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Compiler Error CS0151

A value of an integral type expected

A variable was used in a situation where an integral data type was required. For more information, see Types (C# Programming Guide).

This error can occur when there is no conversion or if the available implicit conversions result in an ambiguous situation. The following sample generates CS0151.

// CS0151.cs
public class MyClass
{
   public static implicit operator int (MyClass aa)
   {
      return 0;
   }

   public static implicit operator long (MyClass aa)
   {
      return 0;
   }

   public static void Main()
   {
      MyClass a = new MyClass();

      // Compiler cannot choose between int and long
      switch (a)   // CS0151
      // try the following line instead
      // switch ((int)a)
      {
         case 1:
            break;
      }
   }
}

In Visual Studio 2008 and later, a void method invocation generates CS0151. You can fix the error by calling a method that returns an integral type such as int or long.

class C
{
    static void Main()
    {

        switch (M()) // CS0151
        {
            default:
                break;
        }
    }

    static void M()
    {
    }
}
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