You can construct a string-class string from a C-string directly, as in "string myString ("ABCDEFG");". To construct with a character, however, you must supply a length, as in "string myString (8, '\0');".
I think I've done it.
One more question: Regarding double and int. Actually I don't need double, but I need 64 bit int. Do I have an option to allocate it?