Unit 3, Chapter 1, Lesson 5: Creating Functions

Overview

In this lesson, students learn to define and call procedures (in JavaScript, procedures are called “functions”) in order to create and give a name to a group of commands for easy and repeated use in their code. They will be introduced to functions as a form of abstraction that enables them to write code in larger, more logical chunks and focus on what something does, rather than how it does it. As they explore the use of functions through a sequence of activities in App Lab, they will be asked to think about where they see the need for functions and how these functions can make their code clearer or more concise.

At the end of the lesson students review the concept of abstraction and are introduced to elements of the Create PT in preparation for the Practice PT at the end of the unit.

Purpose

Programming languages must necessarily define the meaning of a set of commands which are generally useful and applicable. In order to extend their functionality, nearly all programming languages provide a means for defining and calling new commands which programmers design to fit the needs of the problems they are trying to solve. Defining functions is an example of how computer scientists use abstraction to solve problems. A programmer will design a solution to a small, well-defined portion of the task and then give a name to the associated code. Whenever that problem arises again, the programmer can invoke the new function by name, without having to solve the problem again. This ability to refer to complex functionality by simple, meaningful names allows for programs to be written in more intuitive ways that reflect the relationships between different blocks of code.

Objectives

Students will be able to:

• Recognize functions in programs as a form of abstraction.
• Write a program that solves a turtle drawing problem using multiple levels of abstraction (i.e. functions that call other functions within your code).
• Explain why and how functions can make code easier to read and maintain.
• Define and call simple functions that solve turtle drawing tasks.

Vocab

• Abstraction – a simplified representation of something more complex. Abstractions allow you to hide details to help you manage complexity, focus on relevant concepts, and reason about problems at a higher level.
• Function – A named group of programming instructions. Functions are reusable abstractions that reduce the complexity of writing and maintaining programs.

New Code

• function myFunction() { // function body, including optional "return" command. }
• Call a function

Getting Started

1. In the previous lesson we created simple turtle drawings using only four commands. At some point you probably wished that more commands were available to you. What was one command you wanted to be able to use and explain why you wanted to use it.
2. Programming languages will always have some commands that are already defined, but there will be many instances when the exact command we want isn’t available. Today we’re going to start exploring a powerful feature of most programming languages that will allow us to overcome this issue and create commands of our own.

Activity–Programming with Functions

1. Log in to code.org
2. Work through the lesson on your own–be sure to READ EVERYTHING!!
3. Evaluate at least 1 program someone else did. Include the name of the person whose code you critiqued. Use the following criteria:
   1. The program draws the diamond
   2. The program defines four functions: right(); drawStep(); drawSide(); and drawDiamond(); The names are less important than the existence of four functions with this functionality.
   3. The program makes a single call to drawDiamond();
   4. The program looks clean and organized

Wrap-up