Rust Study Day1

• Rust Study Day1
  • 1. Hello, world!
    • 1.2. Run Hello, world!
  • 2. Variables, functions and process controls
    • 2.1. Variables
    • 2.2. Functions
    • 2.3. Process controls
  • Day Day Conclusion

1. Hello, world!

Whatever you do, you must start with a hello world.

Recommand use cargo new to create a new project.
So, let’s create a new project.

Type the following command in your vscode terminal:

cargo new hello_world_rust
cd hello_world_rust
code .

Now, you can see the project in your vscode navigator located on the left.

1.2. Run Hello, world!

Open the src/main.rs file.

// main.rs 
fn main() {
    println!("Hello, world!");
}

Let’s run the project.
Type the following command in your vscode terminal:

cargo run

You will see the “hello world!” in your terminal.

2. Variables, functions and process controls

2.1. Variables

• Variables are used to store data.
• Variables are declared using the let keyword.
• Variables are immutable.
• If you want to change the value of a variable, you must re-declare it or use the mut keyword.
• And rust can auto infer the type of the variable. Like C# [var].

Some examples:

let a = 1;
let b = 2;
a =3; // Ops, error! a is immutable!

let mut c = 3;
c = 4; // Ok, c is mutable!

2.2. Functions

• Functions are used to perform a specific task.
• functions are declared using the fn keyword.
• Different functions can have a different prefix type. Such as: pub, pub(crate),etc …

pub mod funtions; looks seem as use crate::math_functions;

Some examples:

    // math_functions.rs 
    fn add(a: i32, b: i32) -> i32 {
        a + b
        return a + b;
    }

    pub fn substract(a: i32, b: i32) -> i32 {
        a - b
        return a - b;
    }

    // main.rs 
    use crate::math_functions;

    fn main() {
        let a = 1;
        let b = 2;
        println!("add: {}", add(a, b)); // Ops! Fault! Due to the add function is private in the math_functions.rs file.

        println!("substract: {}", math_functions::substract(a, b)); // Ok! substract is public in the math_functions.rs file. And the crate keyword is used to import the math_functions.rs file.

more info for Rust Functions and Rust Module

CHINESE: Rust 程序设计语言 中文版

2.3. Process controls

• Rust has a powerful control flow mechanism.
• Rust has 3 control flow mechanisms: if, for, while,loop,match…

// if
if number < 5 {
        println!("condition was true");
    } else if number > 8 {
        println!("condition was false");
    } else {
        println!("condition was neither true nor false");
}

// match
let match_num = 10;
match match_num {
    1 => println!("match_num is 1"),
    2 => println!("match_num is 2"),
    10 => println!("match_num is 10"),
    _ => println!("match_num is not 10"),
}

// for
// from 1 to 9, left close, right open
// but for i in 1..=10, it from 1 to 10. left close, right close
for number in 1..10 {
    println!("the number is: {}", number);
    if number % 2 == 0 {
        println!("the number is even");
        break;
    }
}


// iterator
for ele in [1, 2, 3, 4, 5] {
    println!("the element is: {}", ele);
}

// while
let mut while_num = 1;
while while_num < 10 {
    println!("the number is: {}", while_num);
    while_num += 1;
    if while_num % 2 == 0 {
        println!("the number is even");
        break;
    }
}

// loop
let mut loop_num = 1;
loop {
    println!("the number is: {}", loop_num);
    loop_num += 1;
    if loop_num % 2 == 0 {
        println!("the number is even");
        break;
        }
}

What’s the difference between if and match?

• if is a conditional statement, and match is a pattern matching statement.

Day Day Conclusion

• Need to learn more about rust. Such as:
  • use crate::[m];
  • pub mod [m];
• Rust is a mutable and imutable language.