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.

Example of ambiguous conversion

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

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;
      }
   }
}

Example of void method

A void method invocation in a switch match expression generates CS0151. You can fix the error by calling a method that returns an integral type such as int or long instead.

class C
{
    static void Main()
    {
        switch (M()) // CS0151
        {
            default:
                break;
        }
    }

    static void M()
    {
    }
}