用c++写一个Windows系统的图片查看器程序。

好的，我可以为您提供一个简单的 Windows 图片查看器程序的代码示例：

#include <windows.h>

LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
    static TCHAR szAppName[] = TEXT("Image Viewer");
    HWND hwnd;
    MSG msg;
    WNDCLASS wndclass;

    wndclass.style = CS_HREDRAW | CS_VREDRAW;
    wndclass.lpfnWndProc = WndProc;
    wndclass.cbClsExtra = 0;
    wndclass.cbWndExtra = 0;
    wndclass.hInstance = hInstance;
    wndclass.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    wndclass.hCursor = LoadCursor(NULL, IDC_ARROW);
    wndclass.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);
    wndclass.lpszMenuName = NULL;
    wndclass.lpszClassName = szAppName;

    if (!RegisterClass(&wndclass))
    {
        MessageBox(NULL, TEXT("This program requires Windows NT!"), szAppName, MB_ICONERROR);
        return 0;
    }

    hwnd = CreateWindow(szAppName, TEXT("Image Viewer"), WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,
        NULL, NULL, hInstance, NULL);

    ShowWindow(hwnd, nCmdShow);
    UpdateWindow(hwnd);

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

    return msg.wParam;
}

LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    static HBITMAP hBitmap;
    static int cxClient, cyClient;
    HDC hdc, hdcMem;
    PAINTSTRUCT ps;
    RECT rect;

    switch (message)
    {
    case WM_CREATE:
        hBitmap = (HBITMAP)LoadImage(NULL, TEXT("image.bmp"), IMAGE_BITMAP, 0, 0, LR_LOADFROMFILE);
        if (hBitmap == NULL)
        {
            MessageBox(hwnd, TEXT("Could not load image.bmp!"), TEXT("Error"), MB_ICONERROR);
            return -1;
        }
        return 0;

    case WM_SIZE:
        cxClient = LOWORD(lParam);
        cyClient = HIWORD(lParam);
        return 0;

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

        hdcMem = CreateCompatibleDC(hdc);
        SelectObject(hdcMem, hBitmap);

        GetClientRect(hwnd, &rect);
        StretchBlt(hdc, 0, 0, cxClient, cyClient, hdcMem, 0, 0, 640, 480, SRCCOPY);

        DeleteDC(hdcMem);

        EndPaint(hwnd, &ps);
        return 0;

    case WM_DESTROY:
        DeleteObject(hBitmap);
        PostQuitMessage(0);
        return 0;
    }

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

这个程序使用了 Windows API 来创建一个窗口，并在窗口中显示一张图片。图片文件名为 "image.bmp"，需要放在程序所在的目录下。您可以根据自己的需要修改代码来实现更多功能。