Zmienne w Borland C++ [C++ Warning]: W8004 'a' is assigned a value that is never used

Kod źródłowy:

void __fastcall TForm1::Button8Click( TObject * Sender )
{
    long double a = Edit1->Text.ToDouble();
    long double b = Edit2->Text.ToDouble();
    Label4->Caption = a + b;
} 

Logi:
[C++ Error] Unit1.cpp(169): E2015 Ambiguity between '_fastcall System::AnsiString(char)' and '_fastcall System::AnsiString(short)'
[C++ Warning] Unit1.cpp(170): W8004 'b' is assigned a value that is never used
[C++ Warning] Unit1.cpp(170): W8004 'a' is assigned a value that is never used

Chciałem, żeby po kliknięciu na przycisk, liczby w Edit1 i Edit2 dodały się i pokazały w Label4

Label4->Caption = FloatToStr(a + b);