C# Error CS0563 – One of the parameters of a binary operator must be the containing type

C# Error

CS0563 – One of the parameters of a binary operator must be the containing type

Reason for the Error & Solution

One of the parameters of a binary operator must be the containing type

The method declaration for an must follow certain guidelines.

Example

The following sample generates CS0563:

// CS0563.cs  
public class iii  
{  
    public static implicit operator int(iii x)  
    {  
        return 0;  
    }  
    public static implicit operator iii(int x)  
    {  
        return null;  
    }  
    public static int operator +(int aa, int bb)   // CS0563
    // Use the following line instead:  
    // public static int operator +(int aa, iii bb)
    {  
        return 0;  
    }  
    public static void Main()  
    {  
    }  
}