c++ coding

I need to do the following

1.) overload input operator>> a bigint in the following manner: Read in any number of digits [0-9] until a semi colon ";" is encountered. The number may span over multiple lines. You can assume the input is valid.

2.) overload the operator+ so that it adds two bigint together. bigint operator+(const bigint&) const;

3.) overload the subscript operator[]. It returns the digit where i is the 10ⁱposition. So the first digit is the the one's place (10⁰) and the second digit is 10¹(ten's place).

may you help me on how can i define them in header file then overload in cpp please.