operations between value type and reference type

      string s = "Hello" + 5;

      Console.WriteLine(s); // Hello5

However, what's actually happening here is that string concatenation operator is defined between either 2 strings or between a string and an object. In the latter case, the ToString() method is applied to the object and then that is concatenated with the string.

So, in the example, the following is (in effect) taking place:
    
     object obj = 5;
     string s = "Hello" + obj.ToString();
     Console.WriteLine(s); // Hello5