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:

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/* 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;
        }
}

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