C# problem with System.Windows.Forms console application

Question

using System;
using System.Windows.Forms;

class RandomInt
{
// main entry point for application
static void Main(string[] args)
{
int value;
string output = "";

    Random randomInteger = new Random();

    // loop times
    for (int i = 1; i <= 20; i++)
    {
        // pick random integer between 1 and 6
        value = randomInteger.Next(1, 7);
        output += value + " "; // append value to output

        // if counter divisible by 5, append newline
        if (i % 5 == 0)
            output += "\n";

    } // end for structure

    MessageBox.Show(output,
                     "Random Numbers from 1 to 6",
                     MessageBoxButtons.OK,
                     MessageBoxIcon.Information);

} // end Main

} // end class RandomInt

Answer 1

Right-Click on project,
[Add]
[Reference...]
System.Windows.Forms

Answer 2

thank you Castorix31, again very much. It is worked