diff --git a/main.cpp b/main.cpp
index aab39bb8988f6eeeb6f19b8feeebc0f03e8a969b..3cf5e903e850b977939e79d0dc5c5d0f39037f53 100644
--- a/main.cpp
+++ b/main.cpp
@@ -7,5 +7,5 @@ int main(int argc, char *argv[])
     MainWindow w;
     w.show();
 
-    return a.exec();
+    return QApplication::exec();
 }
diff --git a/mainwindow.cpp b/mainwindow.cpp
index 33372b310d5f0a1dd291d08c9ef58498413cf12b..69a1212a79a48dee0baea5a2bc1fcfddd81df604 100644
--- a/mainwindow.cpp
+++ b/mainwindow.cpp
@@ -3,19 +3,19 @@
 #include <QFileDialog>
 #include <QInputDialog>
 
-static auto FILTERS = QStringList() << "*.cpp" << "*.cc" << "*.cxx" << "*.c++" << "*.c" << "*.tpp"
-                                    << "*.hpp" << "*.hh" << "*.hxx" << "*.h++" << "*.h" << "*.cl";
+namespace  {
+QStringList& FILTERS();
+QStringList subDirs(const QDir& dir);
+} // unnamed namespace
 
-static QStringList subDirs(const QDir &dir);
-
-MainWindow::MainWindow(QWidget *parent) :
+MainWindow::MainWindow(QWidget* parent) :
     QMainWindow(parent),
     ui(new Ui::MainWindow)
 {
     ui->setupUi(this);
-    connect(ui->checkBox_subFolders,&QCheckBox::toggled,this,&MainWindow::updateFolderList);
-    connect(ui->checkBox_emptyLines,&QCheckBox::toggled,this,&MainWindow::updateFolderList);
-    connect(this,&MainWindow::updateFolderList,this,&MainWindow::lines);
+    connect(ui->checkBox_subFolders, &QCheckBox::toggled, this, &MainWindow::updateFolderList);
+    connect(ui->checkBox_emptyLines, &QCheckBox::toggled, this, &MainWindow::updateFolderList);
+    connect(this, &MainWindow::updateFolderList, this, &MainWindow::lines);
 }
 
 MainWindow::~MainWindow()
@@ -25,8 +25,9 @@ MainWindow::~MainWindow()
 
 void MainWindow::on_pushButton_addFolder_clicked()
 {
-    auto name = QFileDialog::getExistingDirectory(this,"Select a folder to add");
-    if(!name.isEmpty()) ui->textBrowser->append(name);
+    auto name = QFileDialog::getExistingDirectory(this, "Select a folder to add");
+    if(!name.isEmpty())
+        ui->textBrowser->append(name);
     emit updateFolderList();
 }
 
@@ -58,23 +59,23 @@ void MainWindow::on_pushButton_addExtension_clicked()
     auto text = QInputDialog::getText(this, "Insert file extension",
                                "*.", QLineEdit::Normal, "txt", &ok);
     if(ok) {
-        FILTERS << "*."+text;
+        FILTERS() << "*." + text;
         emit updateFolderList();
     }
 }
 
 void MainWindow::on_pushButton_removeFirstExtension_clicked()
 {
-    if(!FILTERS.isEmpty()) {
-        FILTERS.removeFirst();
+    if(!FILTERS().isEmpty()) {
+        FILTERS().removeFirst();
         emit updateFolderList();
     }
 }
 
 void MainWindow::on_pushButton_removeLastExtension_clicked()
 {
-    if(!FILTERS.isEmpty()) {
-        FILTERS.removeLast();
+    if(!FILTERS().isEmpty()) {
+        FILTERS().removeLast();
         emit updateFolderList();
     }
 }
@@ -90,7 +91,7 @@ void MainWindow::lines()
     if(ui->checkBox_subFolders->isChecked())
     {
         QStringList subs;
-        for(const auto& f : folderList)
+        for(const auto& f : qAsConst(folderList))
             subs.append(subDirs(f));
         folderList.append(subs);
     }
@@ -98,19 +99,6 @@ void MainWindow::lines()
     countLines(folderList);
 }
 
-QStringList subDirs(const QDir &dir)
-{
-    QStringList ret;
-    auto subs = dir.entryList(QDir::Dirs);
-    subs.removeOne(".");
-    subs.removeOne("..");
-    for(auto &s : subs)
-        s = dir.absolutePath()+"/"+s;
-    for(const auto &s : subs)
-        ret.append(subDirs(s));
-    return subs + ret;
-}
-
 QStringList MainWindow::folders()
 {
     auto content = ui->textBrowser->toPlainText();
@@ -121,26 +109,27 @@ void MainWindow::countLines(const QStringList &folders)
 {
     QString analysis("$$$$$ ANALYSIS $$$$$\n\n"
                      "located folders:\n" + folders.join("\n") + "\n\n" +
-                     "located files with extensions\n" + FILTERS.join(", ") + ":\n\n");
+                     "located files with extensions\n" + FILTERS().join(", ") + ":\n\n");
     QFile curFile;
     auto lineCounter = 0;
     auto fileCounter = 0;
 
-    if(!FILTERS.isEmpty()) {
-        for(QDir curDir : folders)
+    if(!FILTERS().isEmpty()) {
+        for(const QDir curDir : folders)
         {
-            auto fileList = curDir.entryList(FILTERS);
+            auto fileList = curDir.entryList(FILTERS());
             fileCounter += fileList.length();
-            for(const auto &fileN : fileList)
+            for(const auto& fileN : qAsConst(fileList))
             {
-                curFile.setFileName(curDir.path()+"/" +fileN);
+                curFile.setFileName(curDir.path() + QStringLiteral("/") + fileN);
                 curFile.open(QIODevice::ReadOnly | QIODevice::Text);
                 auto allLines = QString(curFile.readAll());
-                auto listOfLines = allLines.split("\n");
+                auto listOfLines = allLines.split(QStringLiteral("\n"));
                 if(!ui->checkBox_emptyLines->isChecked())
                     listOfLines.removeAll("");
                 auto curLength = listOfLines.length();
-                analysis.append(fileN + ":  " + QString::number(curLength) + "\n");
+                analysis.append(fileN + QStringLiteral(":  ") + QString::number(curLength) +
+                                QStringLiteral("\n"));
                 lineCounter += curLength;
                 curFile.close();
             }
@@ -150,3 +139,27 @@ void MainWindow::countLines(const QStringList &folders)
     ui->textBrowser_analysis->setText(analysis);
     ui->label_number->setText(QString::number(lineCounter));
 }
+
+namespace  {
+
+QStringList& FILTERS()
+{
+    static auto ret{ QStringList() << "*.cpp" << "*.cc" << "*.cxx" << "*.c++" << "*.c" << "*.tpp"
+                                   << "*.hpp" << "*.hh" << "*.hxx" << "*.h++" << "*.h" << "*.cl" };
+    return ret;
+}
+
+QStringList subDirs(const QDir& dir)
+{
+    QStringList ret;
+    auto subs = dir.entryList(QDir::Dirs);
+    subs.removeOne(QStringLiteral("."));
+    subs.removeOne(QStringLiteral(".."));
+    for(auto& s : subs)
+        s = dir.absolutePath() + QStringLiteral("/") +s;
+    for(const auto& s : subs)
+        ret.append(subDirs(s));
+    return subs + ret;
+}
+
+} // unnamed namespace
diff --git a/mainwindow.h b/mainwindow.h
index 1c8a37b265fb2a3b9accaf341dc586003a7095e2..78d4c69c9acd932980b94a69d0ce28acea5d8613 100644
--- a/mainwindow.h
+++ b/mainwindow.h
@@ -12,7 +12,7 @@ class MainWindow : public QMainWindow
     Q_OBJECT
 
 public:
-    explicit MainWindow(QWidget *parent = 0);
+    explicit MainWindow(QWidget* parent = nullptr);
     ~MainWindow();
 
 private slots:
@@ -26,11 +26,12 @@ private slots:
 
 signals:
     void updateFolderList();
+
 private:
     void lines();
-    void countLines(const QStringList &folders);
+    void countLines(const QStringList& folders);
     QStringList folders();
-    Ui::MainWindow *ui;
+    Ui::MainWindow* ui;
 };
 
 #endif // MAINWINDOW_H