Lesson 5

What comes next?

Now that we’ve gone through the 3 major things we work on, we will dive deeper into what we work on the most: the scouting app 📱

What will we do?

Like mentioned before, our app is made with a programming language called Dart.

So, before we go too far into complex code, we will start with the basics of Dart and move our way towards the actual scouting app!

What should I expect for Lesson 5?

We will learn Dart from the start, just like how we learned HTML in Lesson 2.

Introduction to Dart

Learn the basics

Before we go into the actual app, we will start learning Dart from the very beginning.

A good thing is that what we will learn is almost identical in most other programming languages, so learning it well here will give you a head start on other languages as well!

Let’s first go into this website:

https://dartpad.dev/ 

The website is an online IDE (Integrated Development Environment), which simply means a website or app that helps us build and run projects.

First step

When you first go into the website, you will find this code:

void main() {
  for (var i = 0; i < 10; i++) {
    print('hello ${i + 1}');
  }
}

Don’t worry about it for now and just replace it with this code:

void main() {
  // this statement will print hello
  print('hello');
}

Press Run and see what happens on the right half of the screen.

It should show hello on the screen.

Now let’s break down the code one by one.

What is main()?

First, look at the word main(). What does this mean?

This is the main function.

Every time you run any Dart code, the first thing that runs is the main function.

Whatever is inside the curly braces {} is what is inside the function.

What does void mean?

But what does the void mean?

Every function will either return a value or return nothing.

The void indicates that the function will return nothing.

What is a comment?

Now let’s look inside the function. You see the // and a bunch of words following after?

That is called a comment.

Comments do nothing to your code.

Then why do we use comments?

Comments are used to keep your code organized.

Sometimes when your code gets too long, it is hard to find things or know what different parts of the code do.

That is why we write comments. Whenever we come back to the code, we can quickly understand what the code does.

What is print()?

Finally, let’s look at:

print('hello');

As you probably guessed, print() will print whatever is inside the parentheses.

Try replacing hello with any number, like 7.

Now try replacing hello with just hello without the quotation marks.

Did you notice the error?

This is because whenever you want to print a word or a letter, you must use either single quotation marks ('') or double quotation marks ("").

And finally, let’s talk about the semicolon ;.

The semicolon is used at the end of every statement.

Step 2: Variables

Now we will talk about variables.

Variables are things that store a specified value.

Before we dive deeper, look at this code:

void main() {
  int number = 4;
  print(number);
}

Before you put this into the IDE and run it, predict what the result will be.

After running the code, let’s break it down.

Look at the line:

int number = 4;

• int is short for integer.
• An integer is a non-decimal number.
• number is the name of the variable.
• = 4 assigns the value 4 to number.
• The statement ends in a semicolon.

In short, the line declares a variable called number with an integer data type and assigns it the value 4.

At the end, the code prints the variable number, which stores the value 4, so the program prints 4.

Variable data types

Now let’s dive deeper into variables.

Like we discussed before, variables can have different types.

The most popular ones that we will be using are:

• int
• double
• String
• bool

Let’s go one by one to learn what each of them does.

int

int represents whole numbers, including positive numbers, negative numbers, and zero.

Example:

int number = 4;

double

double represents decimal numbers.

Example:

double decimal = 1.6;

String

String represents text and letters.

Example:

String word = "hello";

bool

bool represents either true or false.

Example:

bool example = true;

Try all of these variables in your IDE to truly understand how they work.

You can use the examples given or make your own in the same format.

Matching data types

Now that you know how variables work, it brings up a question:

What happens if you give a variable with a data type a value of a different data type?

Let’s try it.

Replace:

int number = 4;

with:

int number = "four";

You get an error!

This is because the data type of the variable and the value you assign to it must be compatible.

An int cannot store text like "four".

Changing the value of a variable

You can also change the value of a variable.

Try out the code below:

void main() {
  int number = 4;
  print(number);
  number = 7;
  print(number);
}

When you run the program, you can see that it outputs 4 and then 7.

This is because we changed the value of number in the middle of the print statements.

However, you may notice that when we changed the value to 7, we wrote:

number = 7;

and not:

int number = 7;

If you try the second option, you will get an error.

This is because the variable’s data type is declared when the variable is created.

So whenever you want to reuse the same variable, make sure you don’t include the data type again.

For example:

int number = 4;
 
number = 7;
number = 10;

The variable is declared as an int once, and after that, you can change its value as long as the new value is compatible with the variable’s data type.