How Do I use the WM_CHAR , WM_KEYDOWN , WM_KEYUP

HOW DO I IMPLEMENT THE WM_CHAR ,WM_KEYDOWN, WM_KEYUP MESSAGES IN MY DIALOG BOX Application

 I tried this out but it did not work why???


Void CASCIIDlg::OnKeyDown(UINT nChar, UINT nRepCnt, UINT nFlags)
{
// TODO: Add your message handler code here and/or call default

         MessageBox("hai");
         
     CDialog::OnKeyDown(nChar, nRepCnt, nFlags);
}


The message hai was not printed,when i pressed a key.


 if i want to detect a keypress what should i do

 i tried this but it did not work


void CASCIIDlg::OnKeyDown(UINT nChar, UINT nRepCnt, UINT nFlags)
{
      if(nChar == VK_A)
       MessageBox("hai");
         
     CDialog::OnKeyDown(nChar, nRepCnt, nFlags);
}

    by using the code above i am trying to print the  
    message "hai" when the A key is pressed down but it
    not respond me.

    explain me how do i make use of VIRTUAL KEYS.


    give me a small example coding which clearly explaines
    how to implement these windowsmessages.

   I am working in dialog based application.