Variables and Data Types

In this lesson, we'll explore how Rust handles variables and its basic data types. You'll learn about variable declaration, mutability, and the most common data types you'll use in your Rust programs.

Variables and Mutability

In Rust, variables are immutable by default - a key feature that promotes safer code:

fn main() {
    let x = 5; // Immutable by default
    println!("The value of x is: {}", x);
    
    // This would cause a compile error:
    // x = 6; // Cannot assign twice to immutable variable
    
    // To make a variable mutable, use 'mut':
    let mut y = 5;
    println!("The value of y is: {}", y);
    y = 6; // This works!
    println!("The value of y is now: {}", y);
}

Basic Data Types

Rust is a statically typed language, which means it must know the types of all variables at compile time. The compiler can usually infer the type based on how we use the variable.

Scalar Types

Integers

fn main() {
    let a: i32 = 42;        // 32-bit signed integer
    let b: u32 = 42;        // 32-bit unsigned integer
    let c = 42_i64;         // 64-bit signed integer
    let d = 42_u64;         // 64-bit unsigned integer
    
    println!("Different integer types: {}, {}, {}, {}", a, b, c, d);
}

Floating-Point Numbers

fn main() {
    let x = 2.0;      // f64 (default)
    let y: f32 = 3.0; // f32
    
    println!("Floating point numbers: {}, {}", x, y);
}

Boolean

fn main() {
    let t = true;
    let f: bool = false;
    
    println!("Boolean values: {}, {}", t, f);
}

Character

fn main() {
    let c = 'z';
    let z: char = 'ℤ';
    let heart_eyed_cat = '😻';
    
    println!("Characters: {}, {}, {}", c, z, heart_eyed_cat);
}

Type Conversion

Rust requires explicit type conversion in most cases:

fn main() {
    let x = 42_i32;
    
    // Convert i32 to f64
    let y = x as f64;
    
    // String to number conversion
    let str_num = "42";
    let parsed_num = str_num.parse::<i32>().unwrap();
    
    println!("Original: {}", x);
    println!("Converted to float: {}", y);
    println!("Parsed from string: {}", parsed_num);
    
    // Try changing these values and conversions!
}

Practice Exercises

Try these exercises in the playground above:

Create variables of different numeric types and perform some basic arithmetic
Try converting between different numeric types using the as keyword
Create a string from a number using the to_string() method
Parse a string containing a floating-point number into an f64

Remember: Rust's type system is one of its strongest features, helping catch potential errors at compile time rather than runtime!