Added files

Author: hitesh-bhatnagar

examples/variables.rs examples/01_variables.rsexamples/variables.rs renamed to examples/01_variables.rs

@@ -0,0 +1,171 @@
+use std::io;
+
+// STRUCTS --> defined outside main()
+
+struct User {
+    username: String,
+    email: String,
+    age: u32,
+    is_active: bool,
+}
+
+struct Rectangle {
+    width: f64,
+    length: f64,
+}
+
+// impl = attach methods to a struct
+impl Rectangle {
+    fn new(width: f64, length: f64) -> Self {
+        Self { width, length }
+    }
+
+    // & self = borrow the struct -> don't consume it
+
+    fn area(&self) -> f64 {
+        self.width * self.length
+    }
+
+    fn perimeter(&self) -> f64 {
+        2.0 * (self.width + self.length)
+    }
+
+    fn is_square(&self) -> bool {
+        self.width == self.length
+    }
+}
+
+// ENUMS --> defined outside main()
+enum Direction {
+    North,
+    South,
+    West,
+    East,
+}
+
+// Enum with DATA attached to variants
+enum Shape {
+    Circle(f64),
+    Rectangle(f64, f64),
+    Triangle(f64, f64, f64),
+}
+
+enum Cmd {
+    Echo(String),
+    Cd(String),
+    Exit,
+    Unknown(String),
+}
+
+// FUNCTIONS --> defined outside main()
+
+fn area_of_shape(what_shape: Shape) -> f64 {
+    match what_shape {
+        Shape::Circle(r) => 3.14 * r * r,
+        Shape::Rectangle(w, h) => w * h,
+        Shape::Triangle(a, b, c) => {
+            let s = (a + b + c) / 2.0;
+            (s * (s - a) * (s - b) * (s - c)).sqrt()
+        }
+    }
+}
+
+fn parse_command(input: &str) -> Cmd {
+    let parts: Vec<&str> = input.splitn(2, ' ').collect();
+    match parts[0] {
+        "echo" => Cmd::Echo(parts.get(1).unwrap_or(&"").to_string()), // unwrap_or(&"") means if value exists -> use it, if not -> use empty string
+        "cd" => Cmd::Cd(parts.get(1).unwrap_or(&"").to_string()),
+        "exit" => Cmd::Exit,
+        other => Cmd::Unknown(other.to_string()),
+    }
+}
+
+fn main() {
+    // PART 1 : Creating and Using Structs
+
+    let user = User {
+        // Direct struct initialization
+        username: String::from("alice"),
+        email: String::from("abc@gmail.com"),
+        age: 20,
+        is_active: true,
+    };
+
+    println!("username: {}", user.username);
+    println!("email: {}", user.email);
+    println!("age: {}", user.age);
+    println!("active: {}", user.is_active);
+
+    // PART 2; Structs with Methods
+
+    let rect = Rectangle::new(10.0, 5.0); // constructor like
+    println!("area: {}", rect.area());
+    println!("perimeter {}", rect.perimeter());
+    println!("is square: {}", rect.is_square());
+
+    let square = Rectangle::new(4.0, 4.0);
+    println!("is square: {}", square.is_square());
+
+    // Part 3: Basic Enume with Match
+
+    let dir = Direction::North;
+    match dir {
+        Direction::North => println!("Going north!"),
+        Direction::South => println!("Going south!"),
+        Direction::East => println!("Going east!"),
+        Direction::West => println!("Going west!"),
+    }
+
+    // PART 4 : Enum with Date
+
+    let c = Shape::Circle(5.0);
+    let r = Shape::Rectangle(4.0, 6.0);
+    let t = Shape::Triangle(3.0, 4.0, 5.0);
+
+    println!("Circle area: {:.2}", area_of_shape(c));
+    println!("Rectangle area: {:.2}", area_of_shape(r));
+    println!("Triangle area: {:.2}", area_of_shape(t));
+
+    // PART 6: Option => values that might not exist
+
+    let numbers = vec![1, 2, 3, 4, 5];
+
+    // .get() return Option -- safely gets in index
+    match numbers.get(2) {
+        Some(n) => println!("Found {}", n),
+        None => println!("Not found"),
+    }
+
+    // PART 6: Result - operations that might fail
+
+    let good = "42".parse::<i32>(); // parsing a valid number
+    let bad = "abc".parse::<i32>(); // parsing invalid text
+
+    match good {
+        Ok(n) => println!("Parsed: {}", n),
+        Err(e) => println!("Error: {}", e),
+    }
+
+    match bad {
+        Ok(n) => println!("Parsed: {}", n),
+        Err(e) => println!("could not parse: {}", e),
+    }
+
+    // PART 7: Mini Shell using Enum
+
+    loop {
+        let mut input = String::new();
+        io::stdin().read_line(&mut input).unwrap();
+        let input = input.trim();
+
+        match parse_command(input) {
+            Cmd::Echo(text) => print!("{}\n", text),
+            Cmd::Cd(path) => println!("Would change to : {}", path),
+            Cmd::Exit => {
+                println!("See yaa!!");
+                break;
+            }
+            Cmd::Unknown(c) => println!("Unknown: {}", c),
+        }
+    }
+}