Question

How to calculate the area, diameter, and circumference of a circle in Rust

Answer 1

use std::f64::consts::PI;

fn main() {
    let radius = 3.0;
    
    let area = PI * radius * radius;
    println!("Area = {:.2}", area);
    
    let diameter = 2.0 * radius;
    println!("Diameter = {:.2}", diameter);
    
    let circumference = 2.0 * PI * radius;
    println!("Circumference = {:.2}", circumference);
}


  
/*
run:

Area = 28.27
Diameter = 6.00
Circumference = 18.85
  
*/

 

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Answer 2

use std::f64::consts::PI;
use std::fmt;

/// Custom error type for circle calculation failures.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum CircleError {
    NegativeRadius,
}

impl fmt::Display for CircleError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            CircleError::NegativeRadius => write!(f, "Radius cannot be negative or NaN."),
        }
    }
}

// Implement standard Error trait for interoperability
impl std::error::Error for CircleError {}

/// Structure to hold the calculated geometric metrics of a circle cleanly.
#[derive(Debug, Clone, Copy)]
pub struct CircleMetrics {
    pub diameter: f64,
    pub circumference: f64,
    pub area: f64,
}

/// Calculates the diameter, circumference, and area of a circle.
/// 
/// # Arguments
/// * `radius` - The radius of the circle (must be a non-negative number).
/// 
/// # Returns
/// * `Result<CircleMetrics, CircleError>` - The calculated metrics on success, or an error if invalid.
pub fn calculate_circle_metrics(radius: f64) -> Result<CircleMetrics, CircleError> {
    // Guard clause: radius cannot be negative or NaN
    if radius < 0.0 || radius.is_nan() {
        return Err(CircleError::NegativeRadius);
    }

    let diameter = 2.0 * radius;
    let circumference = 2.0 * PI * radius;
    
    // Standard multiplication (radius * radius) is more efficient than powi() or powf()
    let area = PI * (radius * radius);

    Ok(CircleMetrics {
        diameter,
        circumference,
        area,
    })
}

fn main() {
    let radius = 3.0;

    // Handle the Result using pattern matching
    match calculate_circle_metrics(radius) {
        Ok(metrics) => {
            println!("Radius: {:.2}", radius);
            println!("Diameter: {:.2}", metrics.diameter);
            println!("Circumference: {:.2}", metrics.circumference);
            println!("Area: {:.2}", metrics.area);
        }
        Err(e) => {
            eprintln!("Error: {}", e);
            std::process::exit(1);
        }
    }
}


/*
run:

Radius: 3.00
Diameter: 6.00
Circumference: 18.85
Area: 28.27

*/

 

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