Create a file named caesar.cpp$.$ In this file, write a program that implements a Caesar cipher.

Your program should expect two command line arguments. The first argument must be either $-$e $($for encryption$)$ or $-$d $($for decryption$).$ The second argument must be a non$-$negative integer. If the user provides the wrong number of command line arguments, if the first argument is not expected, or if the second argument is not composed entirely of the digits $0$ through $9,$ print a usage message and exit with exit code $1$ to indicate that there was an error:

$[$julius@gallia lab$4]$$ $./$caesar

USAGE: caesar $[-$ed$][$key$]$

If the user provides valid command line arguments, your program should read its standard input one line at a time. It should then either encrypt or decrypt the line and print the result. When encrypting, all English letters $($a through z and A through Z$)$ should be "rotated right" by the user$-$supplied key $($an a rotated right $3$ would become a d$,$ and a y rotated right by $3$ would become a b$).$ Capitalization should be preserved, and all non$-$letter characters should be left unchanged.

$[$julius@gallia lab$4]$$ $./$caesar $-$e $3$

abcdefghijklmnopqrstuvwxyz

defghijklmnopqrstuvwxyzabc

Veni, vidi, vici.

Yhql$,$ ylgl$,$ ylfl$.$

When decrypting, all letters should be rotated left.

$[$julius@gallia lab$4]$$ $./$caesar $-$d $5$ Frtw Anshny Trsnf Amor Vincit Omnia

The key may be greater than twenty$-$six. Note that when the key is a multiple of $26,$ the input should be unchanged.