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:

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
    };