rust_notes

Using libraries

use std::io;

Includes the io library that is used for taking input and output.

Structure

By default, the main function is the one the is executed first. Default Rust style is to indent with four spaces and not a tab. This is important.

Variables

Declaration of variables occurs as follows:

fn main() {
    let x = 5;
}

This is the declaration of an immutable variable. An immutable variable being changed does not compile. All variables are immutable by default.

To declare a mutable variable (one whose value does not change), we need to use the mut keyword after let.

fn main(){
    let mut x = 5;
    // value of x being changed here.
    x = 6;
}

We can use the let keyword to redefine a variable. This allows us to change a variable’s type, mut does not.

fn main(){
    let x = 5;
    println!({x});
    let x = x + 1;
    println!({x});
}

The previous memory is not being overwritten. Just that x now points to a new memory in the storage with the updated value. This creates two blocks of memories that store values, one with the value 5, another with the value 6.

Constants

Using constants allows you to use hardcoded values in your code. They are always immutable and can be declared globally as well, unlike variables.

Technically variables can be declared globally but only by the use of #[unsafe].

Unlike variables, the type of constant must be explicitly annotated. Like variables, they can be used to perform minor (extremely limited) calculations.

Data Types

Integers - Signed or Unsigned

Bit length	Signed	Unsigned
8	i8	u8
16	i16	u16
32	i32	u32
64	i64	u64
128	i128	u128
architecture-dependent	isize	usize

Signed ints are stored as Two’s Complement.

Integer literals can have _ in them to make them more readable. They can also be annotated with their type at the last, like 786u16. They can also be specified to use number bases such as binary (0b1000), hexadecimal (0xa7), octal (0o77), and a single byte representation (b1).

The single byte representation stores them as u8 behind the scenes.

Add integer overflow for int Types

Floating Points

f32: 32 bit floating point f64: 64 bit floating point

Default is 64 bits. They conform to IEEE-754 Standards

Notes