C / C++ / MFC

/////////////////////////////////////////////////////////////////////////////
// CMyTextBox window

class CMyTextBox : public CEdit
{
// Construction
public:
	CMyTextBox();

// Attributes
public:

// Operations
public:

	bool InFlag; // After Press Enter InFlag = true;
	CString RetVal; // store return value

// Overrides
	// ClassWizard generated virtual function overrides
	//{{AFX_VIRTUAL(CMyTextBox)
	//}}AFX_VIRTUAL

// Implementation
public:
	CString GetString();
	double GetNumber();
	virtual ~CMyTextBox();

	// Generated message map functions
protected:
	//{{AFX_MSG(CMyTextBox)
	afx_msg void OnKeyDown(UINT nChar, UINT nRepCnt, UINT nFlags);
	//}}AFX_MSG

	DECLARE_MESSAGE_MAP()
};


// CPP file======================================================

// CMyTextBox message handlers

void CMyTextBox::OnKeyDown(UINT nChar, UINT nRepCnt, UINT nFlags)
{
    // TODO: Add your message handler code here and/or call default
    if (nFlags == 28) // Enter press
        GetWindowText(RetVal);
    CEdit::OnKeyDown(nChar, nRepCnt, nFlags);
}

double CMyTextBox::GetNumber()
{
// how to get return here after press enter by user
    if (InFlag == true)
        return atof(RetVal);
    return 0;
}

CString CMyTextBox::GetString()
{
// how to get return here after press enter by user
    if (InFlag == true)
        return RetVal;
    return "";
}