Windows

HINSTANCE hinst;  
HWND hwndMain;

// Create the main window.  
hwndMain = CreateWindowEx( 
    0,                      // no extended styles           
    "MainWClass",           // class name                   
    "Main Window",          // window name                  
    WS_OVERLAPPEDWINDOW |   // overlapped window            
        WS_HSCROLL |        // horizontal scroll bar        
        WS_VSCROLL,         // vertical scroll bar          
    CW_USEDEFAULT,          // default horizontal position  

    CW_USEDEFAULT,          // default vertical position    
    CW_USEDEFAULT,          // default width                
    CW_USEDEFAULT,          // default height               
    (HWND) NULL,            // no parent or owner window    
    (HMENU) NULL,           // class menu used              
    hinstance,              // instance handle              
    NULL);                  // no window creation data

if (!hwndMain) 
    return FALSE; 

// Show the window using the flag specified by the program 
// that started the application, and send the application 
// a WM_PAINT message. 
ShowWindow(hwndMain, SW_SHOWDEFAULT); 
UpdateWindow(hwndMain);

#define ID_FIRSTCHILD  100  
#define ID_SECONDCHILD 101 
#define ID_THIRDCHILD  102

LONG APIENTRY MainWndProc(hwnd, uMsg, wParam, lParam) 
HWND hwnd; 
UINT uMsg; 
UINT wParam; 
LONG lParam; 
{ 
   RECT rcClient; 
   int i; 
 
   switch(uMsg) { 
      case WM_CREATE: // creating main window  
         // Create three invisible child windows. 
         for (i = 0; i < 3; i++) 
            CreateWindowEx(0, "ChildWClass", 
                 (LPCTSTR) NULL, 
                 WS_CHILD | WS_BORDER, 
                 0,0,0,0, hwnd, 
                 (HMENU) (int) (ID_FIRSTCHILD + i), 
                 hinst, NULL); 
         return 0; 

 
      case WM_SIZE:   // main window changed size 
         // Get the dimensions of the main window's client 
         // area, and enumerate the child windows. Pass the 
         // dimensions to the child windows during enumeration.
          
         GetClientRect(hwnd, &rcClient); 
         EnumChildWindows(hwnd, EnumChildProc, 
                (LPARAM) &rcClient); 
         return 0; 
   
      // Process other messages. 
      // ... 
 
   } 
   return DefWindowProc(hwnd, uMsg, wParam, lParam); 
} 

BOOL CALLBACK EnumChildProc(hwndChild, lParam) 
HWND hwndChild; 
LPARAM lParam; 
{ 
   LPRECT rcParent; 
   int i, idChild; 

 
   // Retrieve the child-window identifier. Use it to set the 
   // position of the child window. 
   idChild = GetWindowLong(hwndChild, GWL_ID);  
   if (idChild == ID_FIRSTCHILD) 
      i = 0; 
   else 
   if (idChild == ID_SECONDCHILD) 
      i = 1; 
   else 
      i = 2; 
 

   // Size and position the child window.  
   rcParent = (LPRECT) lParam; 
   MoveWindow(hwndChild, 
        (rcParent->right / 3) * i, 0, 
        rcParent->right / 3, 
        rcParent->bottom, 
        TRUE); 
 

   // Make sure the child window is visible. 
   ShowWindow(hwndChild, SW_SHOW); 
   return TRUE; 
} 

case WM_CLOSE:  
   // Create the message box. If the user clicks 
   // the Yes button, destroy the main window. 
   if (MessageBox(hwnd, szConfirm, szAppName, 
            MB_YESNOCANCEL) == IDYES) 
      DestroyWindow(hwndMain); 
   else 
      return 0;  

case WM_DESTROY: 
   // Post the WM_QUIT message to 
   // quit the application terminate. 
   PostQuitMessage(0); 
   return 0;