diff --git a/C_Lab_2/.gitignore b/C_Lab_2/.gitignore
new file mode 100644
index 0000000000000000000000000000000000000000..fab7372d796ea95c80d02df6caa7eb2b411a7ac1
--- /dev/null
+++ b/C_Lab_2/.gitignore
@@ -0,0 +1,73 @@
+# This file is used to ignore files which are generated
+# ----------------------------------------------------------------------------
+
+*~
+*.autosave
+*.a
+*.core
+*.moc
+*.o
+*.obj
+*.orig
+*.rej
+*.so
+*.so.*
+*_pch.h.cpp
+*_resource.rc
+*.qm
+.#*
+*.*#
+core
+!core/
+tags
+.DS_Store
+.directory
+*.debug
+Makefile*
+*.prl
+*.app
+moc_*.cpp
+ui_*.h
+qrc_*.cpp
+Thumbs.db
+*.res
+*.rc
+/.qmake.cache
+/.qmake.stash
+
+# qtcreator generated files
+*.pro.user*
+
+# xemacs temporary files
+*.flc
+
+# Vim temporary files
+.*.swp
+
+# Visual Studio generated files
+*.ib_pdb_index
+*.idb
+*.ilk
+*.pdb
+*.sln
+*.suo
+*.vcproj
+*vcproj.*.*.user
+*.ncb
+*.sdf
+*.opensdf
+*.vcxproj
+*vcxproj.*
+
+# MinGW generated files
+*.Debug
+*.Release
+
+# Python byte code
+*.pyc
+
+# Binaries
+# --------
+*.dll
+*.exe
+
diff --git a/C_Lab_2/C_Lab_2.pro b/C_Lab_2/C_Lab_2.pro
new file mode 100644
index 0000000000000000000000000000000000000000..a9bfcf69417ad8b8f1ffa39e77ea2874a7c083db
--- /dev/null
+++ b/C_Lab_2/C_Lab_2.pro
@@ -0,0 +1,24 @@
+QT += core gui
+QT -=gui
+
+greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
+
+CONFIG += c++11
+
+# You can make your code fail to compile if it uses deprecated APIs.
+# In order to do so, uncomment the following line.
+#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0
+
+SOURCES += \
+    main.cpp \
+    mainwindow.cpp
+
+HEADERS += \
+    mainwindow.h
+
+# Default rules for deployment.
+qnx: target.path = /tmp/$${TARGET}/bin
+else: unix:!android: target.path = /opt/$${TARGET}/bin
+!isEmpty(target.path): INSTALLS += target
+
+FORMS +=
diff --git a/C_Lab_2/main.cpp b/C_Lab_2/main.cpp
index fd3e533415011b7a24814fe7f3ac990d6a811132..55caac816e8a80887e3619c9a3510ce5b696d934 100644
--- a/C_Lab_2/main.cpp
+++ b/C_Lab_2/main.cpp
@@ -5,7 +5,7 @@
 int main(int argc, char *argv[])
 {
     QApplication a(argc, argv);
-    MainWindow w;
+    Calculator w;
     w.show();
     return a.exec();
 }
diff --git a/C_Lab_2/mainwindow.cpp b/C_Lab_2/mainwindow.cpp
index 47b43a3bc7398e068eb05ebfb627df4396b15b9f..752aa65987338a01b2eb9eb7f9e6b33625936f1b 100644
--- a/C_Lab_2/mainwindow.cpp
+++ b/C_Lab_2/mainwindow.cpp
@@ -1,11 +1,319 @@
 #include "mainwindow.h"
+#include <QtGui>
+#include <math.h>
 
-MainWindow::MainWindow(QWidget *parent)
-    : QMainWindow(parent)
+
+Calculator::Calculator(QWidget *parent)
+     : QMainWindow(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;
 }
 
-MainWindow::~MainWindow()
+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;
+}
+
+Button::Button(const QString &text, QWidget *parent)
+     : QToolButton(parent)
+ {
+     setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Preferred);
+     setText(text);
+ }
+
+QSize Button::sizeHint() const
+ {
+     QSize size = QToolButton::sizeHint();
+     size.rheight() += 20;
+     size.rwidth() = qMax(size.width(), size.height());
+     return size;
+ }
diff --git a/C_Lab_2/mainwindow.h b/C_Lab_2/mainwindow.h
index d1471908c8753c630a22fd5b22588cc790cdf28d..c11958c7cf5ebf7e192f6a090217ca586e246f33 100644
--- a/C_Lab_2/mainwindow.h
+++ b/C_Lab_2/mainwindow.h
@@ -2,13 +2,55 @@
 #define MAINWINDOW_H
 
 #include <QMainWindow>
+#include <QToolButton>
+#include <QLineEdit>
+#include <QGridLayout>
 
-class MainWindow : public QMainWindow
+class Button : public QToolButton
 {
     Q_OBJECT
 
 public:
-    MainWindow(QWidget *parent = nullptr);
-    ~MainWindow();
+    Button(const QString &text, QWidget *parent = 0);
+
+    QSize sizeHint() const;
+};
+
+class Calculator : public QMainWindow
+ {
+     Q_OBJECT
+
+ public:
+     Calculator(QWidget *parent = 0);
+
+ private slots:
+     void digitClicked();
+     void unaryOperatorClicked();
+     void additiveOperatorClicked();
+     void multiplicativeOperatorClicked();
+     void equalClicked();
+     void pointClicked();
+     void changeSignClicked();
+     void backspaceClicked();
+     void clear();
+     void clearAll();
+     void clearMemory();
+     void readMemory();
+     void setMemory();
+     void addToMemory();
+private:
+     Button *createButton(const QString &text, const char *member);
+     void abortOperation();
+     bool calculate(double rightOperand, const QString &pendingOperator);
+     double sumInMemory;
+     double sumSoFar;
+     double factorSoFar;
+     QString pendingAdditiveOperator;
+     QString pendingMultiplicativeOperator;
+     bool waitingForOperand;
+     QLineEdit *display;
+     enum { NumDigitButtons = 10 };
+     Button *digitButtons[NumDigitButtons];
 };
+
 #endif // MAINWINDOW_H
diff --git a/C_Lab_2/mainwindow.ui b/C_Lab_2/mainwindow.ui
new file mode 100644
index 0000000000000000000000000000000000000000..b637ad661edc6583ef6b9f2dc4197fe149c80203
--- /dev/null
+++ b/C_Lab_2/mainwindow.ui
@@ -0,0 +1,25 @@
+<ui version="4.0" >
+ <author></author>
+ <comment></comment>
+ <exportmacro></exportmacro>
+ <class>MainWindow</class>
+ <widget class="QMainWindow" name="MainWindow" >
+  <property name="geometry" >
+   <rect>
+    <x>0</x>
+    <y>0</y>
+    <width>800</width>
+    <height>600</height>
+   </rect>
+  </property>
+  <property name="windowTitle" >
+   <string>MainWindow</string>
+  </property>
+  <widget class="QMenuBar" name="menubar" />
+  <widget class="QWidget" name="centralwidget" />
+  <widget class="QStatusBar" name="statusbar" />
+ </widget>
+ <pixmapfunction></pixmapfunction>
+ <connections/>
+</ui>
+