11.15 (Implementing the string class) The string class is provided in the C++ library. Provide your own implementation for the following functions (name the new class MyString): MyString(char ch, int size); MyString(const char chars , int size); MyString append(const MyString& s) ; MyString append (const MyString& s, int index, int n); MyString append(int n, char ch); MyString assign(char* chars) ; MyString assign(const MyString& s, int index, int n); MyString assign(const MyString& s, int n); MyString assign(int n, char ch); MyString substr(int index, int n) const; MyString substr(int index) const; MyString erase(int index, int n)