Method Arguments

7:02 with Jay McGavren

A parameter is a special variable that you declare at the start of a method. When a method takes parameters, you need to provide argument values when calling that method. Ruby sets each parameter variable with the value in the argument.

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We still can't specify how many seconds our wait method should pause for.
But learning about variables was an important step. Now let's learn about the last piece of the puzzle: method parameters.
A parameter is a special variable that you declare at the start of a method.
- This method takes two parameters, one named first and one named second:

def add(first, second)
  puts first, second
  puts first + second
end

When a method takes parameters, you need to provide argument values when calling that method.
- Ruby sets each parameter variable with the value in the argument.

def add(first, second)
  puts first, second
  puts first + second
end

def subtract(first, second)
  puts first, second
  puts first - second
end

add(100, 50) # 150
subtract(75, 25) # 50
add(3, 4) # 7
subtract(10, 5) # 5

Here's our wait method from before, updated with a parameter for the number of seconds it should wait:

def wait(seconds)
  puts "Waiting..."
  sleep seconds
  puts "Done"
end

wait 1
wait 3

0:00
We still aren't able to specify how many seconds our wait method should pause for.
0:04
But learning about variables was an important step.
0:07
Now let's learn about the last piece of the puzzle, method parameters.
0:12
A parameter is a special variable that you declare at the start of a method.
0:16
Let's start a new file, so that we can experiment with method parameters.
0:23
So we'll name it parameters.rb.
0:25
A parameter is a special variable that you declare at the start of our method.
0:30
So let's define a new method named add that takes two parameters.
0:35
Parameters are included within parentheses following the method name.
0:39
So we're going to define our ad method to take one parameter named first.
0:44
And this is basically just an ordinary variable, so
0:47
it follows all the same naming conventions as variables.
0:51
Then we'll add a second parameter that will hold the number that should be added
0:54
to the first number.
0:55
We separate parameters with commas.
0:57
So I'll type a comma and a space and
0:59
then my second parameter which I'll choose to name second.
1:03
Method definitions end with the keyword end.
1:06
So I'll go ahead and type that first.
1:09
And now that we've declared these parameter variables,
1:11
we can use them within the method body.
1:13
So let's add a couple snippets of code that use these parameters.
1:17
First I'll make a call to put S and pass it the first and
1:22
second parameters just to print out what we received as parameters.
1:27
And then I'll call puts again.
1:28
And I'll pass it the result of adding the value in the first parameter to
1:32
the value in the second parameter.
1:35
We'll be talking more about math operations like this one in an upcoming
1:39
stage.
1:40
Now, let's define a second method named subtract.
1:46
And this is also going to take a couple parameters.
1:49
We'll use the same names as we did before.
1:52
Just by choice we could change them to different names, but
1:56
it's okay if we repeat them, too.
1:58
So we'll name them first and second.
2:03
Method definition should end with the keyword end.
2:06
And as before, we'll call puts and pass it the first and second parameters.
2:12
And we'll also call puts again,
2:14
with the result of subtracting the second parameter from the first parameter.
2:20
When you've define a method to take parameters,
2:23
you need to provide argument values when calling that method.
2:27
Ruby sets each parameter value with the value in the argument.
2:31
So let's try making a call to our add method.
2:35
And we need to provide arguments to that method here in parenthesis following
2:39
the method name.
2:40
Just like before, we need to separate our arguments with comas.
2:43
I'm going to call the add the method and I'll set the first parameter,
2:49
the parameter named first up here, to the value 100.
2:53
And I'll set the second parameter, the parameter named second to the value 50.
3:00
Ruby will take the first argument to the method call and
3:03
set the first parameter to that value.
3:06
It'll take the second argument to the method call and
3:09
set the second parameter to that value.
3:13
Let's save this and try running it.
3:16
So we'll say ruby space parameters.rb.
3:24
Our code calls the add method with arguments of 100 and 50.
3:28
The first parameter get set to 100.
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The second parameter get set to 50.
3:35
And first within our method body,
3:37
it calls the puts method with the first and second parameters as arguments.
3:42
It prints out our 2 arguments, 100 and 50.
3:45
Then this line of code calls the puts
3:48
method with the result of adding the first and second parameters.
3:52
So 100 gets added to 50 with the result 150 and that is what gets printed out.
3:58
Now, let's try adding a call to our subtracts method.
4:01
We a typed a method names subtract parenthesis for our arguments.
4:06
And we'll set our first argument to 75 and we'll set our second argument to 25.
4:13
Try running that.
4:18
And here you can see the results of the add call him down
4:21
here you can see the results of the subtract call.
4:25
It prints out its 2 arguments, first and second 75 and 25.
4:29
And then it prints the result of subtracting 25 from 75 which is 50.
4:35
And we can pass different arguments each time we call a method.
4:39
So let's try calling the add method again and
4:41
this time we'll use arguments of 3 and 4.
4:44
We'll also make another call to subtract.
4:47
And we'll give it arguments of 10 and 5.
4:52
Save that, run it.
4:55
And here you can see the results of our second call to the add method.
4:58
It prints out its arguments of 3 and 4,
5:01
plus the results of adding them which is 7.
5:05
And here you can see our second call to subtract.
5:07
It prints out the arguments of 10 and
5:09
5 and the result\ of subtracting them which is 5.
5:13
And again, as with all other method calls, parentheses are optional.
5:17
If we wanted, we could remove the parentheses up here, and
5:20
the code will work exactly the same way.
5:22
So I'll replace the opening parenthesis with spaces.
5:25
I'll delete the closing parentheses, save this, and try re-running it.
5:31
And you can see that the code works just the same as before.
5:34
Now that we understand Ruby parameters and arguments a bit better,
5:38
we're ready to update our wait method to take a variable number of seconds to wait.
5:43
So let's close out of our parameters.rv file and go back to our temp.rv file.
5:48
We're going to go up to the definition of the wait method.
5:52
And we're going to type in a parameter that it should accept.
5:56
We'll name it seconds, as in the number of seconds that it should wait for.
6:01
That should go here in parentheses following the method name.
6:04
And that parameter becomes a variable that can be used within our method body.
6:08
So in place of always sleeping for three seconds down here,
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we're going to sleep for whatever value the seconds variable contains.
6:17
With that parameter added to the method definition,
6:19
we can now go down here to the call to wait and add an argument to that method.
6:25
We'll go ahead and skip the parentheses this time.
6:27
And for my first call to wait, I'm going to wait just 1 second.
6:30
I'l add another call to wait where I wait for 3 seconds.
6:34
Let's go down here to the console and try running it.
6:38
Ruby space temp.rb.
6:41
And you see that it says waiting with a brief pause and
6:46
then waiting again with much longer pause.
6:50
And those pauses are 1 and 3 seconds specifically because that's how
6:55
long we specified in our arguments to the wait method.

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Ruby Basics

Method Arguments

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