Button click event is not working

See more:

C++

Windows

I got a vc++ application to perform soft keyboard. If I have 2 button in my dialog. One for sending keystroke of a and another will act as shift key for generating A. My code is as follows

void CKeyBoardDlg::OnBnClickedButton33()  //for a
{
    keybd_event(0x41,0,0,0);
    keybd_event(0x41,0,KEYEVENTF_KEYUP,0);
}

void CKeyBoardDlg::OnBnClickedButton45()  //for shift
{
    if(m_nFirst==1)
    {
        m_nFirst=0;
        keybd_event(0x10,0,0x002,0);
    }
    else if(m_nFirst==0)
    {
        keybd_event(0x10,0,0,0);
        m_nFirst=1;
    }
}

My question is that once I click on the button45 shiftkey is in pressed state based on logic. So I can create A by pressing button33 next. But my problem is that when I click again on button45 the event is not working and hence it affects every keyboard shortcuts and activities. What is the problem??? Why is it not invoked?

Is there any another way to send capital letter by keystroke event(keybd_event).