一个计算器程序，帮忙看看哪错了,该如何解决

//calc.h
#ifndef CALC_H
#define CALC_H

#include <QtGui/QMainWindow>
#include <QToolButton>
#include <QLineEdit>

class QToolButton;
class QLineEdit;

class calc : public QWidget
{
    Q_OBJECT

public:
    calc(QWidget *parent = 0);
    ~calc();

public slots:
    void digitClick();
    void operatClick();
    void equalClick();
    void changesignClick();
    void pointClick();
    void backspaceCk();
    void clearAll();
    void clear();
    void clearMemory();
    void readMemory();
    void setMemory();
    void addToMemory();
    void unarryClick();
    void wrong();

private:
    QLineEdit *display;
    QToolButton *digitButton[10];

    double sum;
    double memory;
    double right;
    QString ch;
    bool waitingForOperand;
};

#endif // CALC_H

//calc.cpp
#include <QtGui>
#include <cmath>
#include "calc.h"

calc::calc(QWidget *parent)
    : QWidget(parent)
{
    sum = 0.0;
    memory = 0.0;
    right = 0.0;
    ch = "";
    waitingForOperand = true;

    display = new QLineEdit("0");
    display->setReadOnly(true);
    display->setAlignment(Qt::AlignRight);
    display->setMaxLength(15);

    QFont font = display->font();
    font.setPointSize(font.pointSize() + 8);
    display->setFont(font);

    for (int i = 0; i < 10; ++i)
    {
        digitButton = new QToolButton;
        digitButton->setText(QString::number(i));
        connect(digitButton,SIGNAL(clicked()),this,SLOT(digitClick()));
    }

    QToolButton *clearMemoryBtn = new QToolButton;
    clearMemoryBtn->setText("MC");
    connect(clearMemoryBtn,SIGNAL(clicked()),this,SLOT(clearMemory()));

    QToolButton *readMemoryBtn = new QToolButton;
    readMemoryBtn->setText("MR");
    connect(readMemoryBtn,SIGNAL(clicked()),this,SLOT(readMemory()));

    QToolButton *setMemoryBtn = new QToolButton;
    setMemoryBtn->setText("MS");
    connect(setMemoryBtn,SIGNAL(clicked()),this,SLOT(setMemory()));

    QToolButton *addMemoryBtn = new QToolButton;
    addMemoryBtn->setText("M+");
    connect(addMemoryBtn,SIGNAL(clicked()),this,SLOT(addToMemory()));

    QToolButton *changeBtn = new QToolButton;
    changeBtn->setText("+/-");
    connect(changeBtn,SIGNAL(clicked()),this,SLOT(changesignClick()));

    QToolButton *pointBtn = new QToolButton;
    pointBtn->setText(".");
    connect(pointBtn,SIGNAL(clicked()),this,SLOT(pointClick()));

    QToolButton *mulBtn = new QToolButton;
    mulBtn->setText("*");
    connect(mulBtn,SIGNAL(clicked()),this,SLOT(operatClick()));

    QToolButton *divBtn = new QToolButton;
    divBtn->setText("/");
    connect(divBtn,SIGNAL(clicked()),this,SLOT(operatClick()));

    QToolButton *addBtn = new QToolButton;
    addBtn->setText("+");
    connect(addBtn,SIGNAL(clicked()),this,SLOT(operatClick()));

    QToolButton *subBtn = new QToolButton;
    subBtn->setText("-");
    connect(subBtn,SIGNAL(clicked()),this,SLOT(operatClick()));

    QToolButton *sqrtBtn = new QToolButton;
    sqrtBtn->setText("sqrt");
    connect(sqrtBtn,SIGNAL(clicked()),this,SLOT(unarryClick()));

    QToolButton *powBtn = new QToolButton;
    powBtn->setText("x2");
    connect(powBtn,SIGNAL(clicked()),this,SLOT(unarryClick()));

    QToolButton *countdownBtn = new QToolButton;
    countdownBtn->setText("1/x");
    connect(countdownBtn,SIGNAL(clicked()),this,SLOT(unarryClick()));

    QToolButton *equalBtn = new QToolButton;
    equalBtn->setText("=");
    connect(equalBtn,SIGNAL(clicked()),this,SLOT(operatClick()));

    QToolButton *backspaceBtn = new QToolButton;
    backspaceBtn->setText("Backspace");
    connect(backspaceBtn,SIGNAL(clicked()),this,SLOT(backspaceCk()));

    QToolButton *clearBtn = new QToolButton;
    clearBtn->setText("CE");
    connect(clearBtn,SIGNAL(clicked()),this,SLOT(clear()));

    QToolButton *clearAllBtn = new QToolButton;
    clearAllBtn->setText("C");
    connect(clearAllBtn,SIGNAL(clicked()),this,SLOT(clearAll()));

    QLabel *label = new QLabel;

    QGridLayout *calcu = new QGridLayout;
    for (int i = 0;i < 10; ++i)
    {
        if (i == 0)
            calcu->addWidget(digitButton,3,0);
        else
            calcu->addWidget(digitButton,(9 - i) / 3,i % 3 ? i % 3 - 1 : 2);
    }
    calcu->addWidget(changeBtn,3,1);
    calcu->addWidget(pointBtn,3,2);
    calcu->addWidget(divBtn,0,3);
    calcu->addWidget(mulBtn,1,3);
    calcu->addWidget(subBtn,2,3);
    calcu->addWidget(addBtn,3,3);
    calcu->addWidget(sqrtBtn,0,4);
    calcu->addWidget(powBtn,1,4);
    calcu->addWidget(countdownBtn,2,4);
    calcu->addWidget(equalBtn,3,4);

    QVBoxLayout *memoryLayout = new QVBoxLayout;
    memoryLayout->addWidget(clearMemoryBtn);
    memoryLayout->addWidget(readMemoryBtn);
    memoryLayout->addWidget(setMemoryBtn);
    memoryLayout->addWidget(addMemoryBtn);

    QHBoxLayout *cLayout = new QHBoxLayout;
    cLayout->addLayout(memoryLayout);
    cLayout->addLayout(calcu);

    QGridLayout *upLayout = new QGridLayout;
    upLayout->addWidget(display,0,0,1,4);
    upLayout->addWidget(label,0,1);
    upLayout->addWidget(backspaceBtn,1,1);
    upLayout->addWidget(clearBtn,1,2);
    upLayout->addWidget(clearAllBtn,1,3);

    QVBoxLayout *mainLayout = new QVBoxLayout;
    mainLayout->addLayout(upLayout);
    mainLayout->addLayout(cLayout);
    setLayout(mainLayout);

    setWindowTitle("calculator");
}

void calc::digitClick()
{
    QToolButton *clickedButton = qobject_cast<QToolButton *>(sender());
    int digit = clickedButton->text().toInt();
    if (display->text() == "0" && digit == 0)
        return;
    if (display->text() == "0")
        display->setText("");
    if (waitingForOperand == false)
    {
        display->clear();
        waitingForOperand = true;
    }
    display->setText(display->text() + QString::number(digit));
}

void calc::operatClick()
{
   if (waitingForOperand == false)
       return;
   QToolButton *clickedButton = qobject_cast<QToolButton *>(sender());
   sum = display->text().toDouble();
   ch = clickedButton->text();
   display->setText(display->text());
   waitingForOperand = false;
}

void calc::equalClick() //处理等于按钮
{
    if (ch == "")
        return;
    right = display->text().toDouble();
    if (ch == "+")
        sum += right;
    else if (ch == "-")
        sum -= right;
    else if (ch == "*")
        sum *= right;
    else if (ch == "/")
    {
        if (right == 0)
        {
            wrong();
            return;
        }
        sum /= right;

    }
    display->setText(QString::number(sum));
    ch = "";
    waitingForOperand = true;
}

void calc::changesignClick()
{
    if (waitingForOperand == false)
    {
        ch = "";
        waitingForOperand = true;
    }
    double digit = display->text().toDouble();
    digit = -digit;
    display->setText(QString::number(digit));
}

void calc::pointClick()
{
    if (waitingForOperand == false)
    {
        sum = display->text().toDouble();
        display->setText("0");
    }
    if (!display->text().contains("."))
        display->setText(display->text() + tr("."));
}

void calc::backspaceCk()
{
    if (waitingForOperand == false)
        return;
    QString text = display->text();
    text.chop(1);
    if (text.isEmpty())
        text = '0';
    display->setText(text);
}

void calc::clearAll()
{
    sum = 0.0;
    memory = 0.0;
    right = 0.0;
    ch = "";
    waitingForOperand = true;
    display->setText("0");
}

void calc::clear()
{
    if (waitingForOperand == false)
        return;
    display->setText("0");
}

void calc::clearMemory()
{
    memory = 0.0;
}

void calc::readMemory()
{
    display->setText(QString::number(memory));
}

void calc::setMemory()
{
    memory = display->text().toDouble();
}

void calc::addToMemory()
{
    double temp = display->text().toDouble();
    memory += temp;
}

void calc::unarryClick()
{
    QToolButton *clickedButton = qobject_cast<QToolButton *>(sender());
    QString str = clickedButton->text();
    sum = display->text().toDouble();
    if (str == "sqrt")
        sum = sqrt(sum);
    else if (str == "x2")
        sum *= sum;
    else if (str == "1/x")
        sum = 1.0 / sum;
    display->setText(QString::number(sum));
}

void calc::wrong()
{
    display->setText("error");
}

calc::~calc()
{

}