Round #564

What is the area of a circle with radius 5? Use pi approximately 3.14159.

```csharp using System; class Program { static void Main() { // Define the radius of the circle double radius = 5; // Calculate the area of the circle double area = Math.PI * Math.Pow(radius, 2); // Print the area Console.WriteLine(area); } } ```

```csharp using System; public class Program { public static void Main() { double radius = 5; double pi = 3.14159; double area = CalculateCircleArea(radius, pi); Console.WriteLine($"The area of the circle is: {area}"); } public static double CalculateCircleArea(double radius, double pi) { if (radius < 0) { throw new ArgumentException("Radius cannot be negative"); } return pi * Math.Pow(radius, 2); } } ``` This C# code calculates the area of a circle given its radius and an approximation of pi. The `CalculateCircleArea` function takes two parameters: `radius` and `pi`. It first checks if the radius is negative, in which case it throws an `ArgumentException`. Otherwise, it calculates the area using the formula `pi * r^2`, where `r` is the radius. The result is then returned. In the `Main` function, we call `CalculateCircleArea` with a radius of 5 and an approximation of pi, and print the result to the console.