Windows Logic

This is a discussion on Windows Logic within the Windows Programming forums, part of the Platform Specific Boards category; I'm just lightly delving into windows programming. Not exactly sure what the difference is between the windows aPI and MFC ...

  1. #1
    WDT
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    Windows Logic

    I'm just lightly delving into windows programming.
    Not exactly sure what the difference is between the windows aPI and MFC (Though I hear the MFC is quite old and it sounds to me like another layer on top of the WinAPI).
    Anyway the problem is this I am testing for the result of a message box and executing a conditional statement depending on the result, problem is the condition always seems to result to true. Anyway here's the portion of code that does that. Is there anything wrong with the logic??
    Code:
    LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
    {
    int answer; //stores the result of the message box
        switch(msg)
        {
            case WM_MBUTTONDOWN:
            case WM_LBUTTONDOWN:
            {
                char szFileName[MAX_PATH];
                HINSTANCE hInstance = GetModuleHandle(NULL);
                GetModuleFileName(hInstance, szFileName, MAX_PATH);
                FlashWindow(hwnd, TRUE);
                answer = MessageBox(hwnd, "Exit Applications Test Zone??", "Quit", MB_YESNO | MB_ICONINFORMATION);
                if (answer = IDYES) DestroyWindow(hwnd); //Always seems to result to IDYES.... Why??           
            };  
            break;
            case WM_CLOSE:
                DestroyWindow(hwnd);
            break;
            case WM_DESTROY:
                PostQuitMessage(0);
            break;
            default:
                return DefWindowProc(hwnd, msg, wParam, lParam);
        }
        return 0;
    }
    A hundred Elephants can knock down the walls of a fortress... One diseased rat can kill everyone inside

  2. #2
    Confused Magos's Avatar
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    Code:
    if (answer = IDYES)
    Probably the most common programming mistake. Replace = with ==
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  3. #3
    WDT
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    Honestly if there's one thing I hate about programming it the minor thngs that hinder such as this.... Arghh
    Thanx Magos
    A hundred Elephants can knock down the walls of a fortress... One diseased rat can kill everyone inside

  4. #4
    Even death may die... Dante Shamest's Avatar
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    I read in a book once that there's a simple way to avoid that mistake, just test the condition backwards:

    Code:
    if ( IDYES == answer )
    If you accidentally use '=' instead of '==', the compiler won't compile the following:

    Code:
    if ( IDYES = answer )
    Since IDYES is a numeric constant, you can't assign stuff to it.

  5. #5
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    The latest versions (.NET) of MSVC pick the single = sign error up.
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