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One great power of any programming language is the ability to evaluate data and take action based off of that data using conditional statements. We'll connect the concepts of conditionals that we use everyday with the syntax used in PHP.
If Statements are one of the most important features of many languages, PHP included. It allows for conditional execution of code fragments. The expression is evaluated to its Boolean value. If expression evaluates to TRUE, PHP will execute statement, and if it evaluates to FALSE - it will ignore the statement.
Example
$a = 10;
$b = 5;
if ($a > $b) {
echo "a is bigger than b";
}
Will display "a is bigger than b" because 10 is greater than 5.
Note: when you only have a single statement, you MAY leave off the curly braces. Example:
if ($a > $b)
echo "a is bigger than b";
elseif, as its name suggests, is a combination of if and else. Like else, it extends an if statement to execute a different statement in case the original if expression evaluates to FALSE. However, unlike else, it will execute that alternative expression only if the elseif conditional expression evaluates to TRUE.
Example
$a = 10;
$b = 10;
if ($a > $b) {
echo "a is bigger than b";
} elseif ($a == $b) {
echo "a is equal to b";
} else {
echo "a is smaller than b";
}
Will display "a is equal to b" because 10 equals 10. Only a single expression block will be executed
One great power of any
programming language
0:00
is the ability to evaluate data and
take action based off that data.
0:02
For example, if you're logged in to
treehouse, you can take these courses.
0:07
But if you're not logged in
you'll be directed to sign up.
0:11
We evaluate the data,
your logged in status, and
0:15
take different actions based on that data.
0:17
We evaluate and take actions on data
by using conditional statements.
0:20
The most basic conditional
is called an if statement.
0:25
We use the concept of an IF
statement all the time.
0:29
For example, if the time is six AM,
my alarm will sound to wake me up.
0:32
Or if it's Wednesday at three PM,
I need to be in a meeting.
0:36
If we're hungry, we should eat.
0:40
If we're tired, we should sleep.
0:42
If it's dark, we need to turn on a light.
0:44
This is the same with programming.
0:46
If something is true,
then we want to perform some action,
0:48
if not,
then we're going to skip over that action.
0:52
In the last video,
we learned to compare values and
0:55
return a true false result
using the comparison operators.
0:59
We use those comparison results for
our conditional.
1:03
If the comparison is true
then perform some action.
1:06
Let's get started with
our first conditional.
1:10
We already have the var_dump of
our comparison of string one,
1:13
and we know that it evaluates to true.
1:17
So let's comment out this
display of string one.
1:20
Then we can duplicate this line and
1:22
comment out the first one, and
we'll change this to be an if statement.
1:27
If, just like with the vardump,
1:33
the condition that we are testing
goes within parentheses.
1:36
But instead of finishing this
statement with the semi colon,
1:40
we use curly braces to surround
the action we're going to perform.
1:43
In this case, I'm going to echo
>> The values match.
1:50
So if string one equals the string
we are comparing it to,
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which we already know that it does,
2:01
we're going to perform the action within
the curly braces of our IF statement.
2:03
In this case echo the values match.
2:08
So let's run our script.
2:11
Great!
We see the values match.
2:14
Let's change our strings slightly so
that it doesn't match.
2:16
And now run the script again.
2:23
This time we don't see anything.
2:26
That's because our conditional
now evaluates to false.
2:28
So it skips the action
within the curly braces.
2:32
What if instead of just skipping over the
action, we want to perform another action.
2:35
Like telling the user that
the values are not equal.
2:40
We can add an l statement
to this conditional.
2:43
After the closing curly braces,
we add else.
2:46
And then another set of curly braces.
2:51
Now if the condition is true,
we perform the action in the first set
2:55
of curly braces, and
the else statement is ignored altogether.
2:58
If the conditional is false,
we skip the first set of curly braces and
3:03
perform the action in
the second set of curly braces.
3:07
So let's echo the values do not match.
3:10
And let's run our script again.
3:16
We see the values do not match,
because only one set of
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actions will be performed
the statement is either true or false.
3:26
Either the values match or
the values do not match.
3:30
There is one more way that we
can extend this if statement.
3:34
We combine if and else to test for
a second condition.
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Before this else statement,
we can add an else if.
3:44
Again, we'll want an opening and
closing curly brace.
3:53
For this conditional, let's check
if $string_one is an empty string.
3:57
We'll add, in parentheses,
$string_one Equals an empty string.
4:02
If this statement is true and
the string_one is an empty string,
4:11
let's echo '$string_one is empty';.
4:15
Because the variable is
within single quotes,
4:24
we will see the variable
name instead of the value.
4:26
So first we test if string one
is equal to a specific string.
4:30
If that conditional is true,
we display the values match, and
4:34
the entire IF statement is complete.
4:38
If that conditional is false, we continue
on to our next else if condition
4:40
that tests if string
one is an empty string.
4:46
If this condition is true we display,
string one is empty, and
4:49
the if statement is now complete.
4:53
Finally, if both of those
conditions are false,
4:56
we reach our else statement which
displays, the values do not match.
4:59
Again only one action will be performed
5:04
even though we now have
three actions available.
5:07
Let's test this out by running our code.
5:10
We see the values do not match.
5:14
Since the variable does not match
the string in the first conditional, and
5:16
it also is not an empty string, we are
executing the code within the else block.
5:20
Let's change our string back to match and
run the script again.
5:26
This time we see the values match,
because our first conditional is true, and
5:33
we don't even attempt to reach
the other statement blocks.
5:37
Finally, let's reset
the string one variable.
5:41
We'll set string one
equal to an empty string.
5:43
Now let's run the script again,
and we see string one is empty.
5:51
The first conditional was false, so
5:56
it moved on to the second conditional,
which evaluated to true.
5:59
So the code inside the second
code block was executed and
6:03
the if statement is complete,
it does not look at the final else block.
6:06
Great job working through
those conditionals.
6:12
If you'd like to review conditionals,
feel free to rewatch the video.
6:14
Else you can continue on to the next video
6:19
where we'll be creating our
daily exercise program.
6:22
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