Answer:
The buffer has room for 499 characters (you always have to reserve 1 for the terminating \0 character).
The code copies all characters passed in the commandline (argv[1]) into this buffer without checking. If there are more than 499 characters supplied, these will be copied into a memory location that is not intended for it. This will probably cause your program to crash, but if the extra data is somehow executed by the processor as if it were a program, this could be a way to sneak a virus into your computer.
So, while copying data, it is important to always limit the maximum amount to the allocated space.
Talking books could be a means to automatize and generalize such an audio–visual reading experience. ... RWL consists of an experimental reading situation where one reads a text while one can hear it said aloud by a prerecorded speaker or by a text-to-speech system.