That's plain ASCII.
10 = LF, 13 = CR
That sequence is a common line termination, in this case you're basically reading an empty line.
Numbers 48-57 are numerals 0-9.
The others (40-47, 48) are various signs. Don't know where that would come from.
Anyway you're getting your communication in ASCII, and that you have to wait for a LF/CR termination. And if it's really an ASCII character string, atoi() is back in the picture!