When one button is selected, the other round buttons of the (same) group are empty . The user can select another by clicking a new choice, which empties the previous selection. Here is an example from the Microsoft Windows 95 Shut Down dialog box:

This technique of selecting is referred to as mutually-exclusive.

To indicate what a radio butto is used for, it may be accompanied by static text. That text is simply a string and it can be positioned to the left, above, to the right, or under the round box.

1. Start Microsoft Visual Studio
2. To start a new project, on the main menu, click File -> New Project...
3. In the middle list, click MFC Application and set the name to Operations
4. Click OK
5. In the first page of the MFC Application Wizard, click Next
6. In the second page of the wizard, click Dialog Based and click Next
7. In the third page of the wizard, click Finish
   

Radio buttons usually come in a group. Based on this, before creating radio buttons, you should first add a group box (or any appropriate container) to a dialog box (or to the object that will host the radio buttons; an example would be a Picture frame).

To visually create a radio button, on the Toolbox, click the Radio Button object and click the desired area on the host window. In the same way, add one or more radio buttons.

As a Windows control, the radio button is based on the CButton class which, like all other constrols, is based on CWnd. As far as the Win32 and the MFC libraries are concerned, a radio button is first of all, a button. Therefore, to programmatically create a radio button, declare a variable or a pointer to CButton using its default constructor. Like all other MFC controls, the CButton class provides a Create() member function to initialize it. The syntax of this member function for a button is:

BOOL Create(LPCTSTR lpszCaption,
	    DWORD dwStyle,
	    const RECT& rect,
	    CWnd* pParentWnd,
	    UINT nID);

The lpszCaption argument is the string of the label that accomponies the radio button. The differences of radio buttons are set using the dwStyle argument. A radio button must have the BS_RADIOBUTTON value.

When setting the rect argument, provide enough space for the control because, by default, it will be confined to that rectangle and cannot display beyond that. Here are two examples:

BOOL CExerciseDlg::OnInitDialog()
{
    CDialog::OnInitDialog();

    // Set the icon for this dialog. The framework does this automatically
    // when the application's main window is not a dialog
    SetIcon(m_hIcon, TRUE); // Set big icon
    SetIcon(m_hIcon, FALSE); // Set small icon
    
    // TODO: Add extra initialization here
    CButton *rdoSmall = new CButton;
    CButton *rdoMedium = new CButton;
    
    rdoSmall->Create(Something,
		WS_CHILD | WS_VISIBLE | BS_RADIOBUTTON,
		CRect(130, 40, 200, 50), this, 0x12);

    rdoMedium->Create(Something,
		WS_CHILD | WS_VISIBLE | BS_RADIOBUTTON,
		CRect(130, 70, 200, 80), this, 0x14);

    return TRUE; // return TRUE unless you set the focus to a control
}

1. Design the dialog box as follows:
    

   Control  Caption ID  Align Text Group Box Calculation      Static Text Number &1:      Edit Control    IDC_OPERAND1 Right  Static Text Number &2:      Edit Control   IDC_OPERAND2 Right  Picture          Static Control Result:      Edit Control   IDC_RESULT  Right Group Box Select an Operation      Radio Button       Radio Button       Radio Button       Radio Button

2. Right-click each of the edit controls and click Add Variable... Then create the variables as follows:
    

   ID
   	Category	Type	Name
   IDC_OPERAND1	Value	double	m_Operand1
   IDC_OPERAND2	Value	double	m_Operand2
   IDC_RESULT	Value	double	m_Result

Primary Characteristics of Radio Buttons

   .

The Caption of a Radio Button

The text a radio button displays is referred to as its caption. That text should be explicit enough for the user to figure out the role of an item in the group. To visually specify the caption of a radio button, after adding the control, replace the value of the Caption field in the Properties window. If you are programmatically creating the control, pass its caption as the first argument. Here are examples:

BOOL CExerciseDlg::OnInitDialog()
{
    CDialog::OnInitDialog();

    // Set the icon for this dialog. The framework does this automatically
    // when the application's main window is not a dialog
    SetIcon(m_hIcon, TRUE); // Set big icon
    SetIcon(m_hIcon, FALSE); // Set small icon
    
    // TODO: Add extra initialization here
    CButton *rdoSmall = new CButton;
    CButton *rdoMedium = new CButton;
    
    rdoSmall->Create(_T("Small"),
		WS_CHILD | WS_VISIBLE | BS_RADIOBUTTON,
		CRect(130, 40, 200, 50), this, 0x12);

    rdoMedium->Create(_T("Medium"),
		WS_CHILD | WS_VISIBLE | BS_RADIOBUTTON,
		CRect(130, 70, 200, 80), this, 0x14);

    return TRUE; // return TRUE unless you set the focus to a control
}

If the control exists already, to programmaticalyl change its caption, call the CWnd::SetWindowText() member function.

1. On the dialog box, click the first radio button
2. In the Properties window, click Caption and type &Addition
3. Change the captions of the other radio buttons as follows:
4. Design the dialog box as follows:
    

   Control  Caption ID  Group Box Select an Operation    Radio Button &Addition IDC_ADDITION Radio Button &Subtraction IDC_SUBTRACTION Radio Button &Multiplication IDC_MULTIPLICATION Radio Button &Division IDC_DIVISION

As described already, to select a radio button, the user can click it. To indicate to the user that a button has been selected, it should display a dot in its round box. To visually allow the user to automatically display its dot, in the Properties window, set the Auto property to True. To programmatically allow the user to select a radio button, when creating it, add the BS_AUTORADIOBUTTON style. Here are examples:

int CExerciseDlg::OnCreate(LPCREATESTRUCT lpCreateStruct)
{
    if (CDialogEx::OnCreate(lpCreateStruct) == -1)
	return -1;

    // TODO:  Add your specialized creation code here
    CWnd *ctlGroupBox = new CWnd;
    CButton *rdoSmall = new CButton;
    CButton *rdoMedium = new CButton;
    CButton *rdoLarge = new CButton;

    ctlGroupBox->Create(_T("BUTTON"),
			_T("Pizza Size"),
			WS_CHILD | WS_VISIBLE | BS_GROUPBOX,
			CRect(10, 10, 200, 160),
			this,
			IDC_PIZZASIZE);

    rdoSmall->Create(_T("Small"),
		     WS_CHILD | WS_VISIBLE | BS_AUTORADIOBUTTON,
		     CRect(40, 40, 120, 60), this, 0x12);
    rdoMedium->Create(_T("Medium"),
             	      WS_CHILD | WS_VISIBLE | BS_AUTORADIOBUTTON,
             	      CRect(40, 70, 120, 100), this, 0x14);
    rdoLarge->Create(_T("Large"),
	             WS_CHILD | WS_VISIBLE | BS_AUTORADIOBUTTON,
	             CRect(40, 100, 120, 140), this, 0x16);

    return 0;
}

While using the radio buttons, the user is presented with the controls and requested to select one. To make a selection, the user must click the desired choice. The control selected fills its circle with a (big) dot. To programmatically change the state of a radio button, you have various options.

The easiest way to select a radio button consists of calling the CWnd::CheckRadioButton() member function (actually, you should call this member function as CDialog::CheckRadioButton()). Its syntax is:

void CheckRadioButton(int nIDFirstButton,
 		      int nIDLastButton,
		      int nIDCheckButton);

To use this member function, you must know the identifiers of the radio buttons involved. The nIDFirstButton is the identifier of the first radio button of the group. The nIDLastButton is the identifier of the last radio button of the group. The last argument, nIDCheckButton is the identifier of the radio button that must be selected. Here is an example:

void CExerciseDlg::OnBtnSelect2() 
{
    // TODO: Add your control notification handler code here
    CheckRadioButton(IDC_RADIO1, IDC_RADIO3, IDC_RADIO3);
}

To change the state of a radio button, you can call the CButton::SetCheck() member function. Its syntax is:

void SetCheck(int nCheck);

The nCheck value indicates how to fill the control's circle. To fill it with the selection dot, pass the value of 0. To deselect a radio button, pass the argument as 1. Here is an example:

void CExerciseDlg::OnBtnSelect2()
{
    // TODO: Add your control notification handler code here
    CButton *btnSecond;

    btnSecond = reinterpret_cast<CButton *>(GetDlgItem(IDC_RADIO2));
    btnSecond->SetCheck(1);
}

To find out what radio button of a group is selected, you can call the CWnd::GetCheckedRadioButton(). Its syntax is:

int GetCheckedRadioButton( int nIDFirstButton, int nIDLastButton );

When calling this member function, you must specify the identifier of the first radio button of the group as nIDFirstButton and the identifier of the last radio button of the group as nIDLastButton. The member function returns the identifier of the radio button whose circle is filled.

Alternatively, to find the selected radio button, call the CButton::GetCheck() member function. Its syntax is:

int GetCheck( ) const;

This member function returns 0 if the radio button is not selected. Otherwise, it returns 1 if the radio button is selected.

If you want to want to find whether a particular radio button is currently selected, you can call the CWnd::IsDlgButtonChecked() member function. Its syntax:

UINT IsDlgButtonChecked(int nIDButton) const;

When calling this member function, pass the identifier of the radio button as the nIDButton argument. This member function will check the state of the radio button. If the radio button is selected, the member function will return 1. If the radio button is not selected, the member function returns 0.

Because a radio is first of all a control of CButton type, when it is clicked, it generates the BN_CLICKED message. You can use this message to take action in response to the user's.

We have mentioned already that a control can have two types of variables: Control or Value. For a radio button, you can declare or add either a CButton or a regular C++ variable. If you decide to use a CButton variable, you can call the necessary member function to take advantage of the class. On the other hand, if you want to use a value instead, you can add a variable for only the first radio button of the group, the radio button that has the Group property set to true. The variable should be an integer, such as int. In such a case, each radio button of the group can be referred to by a number. The first radio button of the group would have the index 0, the second would be 1, etc.

Here is an example:

Header File

// ExerciseDlg.h : header file
//

#pragma once

// CExerciseDlg dialog
class CExerciseDlg : public CDialogEx
{
// Construction
public:
	CExerciseDlg(CWnd* pParent = NULL);	// standard constructor

// Dialog Data
	enum { IDD = IDD_CONTROLS_DIALOG };

	protected:
	virtual void DoDataExchange(CDataExchange* pDX);	// DDX/DDV support


// Implementation
protected:
	HICON m_hIcon;

	// Generated message map functions
	virtual BOOL OnInitDialog();
	afx_msg void OnPaint();
	afx_msg HCURSOR OnQueryDragIcon();
	DECLARE_MESSAGE_MAP()

public:
	int m_Gender;
	CString m_Value;
	afx_msg void OnBnClickedMale();
	afx_msg void OnBnClickedFemale();
	afx_msg void OnBnClickedDontKnow();
};

Source File

Let the// ExerciseDlg.cpp : implementation file
//

#include "stdafx.h"
#include "Controls.h"
#include "ExerciseDlg.h"
#include "afxdialogex.h"

#ifdef _DEBUG
#define new DEBUG_NEW
#endif

// CExerciseDlg dialog

CExerciseDlg::CExerciseDlg(CWnd* pParent /*=NULL*/)
	: CDialogEx(CExerciseDlg::IDD, pParent), m_Gender(0), m_Value(_T(""))
{
	m_hIcon = AfxGetApp()->LoadIcon(IDR_MAINFRAME);
}

void CExerciseDlg::DoDataExchange(CDataExchange* pDX)
{
	CDialogEx::DoDataExchange(pDX);
	DDX_Text(pDX, IDC_VALUE, m_Value);
}

BEGIN_MESSAGE_MAP(CExerciseDlg, CDialogEx)
	ON_WM_PAINT()
	ON_WM_QUERYDRAGICON()
	ON_BN_CLICKED(IDC_MALE, &CExerciseDlg::OnBnClickedMale)
	ON_BN_CLICKED(IDC_FEMALE, &CExerciseDlg::OnBnClickedFemale)
	ON_BN_CLICKED(IDC_DONT_KNOW, &CExerciseDlg::OnBnClickedDontKnow)
END_MESSAGE_MAP()

// CExerciseDlg message handlers

BOOL CExerciseDlg::OnInitDialog()
{
	CDialogEx::OnInitDialog();

	// Set the icon for this dialog.  The framework does this automatically
	//  when the application's main window is not a dialog
	SetIcon(m_hIcon, TRUE);			// Set big icon
	SetIcon(m_hIcon, FALSE);		// Set small icon

	// TODO: Add extra initialization here

	return TRUE;  // return TRUE  unless you set the focus to a control
}

// If you add a minimize button to your dialog, you will need the code below
//  to draw the icon.  For MFC applications using the document/view model,
//  this is automatically done for you by the framework.

void CExerciseDlg::OnPaint()
{
	if (IsIconic())
	{
		CPaintDC dc(this); // device context for painting

		SendMessage(WM_ICONERASEBKGND,
			    reinterpret_cast<WPARAM>(dc.GetSafeHdc()), 0);

		// Center icon in client rectangle
		int cxIcon = GetSystemMetrics(SM_CXICON);
		int cyIcon = GetSystemMetrics(SM_CYICON);
		CRect rect;
		GetClientRect(&rect);
		int x = (rect.Width() - cxIcon + 1) / 2;
		int y = (rect.Height() - cyIcon + 1) / 2;

		// Draw the icon
		dc.DrawIcon(x, y, m_hIcon);
	}
	else
	{
		CDialogEx::OnPaint();
	}
}

// The system calls this function to obtain the cursor to display while the user drags
//  the minimized window.
HCURSOR CExerciseDlg::OnQueryDragIcon()
{
	return static_cast<HCURSOR>(m_hIcon);
}

void CExerciseDlg::OnBnClickedMale()
{
	// TODO: Add your control notification handler code here
	m_Value = _T("Man");
	UpdateData(FALSE);
}

void CExerciseDlg::OnBnClickedFemale()
{
	// TODO: Add your control notification handler code here
	m_Value = _T("Woman");
	UpdateData(FALSE);
}

void CExerciseDlg::OnBnClickedDontKnow()
{
	// TODO: Add your control notification handler code here
	m_Value = _T("Unknown");
	UpdateData(FALSE);
}

1. On the dialog box, double-click the Addition radio button
2. Implement its event as follows:

   void COperationsDlg::OnBnClickedAddition()
   {
   	// TODO: Add your control notification handler code here
   	UpdateData();
   
   	m_Result = m_Operand1 + m_Operand2;
   
   	UpdateData(FALSE);
   }

3. Return to the dialog box and double-click the Subtraction radio button
4. Implement its event as follows:

   void COperationsDlg::OnBnClickedSubtraction()
   {
   	// TODO: Add your control notification handler code here
   	UpdateData();
   	m_Result = m_Operand1 - m_Operand2;
   	UpdateData(FALSE);
   }

5. Return to the dialog box and double-click the Multiplication radio button
6. Implement its event as follows:

   void COperationsDlg::OnBnClickedMultiplication()
   {
   	// TODO: Add your control notification handler code here
   	UpdateData();
   	m_Result = m_Operand1 * m_Operand2;
   	UpdateData(FALSE);
   }

7. Return to the dialog box and double-click the Division radio button
8. Implement its event as follows:

   void COperationsDlg::OnBnClickedDivision()
   {
   	// TODO: Add your control notification handler code here
   	UpdateData();
   	m_Result = m_Operand1 / m_Operand2;
   	UpdateData(FALSE);
   }

9. To execute the application to test the radio buttons, press F5
10. Enter some values in the edit boxes and click the radio buttons
     
    
     
    
     
    
     
    
11. Close the dialog box and return to your programming environment

For either the user or the programmer, radio buttons must behave as entities of one group. When you freshly add radio buttons to a host, they are created as a group. If your dialog box will be made of only a few radio buttons, you may not need to do much. Imagine you want to create a dialog box with more than one set of radio buttons. In this case, you must separate them into groups. To do that, set the Group property of each new button of a group to True. To do this programmatically, add the WS_GROUP style to the CButton object.

Imagine you will use two sets of group buttons in a dialog box. Add the first radio button and set its Group property to True or add the WS_GROUP value to its style. Then, add the other radio buttons of the set but set their Group property to False or do not add the WS_GROUP value to their styles.

When starting the new set, add a new radio button and set its Group property to True. Add the other radio buttons with the Group property set to False or without the WS_GROUP style.

1. To start a new application, on the main menu, click File -> New Project...
2. In the middle list, click MFC Application and set the name to ClarksvilleIceScream1
3. Press Enter
4. In the first page of the MFC Application Wizard, click Next
5. In the second page, click Dialog Based and click Next
6. Click Finish
7. Design the dialog box as follows:
    

   Control  Caption Group Box Flavors  Radio Button Vanilla Radio Button Cream of Cocoa Radio Button Chocolate Chip Radio Button Butter Pecan Radio Button Chunky Butter Radio Button Strawberry Vanilla Radio Button Chocolate Cookies Group Box Containers Radio Button Cup Radio Button Cone Radio Button Bowl Group Box Ingredients Radio Button None Radio Button M && M Radio Button Mixed Nuts Group Box Scoops Radio Button One Radio Button Two Radio Button Three

8. To execute the application, press F5
9. Click the radio buttons from different group boxes and notice that all radio buttons seem to belong to the same group
10. Close the dialog box and return to your programming environment
11. On the dialog box, click the Vanilla radio button
12. In the Properties window, double-click Group to set its value to True
13. On the dialog box, click the Cup radio button
14. In the Properties window, double-click Group to set its value to True
15. On the dialog box, click the None radio button
16. In the Properties window, double-click Group to set its value to True
17. On the dialog box, click the One radio button
18. In the Properties window, double-click Group to set its value to True
19. Press F5 to execute the application
20. Click the radio buttons in different sections
21. Close the dialog box and return to your programming environment