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# calculator.cpp Example File
widgets/calculator/calculator.cpp

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     #include <QtGui>

     #include <math.h>

     #include "button.h"
     #include "calculator.h"

     Calculator::Calculator(QWidget *parent)
         : QDialog(parent)
     {
         sumInMemory = 0.0;
         sumSoFar = 0.0;
         factorSoFar = 0.0;
         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 < NumDigitButtons; ++i) {
             digitButtons[i] = createButton(QString::number(i), SLOT(digitClicked()));
         }

         Button *pointButton = createButton(tr("."), SLOT(pointClicked()));
         Button *changeSignButton = createButton(tr("\261"), SLOT(changeSignClicked()));

         Button *backspaceButton = createButton(tr("Backspace"), SLOT(backspaceClicked()));
         Button *clearButton = createButton(tr("Clear"), SLOT(clear()));
         Button *clearAllButton = createButton(tr("Clear All"), SLOT(clearAll()));

         Button *clearMemoryButton = createButton(tr("MC"), SLOT(clearMemory()));
         Button *readMemoryButton = createButton(tr("MR"), SLOT(readMemory()));
         Button *setMemoryButton = createButton(tr("MS"), SLOT(setMemory()));
         Button *addToMemoryButton = createButton(tr("M+"), SLOT(addToMemory()));

         Button *divisionButton = createButton(tr("\367"), SLOT(multiplicativeOperatorClicked()));
         Button *timesButton = createButton(tr("\327"), SLOT(multiplicativeOperatorClicked()));
         Button *minusButton = createButton(tr("-"), SLOT(additiveOperatorClicked()));
         Button *plusButton = createButton(tr("+"), SLOT(additiveOperatorClicked()));

         Button *squareRootButton = createButton(tr("Sqrt"), SLOT(unaryOperatorClicked()));
         Button *powerButton = createButton(tr("x\262"), SLOT(unaryOperatorClicked()));
         Button *reciprocalButton = createButton(tr("1/x"), SLOT(unaryOperatorClicked()));
         Button *equalButton = createButton(tr("="), SLOT(equalClicked()));

         QGridLayout *mainLayout = new QGridLayout;
         mainLayout->setSizeConstraint(QLayout::SetFixedSize);

         mainLayout->addWidget(display, 0, 0, 1, 6);
         mainLayout->addWidget(backspaceButton, 1, 0, 1, 2);
         mainLayout->addWidget(clearButton, 1, 2, 1, 2);
         mainLayout->addWidget(clearAllButton, 1, 4, 1, 2);

         mainLayout->addWidget(clearMemoryButton, 2, 0);
         mainLayout->addWidget(readMemoryButton, 3, 0);
         mainLayout->addWidget(setMemoryButton, 4, 0);
         mainLayout->addWidget(addToMemoryButton, 5, 0);

         for (int i = 1; i < NumDigitButtons; ++i) {
             int row = ((9 - i) / 3) + 2;
             int column = ((i - 1) % 3) + 1;
             mainLayout->addWidget(digitButtons[i], row, column);
         }

         mainLayout->addWidget(digitButtons[0], 5, 1);
         mainLayout->addWidget(pointButton, 5, 2);
         mainLayout->addWidget(changeSignButton, 5, 3);

         mainLayout->addWidget(divisionButton, 2, 4);
         mainLayout->addWidget(timesButton, 3, 4);
         mainLayout->addWidget(minusButton, 4, 4);
         mainLayout->addWidget(plusButton, 5, 4);

         mainLayout->addWidget(squareRootButton, 2, 5);
         mainLayout->addWidget(powerButton, 3, 5);
         mainLayout->addWidget(reciprocalButton, 4, 5);
         mainLayout->addWidget(equalButton, 5, 5);
         setLayout(mainLayout);

         setWindowTitle(tr("Calculator"));
     }

     void Calculator::digitClicked()
     {
         Button *clickedButton = qobject_cast<Button *>(sender());
         int digitValue = clickedButton->text().toInt();
         if (display->text() == "0" && digitValue == 0.0)
             return;

         if (waitingForOperand) {
             display->clear();
             waitingForOperand = false;
         }
         display->setText(display->text() + QString::number(digitValue));
     }

     void Calculator::unaryOperatorClicked()
     {
         Button *clickedButton = qobject_cast<Button *>(sender());
         QString clickedOperator = clickedButton->text();
         double operand = display->text().toDouble();
         double result = 0.0;

         if (clickedOperator == tr("Sqrt")) {
             if (operand < 0.0) {
                 abortOperation();
                 return;
             }
             result = sqrt(operand);
         } else if (clickedOperator == tr("x\262")) {
             result = pow(operand, 2.0);
         } else if (clickedOperator == tr("1/x")) {
             if (operand == 0.0) {
                 abortOperation();
                 return;
             }
             result = 1.0 / operand;
         }
         display->setText(QString::number(result));
         waitingForOperand = true;
     }

     void Calculator::additiveOperatorClicked()
     {
         Button *clickedButton = qobject_cast<Button *>(sender());
         QString clickedOperator = clickedButton->text();
         double operand = display->text().toDouble();

         if (!pendingMultiplicativeOperator.isEmpty()) {
             if (!calculate(operand, pendingMultiplicativeOperator)) {
                 abortOperation();
                 return;
             }
             display->setText(QString::number(factorSoFar));
             operand = factorSoFar;
             factorSoFar = 0.0;
             pendingMultiplicativeOperator.clear();
         }

         if (!pendingAdditiveOperator.isEmpty()) {
             if (!calculate(operand, pendingAdditiveOperator)) {
                 abortOperation();
                 return;
             }
             display->setText(QString::number(sumSoFar));
         } else {
             sumSoFar = operand;
         }

         pendingAdditiveOperator = clickedOperator;
         waitingForOperand = true;
     }

     void Calculator::multiplicativeOperatorClicked()
     {
         Button *clickedButton = qobject_cast<Button *>(sender());
         QString clickedOperator = clickedButton->text();
         double operand = display->text().toDouble();

         if (!pendingMultiplicativeOperator.isEmpty()) {
             if (!calculate(operand, pendingMultiplicativeOperator)) {
                 abortOperation();
                 return;
             }
             display->setText(QString::number(factorSoFar));
         } else {
             factorSoFar = operand;
         }

         pendingMultiplicativeOperator = clickedOperator;
         waitingForOperand = true;
     }

     void Calculator::equalClicked()
     {
         double operand = display->text().toDouble();

         if (!pendingMultiplicativeOperator.isEmpty()) {
             if (!calculate(operand, pendingMultiplicativeOperator)) {
                 abortOperation();
                 return;
             }
             operand = factorSoFar;
             factorSoFar = 0.0;
             pendingMultiplicativeOperator.clear();
         }
         if (!pendingAdditiveOperator.isEmpty()) {
             if (!calculate(operand, pendingAdditiveOperator)) {
                 abortOperation();
                 return;
             }
             pendingAdditiveOperator.clear();
         } else {
             sumSoFar = operand;
         }

         display->setText(QString::number(sumSoFar));
         sumSoFar = 0.0;
         waitingForOperand = true;
     }

     void Calculator::pointClicked()
     {
         if (waitingForOperand)
             display->setText("0");
         if (!display->text().contains("."))
             display->setText(display->text() + tr("."));
         waitingForOperand = false;
     }

     void Calculator::changeSignClicked()
     {
         QString text = display->text();
         double value = text.toDouble();

         if (value > 0.0) {
             text.prepend(tr("-"));
         } else if (value < 0.0) {
             text.remove(0, 1);
         }
         display->setText(text);
     }

     void Calculator::backspaceClicked()
     {
         if (waitingForOperand)
             return;

         QString text = display->text();
         text.chop(1);
         if (text.isEmpty()) {
             text = "0";
             waitingForOperand = true;
         }
         display->setText(text);
     }

     void Calculator::clear()
     {
         if (waitingForOperand)
             return;

         display->setText("0");
         waitingForOperand = true;
     }

     void Calculator::clearAll()
     {
         sumSoFar = 0.0;
         factorSoFar = 0.0;
         pendingAdditiveOperator.clear();
         pendingMultiplicativeOperator.clear();
         display->setText("0");
         waitingForOperand = true;
     }

     void Calculator::clearMemory()
     {
         sumInMemory = 0.0;
     }

     void Calculator::readMemory()
     {
         display->setText(QString::number(sumInMemory));
         waitingForOperand = true;
     }

     void Calculator::setMemory()
     {
         equalClicked();
         sumInMemory = display->text().toDouble();
     }

     void Calculator::addToMemory()
     {
         equalClicked();
         sumInMemory += display->text().toDouble();
     }
     Button *Calculator::createButton(const QString &text, const char *member)
     {
         Button *button = new Button(text);
         connect(button, SIGNAL(clicked()), this, member);
         return button;
     }

     void Calculator::abortOperation()
     {
         clearAll();
         display->setText(tr("####"));
     }

     bool Calculator::calculate(double rightOperand, const QString &pendingOperator)
     {
         if (pendingOperator == tr("+")) {
             sumSoFar += rightOperand;
         } else if (pendingOperator == tr("-")) {
             sumSoFar -= rightOperand;
         } else if (pendingOperator == tr("\327")) {
             factorSoFar *= rightOperand;
         } else if (pendingOperator == tr("\367")) {
             if (rightOperand == 0.0)
                 return false;
             factorSoFar /= rightOperand;
         }
         return true;
     }