按要求写c++的windows编程：按下键盘上的ctrl + R键，圆形变为正方形，按下ctrl+C键又变回圆形，如此，可实现圆和正方形间的切换

以下是实现该功能的C++代码:

#include <windows.h>

LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam);

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
    const char CLASS_NAME[] = "myWindowClass";

    WNDCLASS wc = {};

    wc.lpfnWndProc = WindowProc;
    wc.hInstance = hInstance;
    wc.lpszClassName = CLASS_NAME;

    RegisterClass(&wc);

    HWND hwnd = CreateWindowEx(
        0,
        CLASS_NAME,
        "My Window",
        WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,
        NULL,
        NULL,
        hInstance,
        NULL
    );

    if (hwnd == NULL)
    {
        return 0;
    }

    ShowWindow(hwnd, nCmdShow);

    MSG msg = {};

    while (GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    return 0;
}

LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    static bool isSquare = false;
    static HBRUSH hBrush = CreateSolidBrush(RGB(255, 0, 0)); // 红色刷子
    static HPEN hPen = CreatePen(PS_SOLID, 5, RGB(0, 0, 0)); // 黑色画笔

    switch (uMsg)
    {
    case WM_DESTROY:
        PostQuitMessage(0);
        return 0;

    case WM_PAINT:
    {
        PAINTSTRUCT ps;
        HDC hdc = BeginPaint(hwnd, &ps);

        // 创建圆形
        if (!isSquare)
        {
            SelectObject(hdc, hBrush);
            SelectObject(hdc, hPen);
            Ellipse(hdc, 50, 50, 200, 200);
        }
        // 创建正方形
        else
        {
            SelectObject(hdc, GetStockObject(WHITE_BRUSH));
            SelectObject(hdc, GetStockObject(BLACK_PEN));
            Rectangle(hdc, 50, 50, 200, 200);
        }

        EndPaint(hwnd, &ps);
    }
    return 0;

    case WM_KEYDOWN:
        if (GetKeyState(VK_CONTROL) & 0x8000) // 按下Ctrl键
        {
            if (wParam == 'R') // 按下R键
            {
                isSquare = true;
                InvalidateRect(hwnd, NULL, TRUE); // 重绘窗口
            }
            else if (wParam == 'C') // 按下C键
            {
                isSquare = false;
                InvalidateRect(hwnd, NULL, TRUE); // 重绘窗口
            }
        }
        return 0;
    }

    return DefWindowProc(hwnd, uMsg, wParam, lParam);
}

这个程序创建了一个窗口，按下键盘上的Ctrl + R键会将圆形变为正方形，按下Ctrl + C键又会将正方形变回圆形。实现的关键在于在窗口过程中检测键盘按下事件，并通过InvalidateRect函数重绘窗口来实现形状的切换。