Can not call a function from a C# DLL

I created a DLL in C#, and try to call a function from it. But it has an error:

> Unhandled Exception: System.IO.FileNotFoundException: Could not load file or assembly 'System.Runtime, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The system cannot find the file specified.

My DLL code:

using System;
namespace Draf_Lib
{
    public class Class1
    {
        public static int add(int x, int y) { return x + y; }
    }
}

And here is my C# code to call the function from it:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
//using MacroLib;
using Draf_Lib;

namespace Draft1
{
    internal class Program
    {
        static void Main(string[] args)
        {
            System.Console.WriteLine("Hello");
            Class1 c = new Class1();
            int b = Class1.add(9, 8);
            Console.WriteLine(b);
        }
    }
}

I already included the library as a reference. Can anyone suggest me a way to fix it?

This is because you chose the wrong target framework when creating the project. Here's an example where I reproduce your problem:

1. First, I selected Class Library when creating the class library, and the target framework was selected as .net 6.0

2. Then I created a Console App (.net framework) and selected the target framework as .net framework 4.7.2

3. The following error was reported when I introduced the dll and ran the project.

In fact, you should choose Console App when creating a console program, as follows. The target framework can choose .net 6.0.