C / C++ / MFC

void CMyEdit::OnChar(UINT nChar, UINT nRepCnt, UINT nFlags) 
{
        TCHAR c = (TCHAR) nChar;

	if(c=='A'||c=='B'||c=='C'||c=='D'||isdigit(c))
        {
         //call base class OnChar() function
         CEdit::OnChar(nChar, nRepCnt, nFlags);
	}
}

const short g_arrAllowed[]={1,2,3,4,5,6,7,8,9,0,'a','b','c','d','e','A','B','C','D','E',VK_BACK,VK_DELETE};
 
void CMyEdit::OnChar(UINT nChar, UINT nRepCnt, UINT nFlags) 
{
        
        for(int i=0;i<sizeof(arrAllowed)/sizeof(short);i++)
        {
          if(nChar==arrAllowed[i])
          {
	 //call base class OnChar() function
         CEdit::OnChar(nChar, nRepCnt, nFlags);
         return;
          }
 }
	
}

"Opinions are neither right nor wrong. I cannot change your opinion. I can, however, change what influences your opinion." - David Crow

void CMyEdit::OnChar(UINT nChar, UINT nRepCnt, UINT nFlags)<br />
{        <br />
     if(nChar=='A'||nChar=='B'||nChar=='C'<br />
      ||nChar=='D'||isdigit(c)||nChar==VK_BACK)<br />
     {         <br />
       //call base class OnChar() function<br />
         CEdit::OnChar(nChar, nRepCnt, nFlags);	}}

CComboBox *c = (CComboBox*) GetDlgItem(IDC_YOUR_COMBOBOX);<br />
c->LimitText(10); // or any value you want.