TFormWithEdit* FormWithEdit = 0;
try
{
    FormWithEdit = new TFormWithEdit(this);
    if ( FormWithEdit->ShowModal() == mrOK )
    {
        m_MyVar = FormWithEdit->m_PublicVar
    }
}
__finally
{
    delete FormWithEdit;
}

                                              
#include <Dialogs.hpp>
void __fastcall TForm1::Button1Click(TObject *Sender)
{
  AnsiString InputString = InputBox("Input Box", "Prompt", "Default string");
}