编写MFC计算器

以下是一个简单的 MFC 计算器的代码：

首先，可以使用 MFC 库中的 CWnd 类来创建窗口和处理事件。我们需要创建一个派生自 CWnd 的类，我们称之为 CCalculatorWnd。

CCalculatorWnd.h 文件：

#pragma once

class CCalculatorWnd : public CWnd
{
public:
    CCalculatorWnd();

protected:
    afx_msg void OnChar(UINT nChar, UINT nRepCnt, UINT nFlags);
    afx_msg void OnLButtonDown(UINT nFlags, CPoint point);
    afx_msg void OnPaint();

    DECLARE_MESSAGE_MAP()
private:
    CString m_strDisplay;
    double m_dResult;
    CString m_strOperator;
    BOOL m_bDecimal;
    BOOL m_bNewNumber;
    BOOL m_bError;
};

CCalculatorWnd.cpp 文件：

#include "stdafx.h"
#include "Calculator.h"
#include "CalculatorWnd.h"

#ifdef _DEBUG
#define new DEBUG_NEW
#endif

CCalculatorWnd::CCalculatorWnd()
{
    m_strDisplay = _T("0");
    m_dResult = 0.0;
    m_strOperator = _T("");
    m_bDecimal = FALSE;
    m_bNewNumber = TRUE;
    m_bError = FALSE;
}

BEGIN_MESSAGE_MAP(CCalculatorWnd, CWnd)
    ON_WM_CHAR()
    ON_WM_LBUTTONDOWN()
    ON_WM_PAINT()
END_MESSAGE_MAP()

void CCalculatorWnd::OnChar(UINT nChar, UINT nRepCnt, UINT nFlags)
{
    if (m_bError)
    {
        m_strDisplay = _T("0");
        m_dResult = 0.0;
        m_strOperator = _T("");
        m_bDecimal = FALSE;
        m_bNewNumber = TRUE;
        m_bError = FALSE;
    }

    switch (nChar)
    {
    case '0':
    case '1':
    case '2':
    case '3':
    case '4':
    case '5':
    case '6':
    case '7':
    case '8':
    case '9':
        if (m_bNewNumber)
        {
            m_strDisplay = _T("");
            m_bNewNumber = FALSE;
        }

        m_strDisplay += nChar;
        break;

    case '.':
        if (m_bNewNumber)
        {
            m_strDisplay = _T("0");
            m_bNewNumber = FALSE;
        }

        if (!m_bDecimal)
        {
            m_strDisplay += nChar;
            m_bDecimal = TRUE;
        }

        break;

    case '+':
    case '-':
    case '*':
    case '/':
        if (!m_strOperator.IsEmpty())
        {
            OnLButtonDown(0, CPoint(0, 0));
        }

        m_bNewNumber = TRUE;
        m_bDecimal = FALSE;
        m_strOperator = nChar;
        break;

    case '=':
        OnLButtonDown(0, CPoint(0, 0));
        m_strOperator = _T("");
        break;

    case '\b':
        if (m_strDisplay.GetLength() > 1)
        {
            m_strDisplay = m_strDisplay.Left(m_strDisplay.GetLength() - 1);
        }
        else
        {
            m_strDisplay = _T("0");
            m_bNewNumber = TRUE;
        }

        break;

    case 'c':
    case 'C':
        m_strDisplay = _T("0");
        m_dResult = 0.0;
        m_strOperator = _T("");
        m_bDecimal = FALSE;
        m_bNewNumber = TRUE;
        break;
    }

    Invalidate();
}

void CCalculatorWnd::OnLButtonDown(UINT nFlags, CPoint point)
{
    double dOperand = _wtof(m_strDisplay);

    if (m_strOperator.IsEmpty())
    {
        m_dResult = dOperand;
    }
    else
    {
        switch (m_strOperator[0])
        {
        case '+':
            m_dResult += dOperand;
            break;

        case '-':
            m_dResult -= dOperand;
            break;

        case '*':
            m_dResult *= dOperand;
            break;

        case '/':
            if (dOperand == 0.0)
            {
                m_strDisplay = _T("Error");
                m_bError = TRUE;
                return;
            }
            else
            {
                m_dResult /= dOperand;
            }

            break;
        }
    }

    CString strResult;
    strResult.Format(_T("%g"), m_dResult);
    m_strDisplay = strResult;
    m_bNewNumber = TRUE;
    m_bDecimal = FALSE;
}

void CCalculatorWnd::OnPaint()
{
    CPaintDC dc(this);
    CRect rcClient;
    GetClientRect(&rcClient);

    CBrush brush;
    brush.CreateSolidBrush(RGB(255, 255, 255));
    dc.FillRect(&rcClient, &brush);

    CFont font;
    font.CreateFont(20, 0, 0, 0, FW_NORMAL, FALSE, FALSE, FALSE, DEFAULT_CHARSET,
        OUT_DEFAULT_PRECIS, CLIP_DEFAULT_PRECIS, DEFAULT_QUALITY,
        DEFAULT_PITCH | FF_SWISS, _T("Arial"));
    dc.SelectObject(&font);

    rcClient.DeflateRect(5, 5);
    dc.DrawText(m_strDisplay, &rcClient, DT_RIGHT | DT_SINGLELINE | DT_VCENTER);
}

最后，在主函数中创建窗口并运行：

#include "stdafx.h"
#include "Calculator.h"
#include "CalculatorWnd.h"

#ifdef _DEBUG
#define new DEBUG_NEW
#endif

int APIENTRY _tWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPTSTR lpCmdLine, int nCmdShow)
{
    UNREFERENCED_PARAMETER(hPrevInstance);
    UNREFERENCED_PARAMETER(lpCmdLine);

    AfxWinInit(hInstance, NULL, ::GetCommandLine(), 0);
    CCalculatorWnd wnd;
    wnd.Create(NULL, _T("Calculator"), WS_OVERLAPPEDWINDOW, CRect(0, 0, 200, 200));
    wnd.ShowWindow(nCmdShow);
    wnd.UpdateWindow();
    MSG msg;
    while (::GetMessage(&msg, NULL, 0, 0))
    {
        ::TranslateMessage(&msg);
        ::DispatchMessage(&msg);
    }

    return (int)msg.wParam;
}

现在，你就可以编译和运行代码，得到一个简单的 MFC 计算器。