用qt制作一个可以绘制一次函数和二次函数的程序 要有坐标轴 要有刻度 要有正负轴 函数的各项系数以及常数由使用者输入

以下是一个简单的基于Qt的程序，可以绘制一次函数和二次函数，并且由用户输入函数的系数和常数，同时包含坐标轴、刻度和正负轴。请注意，此程序仅作为示例，可能需要您进行修改以满足您的实际需求。

#include <QtWidgets>

class GraphWidget : public QWidget
{
public:
    GraphWidget(QWidget *parent = nullptr)
        : QWidget(parent)
    {
        // 初始化参数
        m_a = 1.0;
        m_b = 0.0;
        m_c = 0.0;
        m_xMin = -10.0;
        m_xMax = 10.0;
        m_yMin = -10.0;
        m_yMax = 10.0;

        // 设置窗口大小
        setFixedSize(500, 500);
    }

    void setCoefficients(double a, double b, double c)
    {
        m_a = a;
        m_b = b;
        m_c = c;
    }

    void setRange(double xMin, double xMax, double yMin, double yMax)
    {
        m_xMin = xMin;
        m_xMax = xMax;
        m_yMin = yMin;
        m_yMax = yMax;
    }

protected:
    void paintEvent(QPaintEvent *event) override
    {
        Q_UNUSED(event);

        QPainter painter(this);

        // 绘制坐标轴
        painter.drawLine(0, height() / 2, width(), height() / 2);
        painter.drawLine(width() / 2, 0, width() / 2, height());

        // 绘制刻度
        double xStep = (m_xMax - m_xMin) / 10.0;
        double yStep = (m_yMax - m_yMin) / 10.0;
        QFont font;
        font.setPointSize(8);
        painter.setFont(font);
        for (int i = 1; i < 10; i++) {
            int x = width() * i / 10;
            int y = height() * i / 10;
            painter.drawLine(x, height() / 2 - 5, x, height() / 2 + 5);
            painter.drawText(x - 10, height() / 2 + 15, QString::number(m_xMin + i * xStep));
            painter.drawLine(width() / 2 - 5, y, width() / 2 + 5, y);
            painter.drawText(width() / 2 + 10, y + 5, QString::number(m_yMax - i * yStep));
        }

        // 绘制正负轴
        painter.setPen(Qt::DashLine);
        painter.drawLine(0, height() / 2 - (m_yMin / (m_yMax - m_yMin)) * height(),
                         width(), height() / 2 - (m_yMin / (m_yMax - m_yMin)) * height());
        painter.drawLine(width() / 2 + (m_xMin / (m_xMax - m_xMin)) * width(), 0,
                         width() / 2 + (m_xMin / (m_xMax - m_xMin)) * width(), height());

        // 绘制函数
        painter.setPen(Qt::SolidLine);
        painter.setBrush(Qt::NoBrush);
        QPainterPath path;
        double xStepSize = (m_xMax - m_xMin) / width();
        for (int i = 0; i < width(); i++) {
            double x = m_xMin + i * xStepSize;
            double y = m_a * x * x + m_b * x + m_c;
            int xPixel = i;
            int yPixel = height() / 2 - (y / (m_yMax - m_yMin)) * height();
            if (i == 0) {
                path.moveTo(xPixel, yPixel);
            } else {
                path.lineTo(xPixel, yPixel);
            }
        }
        painter.drawPath(path);
    }

private:
    double m_a;
    double m_b;
    double m_c;
    double m_xMin;
    double m_xMax;
    double m_yMin;
    double m_yMax;
};

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

        QVBoxLayout *layout = new QVBoxLayout(centralWidget);

        // 创建输入框和按钮
        QLineEdit *aLineEdit = new QLineEdit;
        QLineEdit *bLineEdit = new QLineEdit;
        QLineEdit *cLineEdit = new QLineEdit;
        QLineEdit *xMinLineEdit = new QLineEdit;
        QLineEdit *xMaxLineEdit = new QLineEdit;
        QLineEdit *yMinLineEdit = new QLineEdit;
        QLineEdit *yMaxLineEdit = new QLineEdit;
        QPushButton *plotButton = new QPushButton(tr("Plot"));

        // 创建绘图窗口
        GraphWidget *graphWidget = new GraphWidget;

        // 将控件添加到布局中
        layout->addWidget(new QLabel(tr("a:")));
        layout->addWidget(aLineEdit);
        layout->addWidget(new QLabel(tr("b:")));
        layout->addWidget(bLineEdit);
        layout->addWidget(new QLabel(tr("c:")));
        layout->addWidget(cLineEdit);
        layout->addWidget(new QLabel(tr("xMin:")));
        layout->addWidget(xMinLineEdit);
        layout->addWidget(new QLabel(tr("xMax:")));
        layout->addWidget(xMaxLineEdit);
        layout->addWidget(new QLabel(tr("yMin:")));
        layout->addWidget(yMinLineEdit);
        layout->addWidget(new QLabel(tr("yMax:")));
        layout->addWidget(yMaxLineEdit);
        layout->addWidget(plotButton);
        layout->addWidget(graphWidget);

        // 连接按钮的点击事件
        connect(plotButton, &QPushButton::clicked, [=]() {
            bool ok;
            double a = aLineEdit->text().toDouble(&ok);
            if (!ok) {
                QMessageBox::warning(this, tr("Error"), tr("Invalid a value"));
                return;
            }
            double b = bLineEdit->text().toDouble(&ok);
            if (!ok) {
                QMessageBox::warning(this, tr("Error"), tr("Invalid b value"));
                return;
            }
            double c = cLineEdit->text().toDouble(&ok);
            if (!ok) {
                QMessageBox::warning(this, tr("Error"), tr("Invalid c value"));
                return;
            }
            double xMin = xMinLineEdit->text().toDouble(&ok);
            if (!ok) {
                QMessageBox::warning(this, tr("Error"), tr("Invalid xMin value"));
                return;
            }
            double xMax = xMaxLineEdit->text().toDouble(&ok);
            if (!ok) {
                QMessageBox::warning(this, tr("Error"), tr("Invalid xMax value"));
                return;
            }
            double yMin = yMinLineEdit->text().toDouble(&ok);
            if (!ok) {
                QMessageBox::warning(this, tr("Error"), tr("Invalid yMin value"));
                return;
            }
            double yMax = yMaxLineEdit->text().toDouble(&ok);
            if (!ok) {
                QMessageBox::warning(this, tr("Error"), tr("Invalid yMax value"));
                return;
            }
            graphWidget->setCoefficients(a, b, c);
            graphWidget->setRange(xMin, xMax, yMin, yMax);
            graphWidget->update();
        });
    }
};

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

在此程序中，我们创建了一个名为`GraphWidget`的自定义QWidget类，用于绘制坐标轴、刻度、正负轴和函数。我们还创建了一个名为`MainWindow`的主窗口，包含输入框和按钮，用于让用户输入函数的系数和常数，以及用于显示绘图的`GraphWidget`实例。

在`GraphWidget`类中，我们重载了`paintEvent()`函数，用于绘制坐标轴、刻度、正负轴和函数。在`MainWindow`类中，我们使用Qt的布局管理器将输入框、按钮和`GraphWidget`添加到主窗口中，并将按钮的点击事件连接到绘图函数中。