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Sometimes if an argument is not passed through, and you want it to have a starting value, no matter what, this is where a default argument will come to your assistance.
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Having a good understanding of what a
function argument means,
0:01
we can now talk about another important
component known as default arguments.
0:03
Sometimes, if an argument is not passed
through, but
0:08
you want the function to have a starting
value no matter what,
0:11
this is where a default argument will come
to your assistance.
0:15
Now you can see it's just hello, dollar
sign, name.
0:18
Then, we'll simply add name equals and
0:22
then whatever our definition for the
default argument should be.
0:26
In this case we'll just do friend that way
I can pass through an argument like this.
0:30
So I'll say hello and then Mike.
0:34
That way it'll say Hi, Mike, how's it
going?
0:37
But if I choose to just pass through
hello,
0:40
remember we didn't define anything outside
of the function scope like before, but
0:43
now it's gonna say Hi, friend, how's it
going?
0:47
Now what if we wanted to do multiple
default arguments,
0:50
just like in our greet function?
0:54
We'll simply add the same way we did it
before, which is equals friend and
0:55
then equals morning on time_of_day and
name, respectively.
1:00
This way I can still call, greet Mike
afternoon and
1:04
get, Hi, Mike, good afternoon.
1:08
But if I pass with no arguments
whatsoever, it'll just say, Hi, friend,
1:11
good morning.
1:16
Now let's say we wanted to make an
argument predefined as optional.
1:17
Well the way we do that is in the same way
we've done default arguments.
1:22
Let's say for instance, I don't really
need you to provide me a time of day.
1:26
Well, let's do that by simply eliminating
it set to morning and
1:30
make it equal to Null.
1:35
This way, we have to check inside the
function if time of day is set.
1:37
So we'll check if time_of_day, and
1:42
then we'll surround our previous statement
with an if and an else.
1:44
Now, if time_of_day is equal something
other than null,
1:49
it'll say hi name and then good
time_of_day.
1:52
But we need to provide an else as well.
1:56
So what we'll do is just say echo hello
comma name.
1:59
And close that statement with a semicolon.
2:04
This way I can still say greet Mike
afternoon and get, Hi, Mike,
2:07
good afternoon.
2:12
But I'm also able to just pass through
Mike to our
2:13
greet function without the time of day and
we'll end up getting this back.
2:16
Hi, Mike.
2:20
So now let's talk a look here in
Workspaces on how to
2:22
work with default arguments.
2:25
So far we have had some arguments here,
we've passed through arguments,
2:27
if we don't pass an argument we'll end up
getting an error.
2:32
So what we'll need to do is create default
arguments so
2:35
that way we don't get the errors when we
forget to pass through.
2:38
We'll also look at how to make arguments
optional.
2:42
So, let's start with creating a function
that will show a little
2:45
bit of info about someone and maybe who
they are or a title.
2:48
So let's start with creating that
function.
2:53
So function and then get info.
2:56
'Kay.
And we're gonna have two argument here,
3:01
one is gonna be the name and next one is
going to be the title.
3:03
'Kay?
3:07
Then open and close our curly braces.
3:09
So now we have our function.
3:12
Now inside of this function what we want
to do is just echo a string.
3:14
So echo, and then we'll go ahead and
3:17
do double quotes even though we're going
to output some variable information.
3:20
So let's start with name and then has
arrived,
3:26
they are with us as a and then title.
3:32
So this way in a string format if I was to
say get info.
3:38
And then pass through two strings.
3:45
So let's say Mike and Mike is a frog.
3:46
Okay.
So we have multiple arguments here and
3:51
we have one is the name and next will be
in the title.
3:54
So notice they are in the same order as
they were defined on line three.
3:58
So I'm going to go ahead and save this and
then take out, take a look at the preview.
4:01
So here we see it says Mike has arrived.
4:06
They are with us as a frog.
4:09
Okay.
That seems perfectly reasonable.
4:11
Let's go back over and say that we forget
to type in frog.
4:13
We just save this and hit refresh.
4:19
It'll say Mike has arrived.
4:21
They are with us as a, nothing.
4:22
There's a blank.
4:25
Well we don't want that so
4:25
we're gonna need to define some kind of
default argument here.
4:27
So let's go back over to our code and then
say, get info, title, and name.
4:31
Well let's say we want to define a title
to start with so
4:37
we say title equals, and this is where our
default is.
4:41
And we'll say, friend.
4:45
All right, now save it.
4:46
And if we don't use title as an argument
it should come through as friend.
4:50
So we'll go ahead and hit our Preview.
4:55
Refresh.
4:58
And there it says, Mike has arrived, they
with us as a friend.
4:59
Which is great.
5:02
Okay.
5:03
Now what if we wanted to take, and make
the title completely optional?
5:04
Well, that's pretty easy to do.
5:09
All we need to do is remove equals friend,
and just simply say equals null.
5:12
Okay, this way it's not gonna report back
any kind of errors or notices for us.
5:17
But we need to do something a little
different.
5:23
Cuz otherwise, it's just gonna come up
with that blank again.
5:24
So let's create an if statement to test
whether or not title exists.
5:27
So we'll say if, and then we'll say title.
5:31
We don't need to see if it's true or
anything like that.
5:36
Just simply saying if title, make sure
that it exists.
5:38
It's anything other than null.
5:41
All right.
So if title.
5:43
We're gonna open and close our curly
braces, oh and then else.
5:45
We're going to do something different.
5:48
All right.
5:50
Well I'm actually going to actually use
this line.
5:51
So, I'm gonna cut it, and then head back
up here and paste it in.
5:53
Make sure my tabs are good.
5:57
Okay.
5:58
And then here if we don't have a title, we
want to echo something different.
5:59
So, echo and then name has arrived, and
then welcome.
6:02
Perfect, all right.
6:10
So now we close that with a semicolon to
end our statement.
6:12
So if we go down and
6:17
run what we have currently by going to our
preview button and refreshing it.
6:18
Now it says, Mike has arrived, welcome.
6:22
Because on line 13 here we did not pass
through an argument.
6:24
But if we do pass through an argument here
such as let's say, frog.
6:29
Save it.
6:36
And then refresh our preview.
6:36
Now it will say, Mike has arrived, they
are with us as a frog.
6:39
So, in order to get a optional argument we
can simply
6:42
pass through the default argument as null,
or we can pass through a string or
6:45
any kind of value we want to use as our
default argument
6:50
in the argument definition of the function
such as in line three.
6:54
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