Methods and Parameters
Last updated
Last updated
Writing methods allows us to break our code into well-organized and reusable parts. But sometimes we may want to reuse a method with a slight change.
Take a look at the following code:
Notice that the code contains some repetition. The process of adding 10 to a variable is the same whether we're adding 10 + 3 or 10 + 21. In each case, we're adding 10.
Recall that methods are like blocks of code that do a particular thing. We can write a method that prints out "hello" when called, or a method that draws a circle. But what if we want to create a method to add ten to a number? We can sketch out the method like so:
We would expect an addTen method to add 10 to any number it is given. If we give it 3, the method will give us 13. Were we to give it 32, it would give us 42. This pattern can be generalized even more: if we give the method any number x, it will give us x + 10 in return. The action that the addTen method takes is the same every time -- it adds 10 -- the only thing that changes is the number we give to the method. The number that we pass to the method is called a parameter.
Let's write the addTen method in code:
Notice that there is an x that is being taken in and used by the method. This is the parameter. Its value will be whatever the user decides to "pass" to the method. Also note that the x parameter can be used like a regular variable in the body of the method.
Now that the addTen method is defined, it's time to call the method. Let's first add ten to the number 5:
This will result in 15 being printed to the console.
This works with variables as well. We can create a variable y that stores a number, then pass y to the addTen method:
The variable 115 is passed as an argument to the addTen method. The method accepts 115 as the parameter, adds 10 to it, and then prints 125 to the console.
It's often helpful to write methods that can take in more than one parameter. For example, if we were to write a generic add method, we would want to be able to input two numbers. To include more than one parameter, you can simply write more than one parameter, separated by a comma. The code below takes in two numbers, represented by x and y, and adds them:
We call the method in a similar manner. If we give the function the following calls:
then the program will print the following to the console:
Using parameters allows us to write code that is flexible and reusable. Writing a method is like telling the program to do something (add two numbers or draw a rectangle on the canvas). Parameters are like giving that method specific instructions ("I want to add 3 and 7" or "I want my greeting message to say their name and my name").
Functions can also take in multiple parameters. If you wanted to print several greetings, you'd likely want them to contain different text depending on the person receiving the greeting. If each of these pieces of information was hard-coded into the method, you would need a separate method for each greeting!
Using parameters allows you to write one printMessage method that can be used to send many greeting messages:
If Karel wants to send a birthday message to Bill Gates and a Halloween card to Steve Wozniak, Karel could write:
This would print two letters to the console:
It's very important to pass arguments to methods in the proper order. Using the printMessage example above, you may know that Karel is the name of the person sending the message and that you want it to start with "Howdy", but the computer does not know this information. The way that the computer finds out which argument goes to which parameter is by the order in which your code passes the arguments into the method. For example, if you wrote:
you would end up with a mixed-up message:
As you can see, order matters when you are using parameters.
