I have seen lots of people without any program experience have been enrolled into CMU, Berkeley or NYU. You may learn sth as R (time series), Matlab (simulation), C++ may take too much time to get sophisticated. as a fresh graduate, I think Math is more important and also you should find some internship in Big names such as Goldman or Morgan Stanley, these will be a plus. Just a course in C++ on your script will not help, remeber lots of candidates major in computer science and some of them have phd degree, so you'd better strengthen your own advantage.