diff --git a/kcm/src/declarative/qmloutput.cpp b/kcm/src/declarative/qmloutput.cpp
--- a/kcm/src/declarative/qmloutput.cpp
+++ b/kcm/src/declarative/qmloutput.cpp
@@ -114,7 +114,7 @@
 
 void QMLOutput::undockLeft()
 {
-    setLeftDockedTo(0);
+    setLeftDockedTo(nullptr);
 }
 
 void QMLOutput::setTopDockedTo(QMLOutput *output)
@@ -134,7 +134,7 @@
 
 void QMLOutput::undockTop()
 {
-    setTopDockedTo(0);
+    setTopDockedTo(nullptr);
 }
 
 void QMLOutput::setRightDockedTo(QMLOutput *output)
@@ -154,7 +154,7 @@
 
 void QMLOutput::undockRight()
 {
-    setRightDockedTo(0);
+    setRightDockedTo(nullptr);
 }
 
 void QMLOutput::setBottomDockedTo(QMLOutput *output)
@@ -174,7 +174,7 @@
 
 void QMLOutput::undockBottom()
 {
-    setBottomDockedTo(0);
+    setBottomDockedTo(nullptr);
 }
 
 void QMLOutput::setCloneOf(QMLOutput* other)
@@ -536,7 +536,7 @@
     const QList<QQuickItem*> siblings = screen()->childItems();
 
     // First, if we have moved, then unset the "cloneOf" flag
-    setCloneOf(0);
+    setCloneOf(nullptr);
 
     disconnect(this, &QMLOutput::xChanged, this, static_cast<void(QMLOutput::*)()>(&QMLOutput::moved));
     disconnect(this, &QMLOutput::yChanged, this, static_cast<void(QMLOutput::*)()>(&QMLOutput::moved));
diff --git a/kcm/src/declarative/qmlscreen.cpp b/kcm/src/declarative/qmlscreen.cpp
--- a/kcm/src/declarative/qmlscreen.cpp
+++ b/kcm/src/declarative/qmlscreen.cpp
@@ -58,7 +58,7 @@
 {
     qDeleteAll(m_outputMap);
     m_outputMap.clear();
-    m_bottommost = m_leftmost = m_rightmost = m_topmost = 0;
+    m_bottommost = m_leftmost = m_rightmost = m_topmost = nullptr;
     m_connectedOutputsCount = 0;
     m_enabledOutputsCount = 0;
 
@@ -286,10 +286,10 @@
 
 void QMLScreen::updateCornerOutputs()
 {
-    m_leftmost = 0;
-    m_topmost = 0;
-    m_rightmost = 0;
-    m_bottommost = 0;
+    m_leftmost = nullptr;
+    m_topmost = nullptr;
+    m_rightmost = nullptr;
+    m_bottommost = nullptr;
 
     Q_FOREACH (QMLOutput *output, m_outputMap) {
         if (!output->output()->isConnected() || !output->output()->isEnabled()) {
diff --git a/kcm/src/resolutionslider.cpp b/kcm/src/resolutionslider.cpp
--- a/kcm/src/resolutionslider.cpp
+++ b/kcm/src/resolutionslider.cpp
@@ -79,7 +79,7 @@
         mCurrentLabel->setAlignment(Qt::AlignCenter);
         layout->addWidget(mCurrentLabel, 1, 0, 1, 3);
 
-        if (mModes.count() == 0) {
+        if (mModes.isEmpty()) {
             mCurrentLabel->setText(i18n("No available resolutions"));
         } else if (mModes.count() == 1) {
             mCurrentLabel->setText(Utils::sizeToString(mModes.first()));
diff --git a/kcm/src/unifiedoutputconfig.cpp b/kcm/src/unifiedoutputconfig.cpp
--- a/kcm/src/unifiedoutputconfig.cpp
+++ b/kcm/src/unifiedoutputconfig.cpp
@@ -66,6 +66,7 @@
     mOutput = output;
 
     mClones.clear();
+    mClones.reserve(mOutput->clones().count());
     Q_FOREACH (int id, mOutput->clones()) {
         mClones << mConfig->output(id);
     }
diff --git a/kcm/src/widget.cpp b/kcm/src/widget.cpp
--- a/kcm/src/widget.cpp
+++ b/kcm/src/widget.cpp
@@ -78,7 +78,7 @@
     widget->setSizePolicy(QSizePolicy::Preferred, QSizePolicy::MinimumExpanding);
 
     QVBoxLayout *vbox = new QVBoxLayout(widget);
-    const int topMargin = style()->pixelMetric(QStyle::PM_LayoutTopMargin, 0, this);
+    const int topMargin = style()->pixelMetric(QStyle::PM_LayoutTopMargin, nullptr, this);
     vbox->setContentsMargins(0, topMargin, 0, 0);
     widget->setLayout(vbox);
 
@@ -291,7 +291,7 @@
                 continue;
             }
 
-            if (base == 0) {
+            if (!base) {
                 base = output;
             }
 
diff --git a/kded/generator.cpp b/kded/generator.cpp
--- a/kded/generator.cpp
+++ b/kded/generator.cpp
@@ -569,8 +569,8 @@
 
 KScreen::ModePtr Generator::bestModeForOutput(const KScreen::OutputPtr &output)
 {
-    if (output->preferredMode()) {
-        return output->preferredMode();
+    if (KScreen::ModePtr outputMode = output->preferredMode()) {
+        return outputMode;
     }
 
     return biggestMode(output->modes());
diff --git a/kded/osd.h b/kded/osd.h
--- a/kded/osd.h
+++ b/kded/osd.h
@@ -41,7 +41,7 @@
     Q_OBJECT
 
 public:
-    Osd(const KScreen::OutputPtr output, QObject *parent = nullptr);
+    Osd(const OutputPtr &output, QObject *parent = nullptr);
     ~Osd() override;
 
     void showGenericOsd(const QString &icon, const QString &text);
diff --git a/kded/osd.cpp b/kded/osd.cpp
--- a/kded/osd.cpp
+++ b/kded/osd.cpp
@@ -31,7 +31,7 @@
 
 using namespace KScreen;
 
-Osd::Osd(const KScreen::OutputPtr output, QObject *parent)
+Osd::Osd(const KScreen::OutputPtr &output, QObject *parent)
     : QObject(parent)
     , m_output(output)
 {