In an attempt to make file input easier for you, we have specified that your first two programs will get their data from standard input using UNIX file redirection. So, when we test your program, we will do this:
vectsort < hw0-data
And your responses should be written to standard output (the screen). This way, you will only need to mess with cin and cout and not have to worry about opening and closing files.
It is VERY important that your program work this way because we will be testing them mechanically.