I wanted to check for 3:59 the type as well, I can use a double equal after the exclamation point. 4:00 Let's change this to not identical. 4:09 Now when I run the script, I see NOT identical because 4:18 the string a is not identical to the integer a. 4:24 They're of different types. 4:29 Let's comment out these conditionals and try something else. 4:31 Conditional statements evaluate the value of the given data as either true or false. 4:36 In these examples, we've been comparing two variables as either true or false. 4:42 But any single variable or value can be evaluated as true or false as well. 4:47 I'll add the link in the teacher's notes, where we explore this in more depth. 4:53 For now, let's just say if a echo true. 4:57 When we run the script, we see true. 5:04 Because the value 5 evaluates to true. 5:10 If I change the value of a to equal 0 and 5:14 run the script again, we no longer see true, 5:20 because like most programming languages PHP treats the integer 0 as false. 5:23 When I duplicate this statement. 5:30 And change it to NOT a, this would be false. 5:34 Now I can run my statement and see false, because a does not evaluate to true. 5:43 A evaluates to false, which is the value we're looking for in our conditional. 5:50 I could also write this another way. 5:55 I could do a is equal 5:58 to false. Or even 6:03 A is not equal to true. 6:11 Now when I run the script, I see false three times, 6:15 because I'm comparing the value of a to the boolean true or false, 6:23 PHP juggles the value of a to b, either true or false. 6:28 You can see more about type juggling in the teacher's notes. 6:33 In this video, I demonstrated many different ways to get the same answer. 6:37 You should choose the option that most clearly expresses your intent. 6:42 You'll hear me repeat this many times. 6:46 Making your code easy to read is a great benefit for others and for 6:49 your future self. 6:53 It's been estimated that 80% of the developers' time is spent reading code. 6:55 So code that's easy to read helps you be more productive and 7:00 makes your day much more enjoyable. 7:04 Choose operators that clearly model your requirements. 7:07 If you need to check if a user is not logged in, use a negation operator. 7:10 If you're looking for score of 60 or greater, 7:15 don't just use greater than 59, use greater than or equal to 60. 7:19 If you need to compare the variables as identical and not just equal in value, 7:24 meaning that the types match as well as the values, use the triple equal. 7:29 By clearly expressing the requirements of your program, you make your conditionals 7:34 and thereby your code as a whole easier and more enjoyable to read. 7:38