UILabel.text = @"sin(??)"; gives output: sin(] UILabel.text = @"??/H"; gives compiler warning about unknown escape string What is going on? I could probably get around this by doing something like.. NSString *unknownString = @"??"; // I know @"??" displays fine UILabel.text = [NSString stringWithFormat: @"sin(%@)", unknownString]; BUT I don't want to, I have to work with a lot of ??s in strings, and I need them to not frack up all the time. I've have tried searching extensively and looking at articals on escaping strings, but cannot figure out the real reason behind this mystery. Probably because Google appears to ignore the ?? in "?? NSString" or "?? escape character"