02. Variables.md

Variable Declaration and Type Inference in Rust

In Rust, variable declaration involves specifying a name and optionally a data type. Here's a breakdown of different declaration styles:

• let (Immutable Variables): This is the default way to declare variables in Rust. The compiler infers the data type if not explicitly provided. Once declared, let variables cannot be reassigned.

let x = 10;    // Inferred type: i32
let message = "Hello, world!"; // Inferred type: &str (string slice)

• let mut (Mutable Variables): Use let mut for variables that need to be changed later.

let mut count = 0;
count += 1; // Increment the value of count

• Explicit Type Annotation: While type inference is generally encouraged, you can explicitly specify the type for clarity or to constrain the variable to a specific data type.

let value: i64 = 9223372036854775807; // Explicitly assign i64 type

Numeric Data Types in Rust

Rust provides a variety of integer and floating-point data types to represent different number ranges and precisions. Here's a table summarizing the commonly used types:

Type	Size (bits)	Description
i8	8	Signed integer, range: -128 to 127
i16	16	Signed integer, range: -32,768 to 32,767
i32	32	Signed integer, range: -2,147,483,648 to 2,147,483,647 (default for i if not specified)
i64	64	Signed integer, range: -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
u8	8	Unsigned integer, range: 0 to 255
u16	16	Unsigned integer, range: 0 to 65,535
u32	32	Unsigned integer, range: 0 to 4,294,967,295 (default for u if not specified)
u64	64	Unsigned integer, range: 0 to 18,446,744,073,709,551,615
f32	32	Single-precision floating-point number (approx. 7 decimal digits of precision)
f64	64	Double-precision floating-point number (approx. 15 decimal digits of precision)

Boolean Data Type (bool)

In Rust, the bool data type represents Boolean values: true or false. It's commonly used for conditional statements and decision-making.

let is_raining = true;
let is_sunny = !is_raining; // Logical negation (not)

if is_raining {
  println!("It's raining, bring an umbrella!");
} else {
  println!("Enjoy the sunshine!");
}

String Data Type

Represents a dynamically allocated, mutable string of characters. Use functions like from to create strings.

let greeting = String::from("Hello, world!"); // Allocates memory for the string
greeting.push_str(" Have a nice day!"); // Mutable string modification
println!("{}", greeting); // Prints "Hello, world! Have a nice day!"