depth-first traversal of directories

Some code I whipped up in about an hour to do a depth-first traversal of given directory. Was wondering if anyone can critique this code and maybe suggest some things to do differently, etc. Am I correct in assuming that depth-first traversal has possible bugs due to running out of memory, etc ? Also, this program is just a template for the do_dir() function itself that would traverse directories, and does nothing useful at the moment save print the directories that it currently opens. In the future I could use it for any number of utilities that would have a directory traversal need.

Thanks

Code:

/* show.c */
#include <stdio.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <dirent.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <stdlib.h>

#define VALIDDIR 1
#define SUBTRACT 0
#define ADD 1

char fullpath[PATH_MAX];
char *curpath = &fullpath[0]; 

int do_stat(const char *dname);
void do_dir(const char *dirname);
void update_fpath(const char *dname, int method);

int main(int argc, char *argv[])
{
	if (argc != 2) {
		fprintf(stderr, "Usage: show directory\n");
		exit(1);
	}

	do_dir(argv[1]);
	return 0;
}

void do_dir(const char *dirname)
{
	DIR *p;
	struct dirent *t;
	char lastdir[PATH_MAX];

	getcwd(lastdir, PATH_MAX);
	update_fpath(dirname, ADD);

	if ((p = opendir(dirname)) == NULL) {
	       fprintf(stderr, "Couldn't open %s: %s\n",
		       fullpath, strerror(errno));
	} else {
		printf("opening %s\n", fullpath);
		chdir(dirname);
 		while (t = readdir(p)) 
			if ((do_stat(t->d_name)) == VALIDDIR)
				do_dir(t->d_name);
		chdir(lastdir);
		closedir(p);
	}
	update_fpath(dirname, SUBTRACT);

}

int do_stat(const char *dname)
{
	struct stat t;

	lstat(dname, &t);

	switch(t.st_mode & S_IFMT) {
	case S_IFDIR:
		if (strcmp(dname, ".")  != 0 &&
		    strcmp(dname, "..") != 0)
			return VALIDDIR;
		break;
	default:
		break;
	}

	return 0;
}
			
void update_fpath(const char *dname, int method)
{
	switch (method) {
	case ADD:
		strcpy(curpath, dname);
		curpath += strlen(dname);
		strcpy(curpath, "/");
		curpath += strlen("/");
	break;
	case SUBTRACT:
		curpath -= (strlen(dname) + 1);
		*curpath = '\0';
	break;
	default:
	break;
	}
}