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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);

     QColor digitColor(150, 205, 205);
     QColor backspaceColor(225, 185, 135);
     QColor memoryColor(100, 155, 155);
     QColor operatorColor(155, 175, 195);

     for (int i = 0; i < NumDigitButtons; ++i) {
         digitButtons[i] = createButton(QString::number(i), digitColor,
                                        SLOT(digitClicked()));
     }

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

     Button *backspaceButton = createButton(tr("Backspace"), backspaceColor,
                                    SLOT(backspaceClicked()));
     Button *clearButton = createButton(tr("Clear"), backspaceColor, SLOT(clear()));
     Button *clearAllButton = createButton(tr("Clear All"), backspaceColor.light(120),
                                   SLOT(clearAll()));

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

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

     Button *squareRootButton = createButton(tr("Sqrt"), operatorColor,
                                     SLOT(unaryOperatorClicked()));
     Button *powerButton = createButton(tr("x\262"), operatorColor,
                                SLOT(unaryOperatorClicked()));
     Button *reciprocalButton = createButton(tr("1/x"), operatorColor,
                                     SLOT(unaryOperatorClicked()));
     Button *equalButton = createButton(tr("="), operatorColor.light(120),
                                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 QColor &color,
                                  const char *member)
 {
     Button *button = new Button(text, color);
     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;
 }