extern char *strncat(char *s1, const char *s2, size_t n);
extern char *strcat(char *s1, const char *s2);
extern int strncasecmp(const char *s1, const char *s2, size_t len);
extern char *strncat(char *s1, const char *s2, size_t n);
extern char *strcat(char *s1, const char *s2);
extern int strncasecmp(const char *s1, const char *s2, size_t len);