First write a program to compute factorial based on a number given on
the command line. This program should be simple. For example, to
compute 5!, you would simply type "./factorial 5" on the command line,
assuming that you named your executable factorial. The output of this
program should be "5! is 120."

Secondly, write a program that gets input from the user. For example,
ask the user what factorial they would like to compute. Given this
input (you may read it in as a cstring for simplicity), create a child
process to compute the factorial. Be sure that the parent waits for
the child to finish executing before it exits.

You will need to use fork, execlp and wait system calls for this
assignment.


Read: 111-123
Be sure to think about the practice exercises.
Also answer the following from the book: 3.7, 3.9
Lastly answer: What is swapping and why is it useful?