internal command in C program

[naresh6577]

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:

#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