system function: It is used to pass a command to operating system.
int system(const char *str);
abort function: It is used to terminate a program abnormally.
getenv function: It is used to return a pointer to environment data pointed by “a” in environmental table.
char *getenv(const char *a);
mblen function: It is used to obtain length in bytes of a character string.
int mblen(const char *a, size_t b);