如何用qt的mainwindiw编写一个计算器代码

以下是一个简单的计算器代码示例，使用 Qt 的 QMainWindow 类：

#include <QMainWindow>
#include <QGridLayout>
#include <QLineEdit>
#include <QPushButton>

class Calculator : public QMainWindow {
  Q_OBJECT

public:
  Calculator(QWidget *parent = nullptr) : QMainWindow(parent) {
    QWidget *centralWidget = new QWidget(this);
    setCentralWidget(centralWidget);

    QGridLayout *gridLayout = new QGridLayout(centralWidget);
    QLineEdit *lineEdit = new QLineEdit(centralWidget);
    gridLayout->addWidget(lineEdit, 0, 0, 1, 4);

    QPushButton *button0 = new QPushButton("0", centralWidget);
    QPushButton *button1 = new QPushButton("1", centralWidget);
    QPushButton *button2 = new QPushButton("2", centralWidget);
    QPushButton *button3 = new QPushButton("3", centralWidget);
    QPushButton *button4 = new QPushButton("4", centralWidget);
    QPushButton *button5 = new QPushButton("5", centralWidget);
    QPushButton *button6 = new QPushButton("6", centralWidget);
    QPushButton *button7 = new QPushButton("7", centralWidget);
    QPushButton *button8 = new QPushButton("8", centralWidget);
    QPushButton *button9 = new QPushButton("9", centralWidget);
    QPushButton *buttonPlus = new QPushButton("+", centralWidget);
    QPushButton *buttonMinus = new QPushButton("-", centralWidget);
    QPushButton *buttonMultiply = new QPushButton("*", centralWidget);
    QPushButton *buttonDivide = new QPushButton("/", centralWidget);
    QPushButton *buttonEquals = new QPushButton("=", centralWidget);
    gridLayout->addWidget(button7, 1, 0);
    gridLayout->addWidget(button8, 1, 1);
    gridLayout->addWidget(button9, 1, 2);
    gridLayout->addWidget(buttonPlus, 1, 3);
    gridLayout->addWidget(button4, 2, 0);
    gridLayout->addWidget(button5, 2, 1);
    gridLayout->addWidget(button6, 2, 2);
    gridLayout->addWidget(buttonMinus, 2, 3);
    gridLayout->addWidget(button1, 3, 0);
    gridLayout->addWidget(button2, 3, 1);
    gridLayout->addWidget(button3, 3, 2);
    gridLayout->addWidget(buttonMultiply, 3, 3);
    gridLayout->addWidget(button0, 4, 0, 1, 2);
    gridLayout->addWidget(buttonDivide, 4, 2);
    gridLayout->addWidget(buttonEquals, 4, 3);

    connect(button0, &QPushButton::clicked, this, [=] { addDigitToLineEdit("0"); });
    connect(button1, &QPushButton::clicked, this, [=] { addDigitToLineEdit("1"); });
    connect(button2, &QPushButton::clicked, this, [=] { addDigitToLineEdit("2"); });
    connect(button3, &QPushButton::clicked, this, [=] { addDigitToLineEdit("3"); });
    connect(button4, &QPushButton::clicked, this, [=] { addDigitToLineEdit("4"); });
    connect(button5, &QPushButton::clicked, this, [=] { addDigitToLineEdit("5"); });
    connect(button6, &QPushButton::clicked, this, [=] { addDigitToLineEdit("6"); });
    connect(button7, &QPushButton::clicked, this, [=] { addDigitToLineEdit("7"); });
    connect(button8, &QPushButton::clicked, this, [=] { addDigitToLineEdit("8"); });
    connect(button9, &QPushButton::clicked, this, [=] { addDigitToLineEdit("9"); });
    connect(buttonPlus, &QPushButton::clicked, this, [=] { addOperatorToLineEdit("+"); });
    connect(buttonMinus, &QPushButton::clicked, this, [=] { addOperatorToLineEdit("-"); });
    connect(buttonMultiply, &QPushButton::clicked, this, [=] { addOperatorToLineEdit("*"); });
    connect(buttonDivide, &QPushButton::clicked, this, [=] { addOperatorToLineEdit("/"); });
    connect(buttonEquals, &QPushButton::clicked, this, [=] { evaluateExpression(lineEdit->text()); });
  }

private:
  void addDigitToLineEdit(const QString &digit) {
    QLineEdit *lineEdit = centralWidget()->findChild<QLineEdit *>();
    lineEdit->insert(digit);
  }

  void addOperatorToLineEdit(const QString &op) {
    QLineEdit *lineEdit = centralWidget()->findChild<QLineEdit *>();
    lineEdit->insert(op);
  }

  void evaluateExpression(const QString &expression) {
    QLineEdit *lineEdit = centralWidget()->findChild<QLineEdit *>();
    lineEdit->setText(QString::number(eval(expression)));
  }

  int eval(const QString &expression) {
    // TODO: Implement expression evaluation.
    return 0;
  }
};

int main(int argc, char *argv[]) {
  QApplication app(argc, argv);
  Calculator calculator;
  calculator.show();
  return app.exec();
}

#include "main.moc"

该代码创建了一个具有数字按钮、运算符按钮和等号按钮的简单计算器界面。当用户单击数字或运算符按钮时，该按钮的文本将插入到 QLineEdit 中。当用户单击等号按钮时，该表达式将计算并在 QLineEdit 中显示结果。

请注意，该代码尚未实现表达式求值的算法。你需要编写一个 eval() 函数来实现它，这超出了本答案的范围。