unresolved external symbol "public: __thiscall [closed]

Answer 1

In your BankAccount class you declare a constructor that takes no arguments

 BankAccount();

but you do not implement it. This is why the linker cannot find it. Provide an implementation for this constructor in your .cpp file and the link step should work.

Answer 2

The "__thiscall" is noise. Read on. The error messages are complaining about BankAccount::BankAccount(void). The header file says that BankAccount has a default constructor, but there's no definition for it.