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One of the goals we should
have when writing code

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is to clearly define what
our code should be doing.

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In light of this goal, sometimes we don't
need to compare if something is equal, but

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rather we need to compare
if something is not equal.

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As an example, if a user is not logged in,

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we want to redirect
them to a login screen.

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We check for
nonequality by using negation operators.

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Let's not just talk about them, let's
start using these negation operators.

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There are many different ways to check for
nonequality.

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We've actually already done this
with our first else statement.

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Let's comment out our code from score and
add the first else statement.

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If ($a == $b),

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echo 'values are equal'.

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Else echo 'values are NOT equal'.

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If we only want to do something
if an expression is not true,

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such as redirect to a login in
page if the user is not logged in.

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We can just leave off
the action in the first block.

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This can be confusing,
hard to read and extra code.

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We could also compare
an expression to false.

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Let's duplicate this and
add parentheses and

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a condition and then say == false.

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Now we can remove this else.

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This at least removes our need for an
empty code block and the extra else, but

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it hasn't made the code
really any easier to read.

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If anything,
it's made it more complicated.

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This is where a negation operators
can clarify your code and

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make it easier to read.

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Let's duplicate this line.

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And this time.

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We'll use a negation operator.

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To start with, if you want to check if
something is less than or greater than

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a value, you can combine those two
operators, less than or greater than.

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Essentially this tests
if a is not equal to b,

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because a is either less than or
greater than b.

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Let's run this in the console again.

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We see that the values are not equal.

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The values are not equal.

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Values are not equal three times.

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Less than or greater than doesn't
make sense when comparing strings.

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Fortunately PHP also provides a negation
operator, the exclamation point.

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This is typically what you'll see used
when checking for a negative value,

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because it works no matter which
type of values you're comparing.

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Let's create a new conditional,
and comment out the rest of these.

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Okay, if a is not equal to b.

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Now we can run the script, and
we see that the values are not equal.

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Notice I use a single equal
after the exclamation point.

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This means that the values of a and
b are not equal.

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This does not compare the variable types,
just the values.

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So if I change the value of a to be
the string five, and run the script again,

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I get no output because the string five
is still equal to the integer five.

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If I wanted to check for

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the type as well, I can use a double
equal after the exclamation point.

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Let's change this to not identical.

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Now when I run the script,
I see NOT identical because

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the string a is not
identical to the integer a.

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They're of different types.

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Let's comment out these conditionals and
try something else.

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Conditional statements evaluate the value
of the given data as either true or false.

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In these examples, we've been comparing
two variables as either true or false.

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But any single variable or value can
be evaluated as true or false as well.

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I'll add the link in the teacher's notes,
where we explore this in more depth.

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For now, let's just say if a echo true.

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When we run the script, we see true.

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Because the value 5 evaluates to true.

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If I change the value of a to equal 0 and

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run the script again,
we no longer see true,

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because like most programming languages
PHP treats the integer 0 as false.

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When I duplicate this statement.

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And change it to NOT a,
this would be false.

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Now I can run my statement and see false,
because a does not evaluate to true.

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A evaluates to false, which is the value
we're looking for in our conditional.

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I could also write this another way.

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I could do a is equal

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to false. Or even

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A is not equal to true.

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Now when I run the script,
I see false three times,

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because I'm comparing the value of
a to the boolean true or false,

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PHP juggles the value of a to b,
either true or false.

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You can see more about type
juggling in the teacher's notes.

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In this video, I demonstrated many
different ways to get the same answer.

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You should choose the option that most
clearly expresses your intent.

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You'll hear me repeat this many times.

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Making your code easy to read is
a great benefit for others and for

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your future self.

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It's been estimated that 80% of the
developers' time is spent reading code.

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So code that's easy to read
helps you be more productive and

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makes your day much more enjoyable.

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Choose operators that clearly
model your requirements.

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If you need to check if a user is not
logged in, use a negation operator.

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If you're looking for
score of 60 or greater,

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don't just use greater than 59,
use greater than or equal to 60.

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If you need to compare the variables as
identical and not just equal in value,

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meaning that the types match as well
as the values, use the triple equal.

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By clearly expressing the requirements of
your program, you make your conditionals

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and thereby your code as a whole
easier and more enjoyable to read.