functions.md

Introduction to Functions

let a : number = 12;
let b : number;

Variables Review

We use the let keyword to declare a new variable, the : symbol to give a type, and the = operator to assign the variable a value.

Uninitialized Variables

To output the value of a variable in Makecode, we use the player.say() command. Let's see what happens when we try to output the two variables a and b.

Exercise: Output the value of the two variables.

player.say(a);
player.say(b);

Function Inputs

So far, all of the code we have written is executed as soon as the green play button is pressed. We can use functions to change aspects of our program using Minecraft's built-in event handlers. But first, we need a function that will assign a value to b.

Just like in Algebra class, we can create a function that takes inputs, and then use that input in the code body of the function.

Example:

``

function setB(num1 : number) {

...

}

``

Exercise: Create a function named setB() that takes one numeric input, num1 and assigns variable b to it.

function setB(num1 : number) {
	b = num1;
}

Calling a User Defined Function

The function definition from the previous step does not actually execute the function; we have to now call the function in order to use it.

Example: setB(12)

Exercise: Call function setB() with a numeric input, and then output the new value of b.

setB(20);
player.say(b)

Variable Scope

All variables in Typescript have a scope, or visibility. So far, all of our code has been executing in the global scope. This means that any variables or functions defined outside of any other function are visible (in scope) anywhere else in the program. That's why the setB() function was able to see and use variable b.

Function setB() included it's own local variable, num1. If we try to use num1 outside of setB() (global scope), the compiler will throw an error.

Exercise: Add a new player.say() statement to output num1 outside the setB() function body.

player.say(num1)

Get and Set Functions

It is common to create functions that will get or set variables. We have already created a function setB() that assigns a value to B. Let's create a new function that will get the value and output it with a player.say() statement.

Since a get function just needs to output a global variable, it does not need any input variable parameters inside it's parenthesis.

Exercise: Define a new function getB() that output the value of b. Then, call getB() to make sure it works.

function getB() {
	player.say(b)
}

getB();

Get and Set part 2

Now that we can get and set variable b, let's define 2 new functions to do the same for variable a.

Exercise: Define functions setA() and getA() and call them.

function setA(num1 : number) {
	a = num1;
}

setA(-5);

function getA() {
	player.say(a);
}

getA();

Event Driven Programming

So far, all of code is non-interactive. Minecraft Makecode does not have standard input commands like most other programming environments. Instead, Minecraft Makecode uses event driven commands to trigger functions based on an event in the game.

When we worked in the block-based environment, we got used to the onChat style commands. Let's create a new player.onChat() command that let's us call our get and set functions. See below for an example of how to create an onChat() statement that uses our functions.

player.onChat("setmyvar", setA);

The onChat() command takes 2 inputs. The first, "setmyvar", is the text the user needs to type in the chat window to trigger the onChat() command. The second input, setA, is the name of the function to call when the correct text is typed. Notice, we only give the name of the function, we do not include the parenthesis or it's input.

With this code, if we were to type "setmyvar" in chat followed by a number, Makecode will see execute the onChat() command and give the number to the setA() function.

Input and Output with onChat()

Now it's time to put everything together. We need to create 4 player.onChat() statements, one for each get and set function for our two variables.

Example: player.onChat("seta", setA);

Exercise: Write the 4 player.onChat() commands that use the 4 functions, setA, getA, setB, and getB that were created above.

player.onChat("seta", setA);
player.onChat("geta", getA);
player.onChat("setb", setB);
player.onChat("getb", getB);

Use Your Functions!

Go into chat and practice using the onChat() commands to change and output the values of variables a and b.