C#

using System.Windows;

namespace Hello {

  public partial class MainWindow : Window {
    public MainWindow() {
      InitializeComponent();
    }

    public void Terminate(object sender, RoutedEventArgs evtArg) {
      Application.Current.Shutdown();
    }
  }
}

public void Terminate(object sender, RoutedEventArgs evtArg) {
  Application.Current.Shutdown();
}

<Window x:Class="Hello.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        mc:Ignorable="d"
        Title="Hello" Height="100" Width="120">
  <StackPanel HorizontalAlignment="Left">
    <TextBlock x:Name="textBlock" Text="Hello World"/>
    <Button x:Name="button" Content="OK" Click="Terminate"/>
  </StackPanel>
</Window>

<StackPanel HorizontalAlignment="Left">
  <TextBlock x:Name="textBlock" Text="Hello World"/>
  <Button x:Name="button" Content="OK" Click="Terminate"/>
</StackPanel>

#include <iostream>

int main() {
    std::cout << "Hello World!";
    return 0;
}

Quote:

Is Windows Forms a requirement? A major part of C# GUI programming today is done with WPF, Windows Presentation Foundation.

private static int FactorialRecursive(int x)
    {
    return (x > 1 ? x * FactorialRecursive(x - 1) : 1);
    }
private static int FactorialIterative(int x)
    {
    int f = 1;
    while (x > 1)
        {
        f *= x--;
        }
    return f;
    }

private int CalculateProbabilityOfDrawNumbersFromAllNumbers(int drawNumbers, int allNumbers)
{
    return ((Factorial(allNumbers) * Factorial(80 - allNumbers)) / (((Factorial(80) * ((Factorial(drawNumbers) * Factorial(allNumbers - drawNumbers)) * (Factorial(20 - drawNumbers) * Factorial(((80 - allNumbers) - (20 - drawNumbers)))))) / (Factorial(20) * Factorial(80 - 20)))));
}

private static int Factorial(int x)
{
    int f = 1;
    while (x > 1)
    {
        f *= x--;
    }
    return f;
}