Design and implement a C program to simulate the Unix$/$Linux file system tree. The

program should work as follows.

$($a$).$ Start with a $/$ node, which is also the Current Working Directory $($CWD$).$

$($b$).$ Prompt the user for a command. Valid commands are:

mkdir, rmdir, cd$,$ ls$,$ pwd$,$ creat, rm$,$ save, reload, menu, quit

$($c$).$ Execute the command, with appropriate tracing messages.

$($d$).$ Repeat $(2)$ until the "quit" command, which terminates the program.

The following outlines the suggested organization of the program.

$(1)$ NODE type: Define a C structure for the NODE type containing

$64$ chars: name string of the node;

char: node type: $$D$$ for directory or $$F$$ for file

node pointers: $*$childPtr$,*$siblingPtr$,*$parentPtr;

#include

int main$()$

$\{$

int a$,$ b$,$ c;

a $=4$; b $=5$;

c$=$ Add$($a$,$b$)$;

$//$Add the remaining code

$\}$

$(2)$ Global Variables:

NODE $*$root$,*$cwd; $//$root and CWD pointers

char line$[128]$; $//$user input command line

char command$[16],$ pathname$[64]$; $//$command and pathname strings

char dname$[64],$ bname$[64]$;

$($others as needed$)$

$(3)$ The main function

int main$()$

$\{$

initialize$()$; $//$initialize root noode of the file system tree

while$(1)\{$

get user input line $=[$command pathname$]$;

identify the command;

execute the command;

break if command $=$quit$$;

$(4)$ Get user inputs: Assume that each user input line contains a command with an optional

pathname. The reader may use scanf$()$ to read user inputs from stdin. A better technique is as

follows

fgets$($line$,128,$ stdin$)$; $//$get at most $128$ chars from stdin

line$[$strlen$($line$)-1=0$; $//$kill

at the end of line

sscanf$($line$,\%$s $\%$s$,$ command, pathname$)$;

$(5)$ Identify command:

If$(!$strcmp$($command$,$mkdir$)$

mkdir$($pathname$)$;

else if $(!$strcmp$($command$,$rmdir$)$

rmdir$($pathname$)$;