Quiz

I'm having a  problem with a quiz question.  I have posted it below.  There are no Xs in the question, but they display when viewed as you can see below. Where are these "X's" coming from?  Can someone please help me with this?

Given the function strange, select the values of one and letter after these statements execute:
 int Xone= 5;
 char letter = A;
 strange(one, letter);

void strange(int & u, char & ch)

{
   int a;
   u = 2 * u;
   a = static_cast<int>(ch);
   a++;
   ch = static_cast<char>(a);
}