As previously noted the // is used indicate a
comment in
C++.
Interestingly, a common assertion about the C programming language is that the compiler ignores all whitespace in your code, so that if you really wanted to, you could type an entire programme onto a single line (see: obfuscated C). This is not entirely true because the "newstyle" comment found in C++ (i.e. //) uses the end of line (EOL) to terminate your statement. Now isn't that interesting?
Hopefully you'll be able to use this information to your advantage to grift some 133t h4X0r out of some hard earned cash.