Introduction about Rustlings

Rustlings is a project that contains small exercises to get you used to reading and writing Rust code. This includes reading and responding to compiler messages!

GitHub Repository: https://github.com/rust-lang/rustlings
The book (for using when learning Rust with Rustlings - include some hint from rustlings): https://doc.rust-lang.org/book/title-page.html
For more details about Rustlings and how to use it, please visit Rustlings GitHub page!

Chapter 0 - Introduction

With the introduction of Rustlings, we learn how to use the Rustlings and how to write the very first Hello World on rust

// The original code:
fn main() {
	println!("Hello {}!");
}

You need to find out the problem and fix it. we can easily see in the code above we have - that is used for print something, and we need to pass a value into it to print out.

//Solution
fn main() {
	println!("Hello {}!", "Rust");
}

You can also pass a variable into it, and more

let name = "Rust";
println!("Hello {}!", name);
//Result; Hello Rust
println!("Hello {1}, {1} is learning {0}", "Rust", "Bob")
// Result; Hello Bob, Bob is learning Rust

Chapter 1 - Variables

Exercise 1

fn main() {
	x = 5;
	println!("x has the value {}", x);
}

Rust uses the let command to define a new variable, so the one is missing here is let command. Easy!

fn main() {
	let x = 5;
	println!("x has the value {}", x);
}

Exercise 2

fn main() {
	let x;
	if x == 10 {
		println!("x is ten!");

	} else {
		println!("x is not ten!");
	}
}

Same as other programming languages, we need to assign an init value to x before we can use the variable.

fn main() {
	let x = 10;
	if x == 10 {
		println!("x is ten!");

	} else {
		println!("x is not ten!");
	}
}

We can also do it in another way

let x;
x = 11

Exercise 3

fn main() {
	let x: i32 = 10;
	println!("Number {}", x);
}

Quite the same as the exercises above, we need to assign a value for the variable 1 thing here is the variable's type is i32, which means we need to assign an integer value for that variable. You can try assigning an float variable to see the error

fn main() {
	let x: i32 = 10.1;
	println!("Number {}", x);
}

// Result: **^^^^** **expected `i32`, found floating-point number**

Exercise 4

fn main() {
	let x = 3;
	println!("Number {}", x);
	x = 5; // don't change this line
	println!("Number {}", x);
}

In Rust we have 2 types of variables: mutable and immutable. For immutable variables, we cannot change the value of the variable. In the example above the error will be "cannot assign twice to immutable variable" We can make the variable mutable to re-assign a new value to it

fn main() {
	let mut x = 3;
	println!("Number {}", x);
	x = 5; // don't change this line
	println!("Number {}", x);
}

You cannot assign a value that has different type than the first value. Example this example below will raise the error: "^ expected floating-point number, found integer"

fn main() {
	let mut x = 3.1;
	println!("Number {}", x);
	x = 5; // don't change this line
	println!("Number {}", x);
}

Exercise 5

fn main() {
	let number = "T-H-R-E-E"; // don't change this line
	println!("Spell a Number : {}", number);
	number = 3; // don't rename this variable
	println!("Number plus two is : {}", number + 2);
}

The same as the exercise 4, we cannot change the type of the variable when we re-assign a new value. What should we do? In Rust we have a thing called Shadowing. It allows us to re-defined the variables (including their types and values).

fn main() {
	let number = "T-H-R-E-E"; // don't change this line
	println!("Spell a Number : {}", number);
	let number = 3; // just add the 'let' word
	println!("Number plus two is : {}", number + 2);
}

Shadowing affects block scope. Example:

fn main() {
	let number = 3;
	let number = number + 1;
	{
		let number = number + 2;
		println!("Number in block is: {}", number);
	}
	println!("Number plus one is: {}", number);
}
// Result:
// Number in block is: 6
// Number plus one is: 4

Exercise 6

const NUMBER = 3;

fn main() {
	println!("Number {}", NUMBER);
}

Constant in Rust sounds like same as the immutable variable, but it has some different

Constant must have a type annotation
We cannot use mut with const
Constants are valid for the entire scope of which they were declared

So for this exercise, we only need to add a type annotation for the const

const NUMBER: i32 = 3;

fn main() {
	println!("Number {}", NUMBER);
}

The first chapter of Rustlings - Variables ends here. TIL:

Working with variables in Rust
Variables initial and value assign
Mutable - Immutable variable, shadowing, constants

Thanks for reading and please add comments below if you have any questions