The point is, that many C# concepts are coming from C++ and C.
In these languages a single character constant (like 'A') is represented as their Ascii value, and despite what one may expect, it's type is not char but int (yes 'A' is an int, the same as writing 65).
Thus, the addition of all these values is like writing a series of ascii character codes, i.e.
var pr= 82 + 71 + 66 + ...;
This has been a design decision in C / C++ at some point (its going back to the 70's with C).
