Shape Area Calculator

Part of the Object Oriented Programming section of Coddy's Rust journey — lesson 61 of 61.

Challenge

Easy

This final challenge brings together traits, trait objects, and polymorphism to solve a practical problem: calculating the total area of different shapes stored in a single collection.

Let's build a shape area calculator that demonstrates the power of trait objects and polymorphism! You'll create a system where different shapes—circles and squares—can be stored together in a single collection and have their total area calculated through a unified interface.

You'll organize your code across three files:

shape.rs: Define the Shape trait with an area method that returns an f64. This trait establishes the contract that all shapes must fulfill.
shapes.rs: Create two structs that implement your trait. A Circle has a radius (f64), and a Square has a side (f64). Each struct should implement the Shape trait with its appropriate area formula. For circles, use 3.14159 as π.
main.rs: Bring in both modules and create a total_area function that accepts a Vec<Box<dyn Shape>> and returns the sum of all areas. Using the provided inputs, create a circle and a square, store them in a vector of trait objects, calculate the total area, and print the result.

The area formulas are:

Circle: 3.14159 × radius × radius
Square: side × side

Your output should display the total area of all shapes:

Total area: {total}

For example, with inputs 2.0 (circle radius) and 3.0 (square side):

Total area: 21.56636

This is because: Circle area = 3.14159 × 2² = 12.56636, Square area = 3² = 9, Total = 21.56636

And with inputs 1.0 and 4.0:

Total area: 19.14159

You will receive two inputs: the circle's radius and the square's side length (parse both as f64).

Try it yourself

mod shape;
mod shapes;

use shape::Shape;
use shapes::{Circle, Square};

// TODO: Implement the total_area function
// It should accept a Vec<Box<dyn Shape>> and return the sum of all areas as f64
fn total_area(shapes: Vec<Box<dyn Shape>>) -> f64 {
    // TODO: Calculate and return the sum of all shape areas
    0.0
}

fn main() {
    let mut input1 = String::new();
    std::io::stdin().read_line(&mut input1).expect("Failed to read line");
    let radius: f64 = input1.trim().parse().expect("Invalid number");

    let mut input2 = String::new();
    std::io::stdin().read_line(&mut input2).expect("Failed to read line");
    let side: f64 = input2.trim().parse().expect("Invalid number");

    // TODO: Create a Circle with the given radius
    // TODO: Create a Square with the given side
    // TODO: Store both shapes in a Vec<Box<dyn Shape>>
    // TODO: Call total_area and print the result in the format: "Total area: {total}"
}