//Precondition: hMy_string is the handle to a valid My_string object. //Postcondition: Returns the address of the first element of the string object
// for use as a c-string. The resulting c-string is guaranteed to be NULL
// terminated and the memory is still maintained by the string object though
// the NULL is not actually counted as part of the string (in size).

Required:
Finish this function by using the C language.