title: VSCode can't find my basic class in a separate file
body: <p>I am following a tutorial online of C# programming, but the VSCode is not able to find my class definition in a separate file.  I double-checked the class file is under the same namespace.</p>
  <p>Here is my <code>program.cs</code>:</p>
  <pre><code>using System;
  using System.Collections.Generic;
  
  namespace GradeBook
  {
      class Program
      {
          static void Main(string[] args)
          {
              var book = new Book();
               
              var grades = new List&lt;double&gt;() {12.7, 10.3, 6.11, 4.1};
              grades.Add(56.1);
  
              var result = 0.0;
  
              foreach(var number in grades) 
              {
                  result += number;
              }
              result /= grades.Count;
              Console.WriteLine($&quot;Average Result is {result:N1}&quot;);
          }
      }
  }
  </code></pre>
  <p>And I defined a class named <code>Book</code>, which is stored in a file called <code>Book.cs</code>.  Here is the code in <code>Book.cs</code>:</p>
  <pre><code>namespace GradeBook
  {
     class Book 
      {
          
      }
  }
  </code></pre>
  <p>VSCode runs into an issue as follows:</p>
  <blockquote>
  <p>The type or namespace name 'Book' could not be found (are you missing a using directive or an assembly reference?) [GradeBook]</p>
  </blockquote>
  <p>I have checked that the class Book is using the same namespace; both <code>program.cs</code> file and <code>Book.cs</code> file is are in the same folder. How can I fix this issue?</p>