Some code safety insights

[B1Z0N]

Thanks for your contribution to opensource! There's some code safety improvements possible, for example:

1. scanf return value not taken into account. Possibly here(for example) and in other places.
2. Unfreed memory and unitialized memory access. Possibly here(for example) and in other places. Please check valgrind tool to mitigate this kind of safety flaws.
3. Excessive use of system calls without user input validation. Possibly here(for example) and in other places. Please see how it may be abused here.