Intermediate Exercism • csharp

Darts

Challenge Overview

Calculate the points scored in a single toss of a Darts game.

Visit the darts exercise on Exercism to read the full instructions and download the exercise files.

Dig Deeper

if statements

`if` statements

using System;

public static class Darts
{
    public static int Score(double x, double y)
    {
        var distanceFromCenter = Math.Sqrt(x * x + y * y);

        if (distanceFromCenter > 10.0)
            return 0;

        if (distanceFromCenter > 5.0)
            return 1;

        if (distanceFromCenter > 1.0)
            return 5;

        return 10;
    }
}

The first step is to calculate the distance from the center of the board, which we can with the cartesian coordinates distance formula

var distanceFromCenter = Math.Sqrt(x * x + y * y);

Before we’ll look at the score calculation, let’s re-iterate the games rules:

Lands	Distance	Points
Outside	> 10 units	0
Outer circle	> 5 units and <= 10 units	1
Middle circle	> 1 unit and <= 5 units	5
Inner circle	<= 1 unit	10

Directly translating this to code gives us:

if (distanceFromCenter > 10.0)
    return 0;

if (distanceFromCenter > 5.0 && distanceFromCenter <= 10.0)
    return 1;

if (distanceFromCenter > 1.0 && distanceFromCenter <= 5.0)
    return 5;

return 10;

However, due to the order of evaluation, we know in our second condition, distanceFromCenter <= 10.0 must always true as otherwise distanceFromCenter > 10.0 would have been true. The same reasoning applies to the distanceFromCenter <= 5.0 condition. We can thus shorten our code to:

if (distanceFromCenter > 10.0)
    return 0;

if (distanceFromCenter > 5.0)
    return 1;

if (distanceFromCenter > 1.0)
    return 5;

return 10;

switch expression

`switch` expression

using System;

public static class Darts
{
    public static int Score(double x, double y)
    {
        return Math.Sqrt(x * x + y * y) switch
        {
            > 10.0 => 0,
            > 5.0 => 1,
            > 1.0 => 5,
            _ => 10
        };
    }
}

The first step is to calculate the distance from the center of the board, which we can with the cartesian coordinates distance formula:

Math.Sqrt(x * x + y * y)

Before we’ll look at the score calculation, let’s re-iterate the games rules:

Lands	Distance	Points
Outside	> 10 units	0
Outer circle	> 5 units and <= 10 units	1
Middle circle	> 1 unit and <= 5 units	5
Inner circle	<= 1 unit	10

Directly translating this to code gives us:

return Math.Sqrt(x * x + y * y) switch
{
    > 10.0 => 0,
    > 5.0 and <= 10 => 1,
    > 1.0 and <= 5.0 => 5,
    _ => 10
};

However, due to the order of evaluation, we know in our second condition, <= 10.0 must always true as otherwise > 10.0 would have been true. The same reasoning applies to the <= 5.0 condition. We can thus shorten our code to:

return Math.Sqrt(x * x + y * y) switch
{
    > 10.0 => 0,
    > 5.0 => 1,
    > 1.0 => 5,
    _ => 10
};

Shortening

When the body of a method is a single expression, the method can be implemented as a member-bodied expression:

public static int Score(double x, double y) =>
    Math.Sqrt(x * x + y * y) switch
    {
        > 10.0 => 0,
        > 5.0 => 1,
        > 1.0 => 5,
        _ => 10
    };

Source: Exercism csharp/darts