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Logical Operators
6:39If we want to check for multiple conditions at once, we can combine conditional statements using logical operators. In this video, we'll use logical operators to combine the nested if statements from the last video.
Documentation
Logical Operators allow you to combine conditional statements in the same way that you would combine phrases in a sentences. "My favorite colors are red AND purple"
XOR Operator
PHP also includes an operator called XOR, meaning "Exclusive OR". XOR checks two conditions and returns TRUE if EITHER of the conditions are true, but not both.
Let's look at an example of XOR.
if ($num == 10 XOR is_string($num)) {
echo '10 or string, but not the string "10"';
} else {
echo 'Either the string "10" or NOT 10 and NOT string';
}
Using OR evaluates to true when both expressions are true but XOR evaluates to false when both expressions are true.
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In the last video,
0:00
we nested conditional statements
to compare more than one equation.
0:01
If we want to check for
multiple equations at once,
0:05
we can combine conditional
statements using logical operators.
0:09
Logical operators allow you to
combine conditional statements
0:13
in the same way that you would
combine phrases in a sentence.
0:17
My favorite colors are red and purple.
0:20
Let's use logical operators to combine the
nested if statement from the last video.
0:24
Let's duplicate this code and
save the example in the comments.
0:29
Now we have two if statements.
0:41
If num >= 10 and
0:44
if num <= 1000.
0:47
Let's combine these statements
using the logical operators for
0:51
AND, a double ampersand.
0:56
Now we're going to use just two displays.
1:03
Either your number's within the range or
1:05
your number is not within the range.
1:09
Let's run the script.
1:18
Your number is NOT within the range.
1:21
If I change this to 10 Your
number is within the range.
1:23
If I change this to 10,000
1:31
We see your number is NOT
within the range again.
1:39
By using the logical operator for
AND, we require that both equations
1:43
must evaluate as true for
this conditional to evaluate as true.
1:48
This combined statement clearly
defines our requirements.
1:53
We want to know if a value
falls within a range.
1:57
We are not trying to evaluate for
less than 10 or greater than 1,000.
2:00
We only want to evaluate whether
the number falls within the range.
2:04
Let's comment out this conditional and
try an OR.
2:09
Using OR means that only one
equation must evaluate as true but
2:17
both may evaluate as true.
2:22
Let's show an example of OR
using the double pipes to represent OR.
2:25
If ($num == 10 ||
2:29
is_string ($num)) {.
2:35
Echo '10 or string'; Else,
2:42
echo "NOT 10 or string".
2:48
The is string function does
just what it sounds like.
2:57
It checks if the variable
given is a string.
3:00
I'll add a link in the teacher's notes for
more information.
3:04
Let's set num equal to the integer 10.
3:07
Now let's run our script.
3:10
We see 10 or string.
3:15
Now let's change num to the string 10.
3:18
Again we see 10 or string.
3:24
And if we change this to the string
20 we also see 10 or string.
3:27
Because 20 in quotes is a string.
3:38
And finally, if we change num to equal
the integer 20, we see not 10 or string.
3:42
As I've shown you, using or
evaluates to true when one or
3:52
both expressions are true.
3:57
When both expressions are false,
the entire conditional evaluates to false.
3:59
There are two different ways to write AND
and OR.
4:05
I demonstrated the most common use first.
4:08
The double ampersand for AND
and the double pipes for OR.
4:11
You can also use the keywords AND
and OR as the operators themselves.
4:16
Most of the time you won't
see any difference in
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the performance of these operators.
4:25
The difference lies in the precedence
which expression will get evaluated first.
4:27
The special operators double ampersand and
double pipe,
4:32
are used most often because they
have the highest precedence.
4:35
To see this in more detail
check out the teacher's notes.
4:40
But let me show you a quick example
of what this actually means.
4:42
Let's comment out our last conditional and
move to the end of the file.
4:47
Let's add $var1 =
4:56
true && false.
5:01
$var2 equal true and false.
5:07
Now we can var_dump ($var1, $var2).
5:15
We can dump more than one value in a
single var_dump statement using the comma.
5:24
Now when we run the script,
we see that var1 evaluates to false,
5:28
while var2 evaluates to true.
5:34
This is because the double ampersand
has a higher precedence than equal.
5:37
So true and false is evaluated first,
which evaluates to false.
5:42
And then that false value
is assigned to var1.
5:46
It acts as if parentheses were
added around the true and false.
5:50
The second statement evaluates to true,
5:56
because the equal sign has a higher
precedence than the and keyword.
5:59
So true is assigned to var2
before it's compared to false.
6:04
The second statement works as if there
were parentheses around var2 equals true.
6:08
Great work learning to express
yourself through code.
6:18
By using specific comparison operators
along with logical operators, your
6:21
code can not only solve a problem, but clearly define which problem it's solving.
6:26
This makes your code easier and
more enjoyable to read.
6:31
It also becomes easier to make changes or
add features in the future.
6:35