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Method Arguments

Name: Method Arguments
Uploaded: 2017-08-27T17:33:44-04:00
Duration: 422 s
Description: 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.

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

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We still aren't able to specify how many seconds our wait method should pause for. 0:00

But learning about variables was an important step. 0:04

Now let's learn about the last piece of the puzzle, method parameters. 0:07

A parameter is a special variable that you declare at the start of a method. 0:12

Let's start a new file, so that we can experiment with method parameters. 0:16

So we'll name it parameters.rb. 0:23

A parameter is a special variable that you declare at the start of our method. 0:25

So let's define a new method named add that takes two parameters. 0:30

Parameters are included within parentheses following the method name. 0:35

So we're going to define our add method to take one parameter named first. 0:39

And this is basically just an ordinary variable, so 0:44

it follows all the same naming conventions as variables. 0:47

Then we'll add a second parameter that will hold the number that should be added 0:51

to the first number. 0:54

We separate parameters with commas. 0:55

So I'll type a comma and a space and 0:57

then my second parameter which I'll choose to name second. 0:59

Method definitions end with the keyword end. 1:03

So I'll go ahead and type that first. 1:06

And now that we've declared these parameter variables, 1:09

we can use them within the method body. 1:11

So let's add a couple snippets of code that use these parameters. 1:13

First I'll make a call to put S and pass it the first and 1:17

second parameters just to print out what we received as parameters. 1:22

And then I'll call puts again. 1:27

And I'll pass it the result of adding the value in the first parameter to 1:28

the value in the second parameter. 1:32

We'll be talking more about math operations like this one in an upcoming 1:35

stage. 1:39

Now, let's define a second method named subtract. 1:40

And this is also going to take a couple parameters. 1:46

We'll use the same names as we did before. 1:49

Just by choice we could change them to different names, but 1:52

it's okay if we repeat them, too. 1:56

So we'll name them first and second. 1:58

Method definition should end with the keyword end. 2:03

And as before, we'll call puts and pass it the first and second parameters. 2:06

And we'll also call puts again, 2:12

with the result of subtracting the second parameter from the first parameter. 2:14

When you've define a method to take parameters, 2:20

you need to provide argument values when calling that method. 2:23

Ruby sets each parameter value with the value in the argument. 2:27

So let's try making a call to our add method. 2:31

And we need to provide arguments to that method here in parentheses following 2:35

the method name. 2:39

Just like before, we need to separate our arguments with comas. 2:40

I'm going to call the add the method and I'll set the first parameter, 2:43

the parameter named first up here, to the value 100. 2:49

And I'll set the second parameter, the parameter named second to the value 50. 2:53

Ruby will take the first argument to the method call and 3:00

set the first parameter to that value. 3:03

It'll take the second argument to the method call and 3:06

set the second parameter to that value. 3:09

Let's save this and try running it. 3:13

So we'll say ruby space parameters.rb. 3:16

Our code calls the add method with arguments of 100 and 50. 3:24

The first parameter get set to 100. 3:28

The second parameter get set to 50. 3:31

And first within our method body, 3:35

it calls the puts method with the first and second parameters as arguments. 3:37

It prints out our 2 arguments, 100 and 50. 3:42

Then this line of code calls the puts 3:45

method with the result of adding the first and second parameters. 3:48

So 100 gets added to 50 with the result 150 and that is what gets printed out. 3:52

Now, let's try adding a call to our subtracts method. 3:58

We typed a method named subtract, parentheses for our arguments. 4:01

And we'll set our first argument to 75 and we'll set our second argument to 25. 4:06

Try running that. 4:13

And here you can see the results of the add called down 4:18

here you can see the results of the subtract call. 4:21

It prints out its 2 arguments, first and second 75 and 25. 4:25

And then it prints the result of subtracting 25 from 75 which is 50. 4:29

And we can pass different arguments each time we call a method. 4:35

So let's try calling the add method again and 4:39

this time we'll use arguments of 3 and 4. 4:41

We'll also make another call to subtract. 4:44

And we'll give it arguments of 10 and 5. 4:47

Save that, run it. 4:52

And here you can see the results of our second call to the add method. 4:55

It prints out its arguments of 3 and 4, 4:58

plus the results of adding them which is 7. 5:01

And here you can see our second call to subtract. 5:05

It prints out the arguments of 10 and 5:07

5 and the result of subtracting them which is 5. 5:09

And again, as with all other method calls, parentheses are optional. 5:13

If we wanted, we could remove the parentheses up here, and 5:17

the code will work exactly the same way. 5:20

So I'll replace the opening parenthesis with spaces. 5:22

I'll delete the closing parentheses, save this, and try re-running it. 5:25

And you can see that the code works just the same as before. 5:31

Now that we understand Ruby parameters and arguments a bit better, 5:34

we're ready to update our wait method to take a variable number of seconds to wait. 5:38

So let's close out of our parameters.rb file and go back to our temp.rb file. 5:43

We're going to go up to the definition of the wait method. 5:48

And we're going to type in a parameter that it should accept. 5:52

We'll name it seconds, as in the number of seconds that it should wait for. 5:56

That should go here in parentheses following the method name. 6:01

And that parameter becomes a variable that can be used within our method body. 6:04

So in place of always sleeping for three seconds down here, 6:08

we're going to sleep for whatever value the seconds variable contains. 6:12

With that parameter added to the method definition, 6:17

we can now go down here to the call to wait and add an argument to that method. 6:19

We'll go ahead and skip the parentheses this time. 6:25

And for my first call to wait, I'm going to wait just 1 second. 6:27

I'l add another call to wait where I wait for 3 seconds. 6:30

Let's go down here to the console and try running it. 6:34

Ruby space temp.rb. 6:38

And you see that it says waiting with a brief pause and 6:41

then waiting again with much longer pause. 6:46

And those pauses are 1 and 3 seconds specifically because that's how 6:50

long we specified in our arguments to the wait method. 6:55

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Ruby Basics

Method Arguments

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