qt如何实现计算器负数加减

在Qt中实现计算器负数加减，可以通过以下步骤实现：

1. 定义一个变量用于存储当前输入的数字，例如定义一个double类型的变量num。

2. 对于输入的数字，如果是负数，可以在数字前面加上负号“-”，例如输入“-2”。

3. 对于加法和减法操作，需要判断当前数字是否为负数，如果是负数，则需要将操作符和下一个数字一起加上括号“()”，例如：(-2)+3 或 (-2)-3。

4. 最后进行计算时，需要将括号去除，并将负数加上符号“-”，例如：(-2)+3 等价于 -2+3。

下面是一个简单的实现示例：

#include <QHBoxLayout>
#include <QVBoxLayout>
#include <QLineEdit>
#include <QPushButton>

class Calculator : public QWidget
{
    Q_OBJECT
public:
    Calculator(QWidget *parent = nullptr) : QWidget(parent)
    {
        // 设置界面布局
        QVBoxLayout *layout = new QVBoxLayout(this);
        QHBoxLayout *hLayout1 = new QHBoxLayout();
        QHBoxLayout *hLayout2 = new QHBoxLayout();
        QHBoxLayout *hLayout3 = new QHBoxLayout();
        QHBoxLayout *hLayout4 = new QHBoxLayout();
        layout->addLayout(hLayout1);
        layout->addLayout(hLayout2);
        layout->addLayout(hLayout3);
        layout->addLayout(hLayout4);

        // 添加数字和操作符按钮
        QPushButton *btn0 = new QPushButton(tr("0"));
        QPushButton *btn1 = new QPushButton(tr("1"));
        QPushButton *btn2 = new QPushButton(tr("2"));
        QPushButton *btn3 = new QPushButton(tr("3"));
        QPushButton *btn4 = new QPushButton(tr("4"));
        QPushButton *btn5 = new QPushButton(tr("5"));
        QPushButton *btn6 = new QPushButton(tr("6"));
        QPushButton *btn7 = new QPushButton(tr("7"));
        QPushButton *btn8 = new QPushButton(tr("8"));
        QPushButton *btn9 = new QPushButton(tr("9"));
        QPushButton *btnAdd = new QPushButton(tr("+"));
        QPushButton *btnSub = new QPushButton(tr("-"));
        QPushButton *btnEqual = new QPushButton(tr("="));
        QPushButton *btnClear = new QPushButton(tr("C"));
        hLayout1->addWidget(btn7);
        hLayout1->addWidget(btn8);
        hLayout1->addWidget(btn9);
        hLayout1->addWidget(btnAdd);
        hLayout2->addWidget(btn4);
        hLayout2->addWidget(btn5);
        hLayout2->addWidget(btn6);
        hLayout2->addWidget(btnSub);
        hLayout3->addWidget(btn1);
        hLayout3->addWidget(btn2);
        hLayout3->addWidget(btn3);
        hLayout3->addWidget(btnEqual);
        hLayout4->addWidget(btn0);
        hLayout4->addWidget(btnClear);

        // 添加文本框
        m_lineEdit = new QLineEdit();
        m_lineEdit->setAlignment(Qt::AlignRight);
        layout->addWidget(m_lineEdit);

        // 连接信号和槽
        connect(btn0, &QPushButton::clicked, this, &Calculator::onNumButtonClicked);
        connect(btn1, &QPushButton::clicked, this, &Calculator::onNumButtonClicked);
        connect(btn2, &QPushButton::clicked, this, &Calculator::onNumButtonClicked);
        connect(btn3, &QPushButton::clicked, this, &Calculator::onNumButtonClicked);
        connect(btn4, &QPushButton::clicked, this, &Calculator::onNumButtonClicked);
        connect(btn5, &QPushButton::clicked, this, &Calculator::onNumButtonClicked);
        connect(btn6, &QPushButton::clicked, this, &Calculator::onNumButtonClicked);
        connect(btn7, &QPushButton::clicked, this, &Calculator::onNumButtonClicked);
        connect(btn8, &QPushButton::clicked, this, &Calculator::onNumButtonClicked);
        connect(btn9, &QPushButton::clicked, this, &Calculator::onNumButtonClicked);
        connect(btnAdd, &QPushButton::clicked, this, &Calculator::onOperatorButtonClicked);
        connect(btnSub, &QPushButton::clicked, this, &Calculator::onOperatorButtonClicked);
        connect(btnEqual, &QPushButton::clicked, this, &Calculator::onEqualButtonClicked);
        connect(btnClear, &QPushButton::clicked, this, &Calculator::onClearButtonClicked);
    }

private slots:
    void onNumButtonClicked()
    {
        QPushButton *btn = qobject_cast<QPushButton*>(sender());
        if(btn)
        {
            QString text = btn->text();
            m_lineEdit->setText(m_lineEdit->text() + text);
        }
    }

    void onOperatorButtonClicked()
    {
        QPushButton *btn = qobject_cast<QPushButton*>(sender());
        if(btn)
        {
            QString text = btn->text();
            m_lineEdit->setText(m_lineEdit->text() + text);
        }
    }

    void onEqualButtonClicked()
    {
        QString input = m_lineEdit->text();
        QRegExp regExp("(-?[0-9.]+)([+-])(-?[0-9.]+)");
        if(regExp.indexIn(input) != -1)
        {
            double num1 = regExp.cap(1).toDouble();
            QString op = regExp.cap(2);
            double num2 = regExp.cap(3).toDouble();

            double result = 0;
            if(op == "+")
            {
                result = num1 + num2;
            }
            else if(op == "-")
            {
                result = num1 - num2;
            }

            m_lineEdit->setText(QString::number(result));
        }
    }

    void onClearButtonClicked()
    {
        m_lineEdit->clear();
    }

private:
    QLineEdit *m_lineEdit;
};

在上面的实现中，我们使用了QRegExp来匹配输入的数字和操作符，并进行计算。其中，正则表达式“(-?[0-9.]+)([+-])(-?[0-9.]+)”中的“-?”表示可选的负号，[0-9.]+表示匹配数字，[+-]表示匹配加号或减号。