Microsoft Visual C#

Microsoft Visual C# is a reference implementation of C#, included in Visual Studio.

using System;
class Program
{
 static void Main(string[] args)
 {
 Console.WriteLine("Hello, World!");
 }
}

using System;
class Program
{
 static long Factorial(int n)
 {
 if (n == 0)
 return 1;
 else
 return n * Factorial(n - 1);
 }
 static void Main(string[] args)
 {
 for (int i = 0; i < 17; i++)
 Console.WriteLine("{0}! = {1}",i,Factorial(i));
 }
}

using System;
class Program
{
 static long Fibonacci(int n)
 {
 if (n < 3)
 return 1;
 else
 return Fibonacci(n - 1) + Fibonacci(n - 2);
 }
 static void Main(string[] args)
 {
 for (int i = 1; i < 17; i++)
 Console.Write("{0}, ", Fibonacci(i));
 Console.WriteLine("...");
 }
}

using System;
class Program
{
 static void Main(string[] args)
 {
 int A, B, C, D;
 try
 { Console.Write("A = ");
 A = Convert.ToInt32(Console.ReadLine());
 Console.Write("B = ");
 B = Convert.ToInt32(Console.ReadLine());
 Console.Write("C = ");
 C = Convert.ToInt32(Console.ReadLine());
 }
 catch
 { Console.WriteLine("Invalid input");
 return;
 }
 if (A == 0)
 { Console.WriteLine("Not a quadratic equation.");
 return;
 }
 D = B * B - 4 * A * C;
 if (D == 0)
 Console.WriteLine("x = {0}", -B / 2.0 / A);
 else if (D > 0)
 Console.WriteLine("x1 = {0}\nx2 = {1}", (-B + Math.Sqrt(D)) / 2 / A, (-B - Math.Sqrt(D)) / 2 / A);
 else
 Console.WriteLine("x1 = ({0},{1})\nx2 = ({0},-{1})", -B/2.0/A, Math.Sqrt(-D)/2/A);
 }
}