Introduction

The functions you’ve used so far can be thought of as black boxes with a big “Go” button on the outside. You hit the button and the function does its work. The work is the same every time. If you want the function to do different work, you have to write a different function.

In this lesson, you’ll learn that functions can be much more powerful. By passing values in to functions, you can make them more flexible so they can be used in a variety of situations. And by calling functions that return values, you can use the results of one function as the input to another. You’ll also learn about ways to make your programs easier to understand and easier to read, even after you’ve added more complexity.

Go Build

Open the "Parameters and Results.playground" file in the folder you downloaded and follow the instructions.

Screenshot of the ParametersAndResults playground

Reflection Questions

You can now build functions that take information in and use it in the work they perform. But the work is still the same. What if you could do different work that depends on the information that’s passed in?

Can you think of some real-life processes and tasks that fit into the various ways you can define a function (with or without parameters, with or without a return type)?

Summary

You can now think of a function as more than a simple black box with a single button. A function is more like a machine in a factory, with arguments going in at one end, work happening inside, and a return value coming out the other end.

With this kind of complexity, functions are capable of doing some powerful work.

When it comes to writing programs that are easy to read and understand, you’ve learned that naming your functions and their arguments is very important. You've also learned that function calls are another type of expression—they can be used anywhere your code expects a value.

If you've been keeping track, you can list all the kinds of expressions you've learned about:

literals
constants and variables
mathematical expressions
function calls

In the next lesson, you’ll learn how your code can make decisions as your program runs. You can use this decision-making ability to write functions that do different work depending on the parameters passed in.