-int strlen(const char *str);
-void *memcpy(void *dest, const void *src, int len);
-void *memset(void *dest, int c, int len);
-int memcmp(const void *av, const void *bv, int len);
-char *strncat(char *dest, const char *src, unsigned int n);
-char *strcat(char *dest, const char *src);
-void strreverse(char s[]);
-void itoa(int n, char s[]);