internal command in C program

Hii
I need to implement internal command :clear,dir <directory> ,environ and quit in C program using Unix..
i wrote program but i m not sure with output whether it is right or wrong
here is my code:

Code:

---


#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
int main(int argc, char *argv[])
{
        int i,n;
        char *s;
        //extern char **environ;
        extern char **environ;
        if(argc==2)
        {
               
                printf("Myshell??");
                scanf("%s",s);
                if(strcmp(s,"clear")==0)
                {
                        system("clear");
                       
                }
                else if(strcmp(s,"quit")==0)
                {
                        exit(0);
                }
                else if(strcmp(s,"environ")==0)
                {
                                       
                        while(*environ)
                        printf("%s\n",*environ++);

                }
               
        }
        return 0;
}

---

when i run my program i need to enter

a.out r
Myshell??clear
and gives output to clear sceen
but how to implement quit command(exit)and dir <directory>command??

Help me..

Thanks
Rupal