Where can be an error?

Question

C++ / C#

using System;

using System.Windows.Forms;

namespace App1
{
    class App
    {
        static void Main()
        {
            Console.WriteLine("Testing");

            MessageBox.Show("Hello, developer!");

            Console.ReadKey();
        }
    }
}

Compiling this code in visual studio 2017 - an error occurs, they say, a build error
Compiling the same code like this: "C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\MSBuild\15.0\Bin\Roslyn\csc. exe" Program.cs - compiles and runs without any problems
I also noticed that when I entered in visual studio 2017 using System.Windows.Forms the word forms did not appear in the menu. Could this have something to do with it not compiling?

Answer 1

Maybe because you have a console project, and the System.Windows.Forms library is not in it?

Answer 2

By the way, this is not the first time