void clrscr(void) 
    { // clear screen function  
    COORD                       coordScreen = { 0, 0 };
    DWORD                       cCharsWritten;
    CONSOLE_SCREEN_BUFFER_INFO  csbi;
    DWORD                                       dwConSize;
    HANDLE                      hConsole = GetStdHandle(STD_OUTPUT_HANDLE);
    GetConsoleScreenBufferInfo(hConsole, &csbi);
    dwConSize = csbi.dwSize.X * csbi.dwSize.Y;
    FillConsoleOutputCharacter(hConsole, TEXT(' '), 
                               dwConSize, coordScreen, &cCharsWritten);
    GetConsoleScreenBufferInfo(hConsole, &csbi);
    FillConsoleOutputAttribute(hConsole, csbi.wAttributes, 
                               dwConSize, coordScreen, &cCharsWritten);
    SetConsoleCursorPosition(hConsole, coordScreen);
    }