diff --git a/autotests/drm/mock_drm.h b/autotests/drm/mock_drm.h
index ae80769777..bba6edfa32 100644
--- a/autotests/drm/mock_drm.h
+++ b/autotests/drm/mock_drm.h
@@ -18,8 +18,8 @@ You should have received a copy of the GNU General Public License
 along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *********************************************************************/
 #pragma once
-#include <stddef.h>
-#include <stdint.h>
+#include <cstddef>
+#include <cstdint>
 #include <xf86drmMode.h>
 
 #include <QVector>
diff --git a/autotests/integration/helper/kill.cpp b/autotests/integration/helper/kill.cpp
index 586806d65d..68647dac3b 100644
--- a/autotests/integration/helper/kill.cpp
+++ b/autotests/integration/helper/kill.cpp
@@ -24,7 +24,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include <QWidget>
 #include <unistd.h>
 
-#include <signal.h>
+#include <csignal>
 
 int main(int argc, char *argv[])
 {
diff --git a/autotests/integration/shell_client_test.cpp b/autotests/integration/shell_client_test.cpp
index 5a10cda006..fd503764ac 100644
--- a/autotests/integration/shell_client_test.cpp
+++ b/autotests/integration/shell_client_test.cpp
@@ -55,7 +55,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include <sys/types.h>
 #include <sys/socket.h>
 #include <unistd.h>
-#include <signal.h>
+
+#include <csignal>
 
 using namespace KWin;
 using namespace KWayland::Client;
diff --git a/client.cpp b/client.cpp
index 17799253d1..bd2f0aeba4 100644
--- a/client.cpp
+++ b/client.cpp
@@ -59,7 +59,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include <xcb/xcb_icccm.h>
 // system
 #include <unistd.h>
-#include <signal.h>
+// c++
+#include <csignal>
 
 // Put all externs before the namespace statement to allow the linker
 // to resolve them properly
diff --git a/colorcorrection/suncalc.cpp b/colorcorrection/suncalc.cpp
index 64cc2cfb0c..217d788b6a 100644
--- a/colorcorrection/suncalc.cpp
+++ b/colorcorrection/suncalc.cpp
@@ -21,7 +21,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "constants.h"
 
 #include <QDateTime>
-#include <qmath.h>
+#include <QtMath>
 
 namespace KWin {
 namespace ColorCorrect {
diff --git a/effects.cpp b/effects.cpp
index d269510074..916b71917a 100644
--- a/effects.cpp
+++ b/effects.cpp
@@ -51,7 +51,6 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 #include <Plasma/Theme>
 
-#include <assert.h>
 #include "composite.h"
 #include "xcbutils.h"
 #include "platform.h"
@@ -61,6 +60,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "decorations/decorationbridge.h"
 #include <KDecoration2/DecorationSettings>
 
+#include <cassert>
+
 namespace KWin
 {
 //---------------------
diff --git a/effects/cube/cube.cpp b/effects/cube/cube.cpp
index 986c373046..576a000e3f 100644
--- a/effects/cube/cube.cpp
+++ b/effects/cube/cube.cpp
@@ -39,7 +39,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include <QVector2D>
 #include <QVector3D>
 
-#include <math.h>
+#include <cmath>
 
 #include <kwinglutils.h>
 #include <kwinglplatform.h>
diff --git a/effects/cubeslide/cubeslide.cpp b/effects/cubeslide/cubeslide.cpp
index f4725e2915..d3e86eb19e 100644
--- a/effects/cubeslide/cubeslide.cpp
+++ b/effects/cubeslide/cubeslide.cpp
@@ -23,11 +23,11 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "cubeslideconfig.h"
 
 #include <kwinconfig.h>
-#include <QVector3D>
+#include <kwinglutils.h>
 
-#include <math.h>
+#include <QVector3D>
 
-#include <kwinglutils.h>
+#include <cmath>
 
 namespace KWin
 {
diff --git a/effects/desktopgrid/desktopgrid.cpp b/effects/desktopgrid/desktopgrid.cpp
index 2430544fcd..b162f22dcf 100644
--- a/effects/desktopgrid/desktopgrid.cpp
+++ b/effects/desktopgrid/desktopgrid.cpp
@@ -27,8 +27,6 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "../presentwindows/presentwindows_proxy.h"
 #include "../effect_builtins.h"
 
-#include <math.h>
-
 #include <QAction>
 #include <QApplication>
 #include <KGlobalAccel>
@@ -44,6 +42,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 #include <KWayland/Server/surface_interface.h>
 
+#include <cmath>
+
 namespace KWin
 {
 
diff --git a/effects/fallapart/fallapart.cpp b/effects/fallapart/fallapart.cpp
index 20d44f8d58..73f89d34b4 100644
--- a/effects/fallapart/fallapart.cpp
+++ b/effects/fallapart/fallapart.cpp
@@ -21,8 +21,9 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "fallapart.h"
 // KConfigSkeleton
 #include "fallapartconfig.h"
-#include <assert.h>
-#include <math.h>
+
+#include <cassert>
+#include <cmath>
 
 namespace KWin
 {
diff --git a/effects/mouseclick/mouseclick.cpp b/effects/mouseclick/mouseclick.cpp
index 4cf5788a40..baa53f5913 100644
--- a/effects/mouseclick/mouseclick.cpp
+++ b/effects/mouseclick/mouseclick.cpp
@@ -36,7 +36,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 #include <QPainter>
 
-#include <math.h>
+#include <cmath>
 
 namespace KWin
 {
diff --git a/effects/mousemark/mousemark.cpp b/effects/mousemark/mousemark.cpp
index e969d16bf8..a205ea13c8 100644
--- a/effects/mousemark/mousemark.cpp
+++ b/effects/mousemark/mousemark.cpp
@@ -33,7 +33,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 #include <QPainter>
 
-#include <math.h>
+#include <cmath>
 
 #ifdef KWIN_HAVE_XRENDER_COMPOSITING
 #include <xcb/render.h>
diff --git a/effects/presentwindows/presentwindows.cpp b/effects/presentwindows/presentwindows.cpp
index b37c771e43..31f19e8c0c 100644
--- a/effects/presentwindows/presentwindows.cpp
+++ b/effects/presentwindows/presentwindows.cpp
@@ -31,9 +31,6 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include <QMouseEvent>
 #include <netwm_def.h>
 
-#include <math.h>
-#include <assert.h>
-#include <limits.h>
 #include <QApplication>
 #include <QQmlContext>
 #include <QQmlEngine>
@@ -45,6 +42,10 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include <QVector2D>
 #include <QVector4D>
 
+#include <cassert>
+#include <climits>
+#include <cmath>
+
 namespace KWin
 {
 
diff --git a/effects/showfps/showfps.cpp b/effects/showfps/showfps.cpp
index b17aa2342e..8224565e77 100644
--- a/effects/showfps/showfps.cpp
+++ b/effects/showfps/showfps.cpp
@@ -32,11 +32,13 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #endif
 
 #include <KLocalizedString>
-#include <math.h>
+
 #include <QPainter>
 #include <QVector2D>
 #include <QPalette>
 
+#include <cmath>
+
 namespace KWin
 {
 
diff --git a/effects/thumbnailaside/thumbnailaside.h b/effects/thumbnailaside/thumbnailaside.h
index bfe4931cd5..ac38ea5b2b 100644
--- a/effects/thumbnailaside/thumbnailaside.h
+++ b/effects/thumbnailaside/thumbnailaside.h
@@ -30,7 +30,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 #include <kwineffects.h>
 
-#include <qhash.h>
+#include <QHash>
 
 namespace KWin
 {
diff --git a/effects/touchpoints/touchpoints.cpp b/effects/touchpoints/touchpoints.cpp
index 71a746943a..99063d2744 100644
--- a/effects/touchpoints/touchpoints.cpp
+++ b/effects/touchpoints/touchpoints.cpp
@@ -35,7 +35,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 #include <QPainter>
 
-#include <math.h>
+#include <cmath>
 
 namespace KWin
 {
diff --git a/effects/trackmouse/trackmouse.cpp b/effects/trackmouse/trackmouse.cpp
index 8a2630089f..534b98f240 100644
--- a/effects/trackmouse/trackmouse.cpp
+++ b/effects/trackmouse/trackmouse.cpp
@@ -37,7 +37,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include <KGlobalAccel>
 #include <KLocalizedString>
 
-#include <math.h>
+#include <cmath>
 
 namespace KWin
 {
diff --git a/effects/wobblywindows/wobblywindows.cpp b/effects/wobblywindows/wobblywindows.cpp
index 40f543aef3..6dcaeecf91 100644
--- a/effects/wobblywindows/wobblywindows.cpp
+++ b/effects/wobblywindows/wobblywindows.cpp
@@ -12,7 +12,7 @@ License. See the file "COPYING" for the exact licensing terms.
 #include "wobblywindows.h"
 #include "wobblywindowsconfig.h"
 
-#include <math.h>
+#include <cmath>
 
 //#define COMPUTE_STATS
 
diff --git a/group.cpp b/group.cpp
index 70bb2bfa93..2183ef8551 100644
--- a/group.cpp
+++ b/group.cpp
@@ -33,11 +33,12 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "client.h"
 #include "effects.h"
 
-#include <assert.h>
 #include <kstartupinfo.h>
 #include <KWindowSystem>
 #include <QDebug>
 
+#include <cassert>
+
 
 /*
  TODO
diff --git a/helpers/killer/killer.cpp b/helpers/killer/killer.cpp
index 1dd25ea613..608a91aaf2 100644
--- a/helpers/killer/killer.cpp
+++ b/helpers/killer/killer.cpp
@@ -26,14 +26,15 @@ DEALINGS IN THE SOFTWARE.
 #include <KLocalizedString>
 #include <KAuth/KAuthAction>
 #include <QApplication>
-#include <qcommandlineparser.h>
+#include <QCommandLineParser>
 #include <QDebug>
 #include <QProcess>
 #include <QtX11Extras/QX11Info>
-#include <signal.h>
-#include <errno.h>
 #include <xcb/xcb.h>
 
+#include <cerrno>
+#include <csignal>
+
 int main(int argc, char* argv[])
 {
     KLocalizedString::setApplicationDomain("kwin");
diff --git a/kcmkwin/kwindecoration/declarative-plugin/plugin.cpp b/kcmkwin/kwindecoration/declarative-plugin/plugin.cpp
index 1eb823b52c..54144f5167 100644
--- a/kcmkwin/kwindecoration/declarative-plugin/plugin.cpp
+++ b/kcmkwin/kwindecoration/declarative-plugin/plugin.cpp
@@ -28,8 +28,6 @@
 #include <KDecoration2/Decoration>
 #include <KDecoration2/DecorationShadow>
 
-#include <qqml.h>
-
 namespace KDecoration2
 {
 namespace Preview
diff --git a/kcmkwin/kwinoptions/mouse.cpp b/kcmkwin/kwinoptions/mouse.cpp
index 0d9678c305..fd2ca2b681 100644
--- a/kcmkwin/kwinoptions/mouse.cpp
+++ b/kcmkwin/kwinoptions/mouse.cpp
@@ -43,7 +43,7 @@
 #include <X11/Xlib.h>
 #include <X11/Xutil.h>
 
-#include <stdlib.h>
+#include <cstdlib>
 
 
 namespace
diff --git a/kcmkwin/kwinrules/ruleslist.cpp b/kcmkwin/kwinrules/ruleslist.cpp
index ae5fc68a39..c1b470414a 100644
--- a/kcmkwin/kwinrules/ruleslist.cpp
+++ b/kcmkwin/kwinrules/ruleslist.cpp
@@ -18,13 +18,14 @@
 
 #include "ruleslist.h"
 
-#include <assert.h>
 #include <QDebug>
 #include <kconfig.h>
 #include <QFileDialog>
 
 #include "ruleswidget.h"
 
+#include <cassert>
+
 namespace KWin
 {
 
diff --git a/kcmkwin/kwinrules/ruleswidget.cpp b/kcmkwin/kwinrules/ruleswidget.cpp
index 4228820ad2..8354a85bb8 100644
--- a/kcmkwin/kwinrules/ruleswidget.cpp
+++ b/kcmkwin/kwinrules/ruleswidget.cpp
@@ -31,7 +31,6 @@
 #include <kactivities/consumer.h>
 #endif
 
-#include <assert.h>
 #include <kmessagebox.h>
 #include <QTabWidget>
 #include <QTimer>
@@ -40,6 +39,8 @@
 
 #include "detectwidget.h"
 
+#include <cassert>
+
 Q_DECLARE_METATYPE(NET::WindowType)
 
 namespace KWin
diff --git a/kcmkwin/kwinscreenedges/monitor.cpp b/kcmkwin/kwinscreenedges/monitor.cpp
index 543800dffa..d1f0fb0d00 100644
--- a/kcmkwin/kwinscreenedges/monitor.cpp
+++ b/kcmkwin/kwinscreenedges/monitor.cpp
@@ -21,16 +21,16 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 #include "monitor.h"
 
-#include <QDebug>
 #include <KLocalizedString>
-#include <qgraphicsitem.h>
-#include <qgraphicsview.h>
-#include <qgraphicsscene.h>
-#include <qgraphicssceneevent.h>
-#include <qmenu.h>
-#include <qdesktopwidget.h>
-#include <qapplication.h>
-#include <plasma/framesvg.h>
+#include <Plasma/FrameSvg>
+
+#include <QApplication>
+#include <QDebug>
+#include <QDesktopWidget>
+#include <QGraphicsView>
+#include <QGraphicsScene>
+#include <QGraphicsSceneEvent>
+#include <QMenu>
 
 namespace KWin
 {
diff --git a/kcmkwin/kwinscreenedges/monitor.h b/kcmkwin/kwinscreenedges/monitor.h
index 919937da8b..c40f105730 100644
--- a/kcmkwin/kwinscreenedges/monitor.h
+++ b/kcmkwin/kwinscreenedges/monitor.h
@@ -24,9 +24,9 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 #include "screenpreviewwidget.h"
 
-#include <qactiongroup.h>
-#include <qgraphicsitem.h>
-#include <qvector.h>
+#include <QActionGroup>
+#include <QGraphicsItem>
+#include <QVector>
 
 class QAction;
 class QGraphicsView;
diff --git a/layers.cpp b/layers.cpp
index 954da9ef12..07156d9613 100644
--- a/layers.cpp
+++ b/layers.cpp
@@ -79,8 +79,6 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 */
 
-#include <assert.h>
-
 #include "utils.h"
 #include "client.h"
 #include "focuschain.h"
@@ -100,6 +98,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 #include <QDebug>
 
+#include <cassert>
+
 namespace KWin
 {
 
diff --git a/libinput/context.cpp b/libinput/context.cpp
index dd11619c3a..d9338247a9 100644
--- a/libinput/context.cpp
+++ b/libinput/context.cpp
@@ -24,9 +24,10 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "../udev.h"
 
 #include <fcntl.h>
-#include <errno.h>
 #include <unistd.h>
 
+#include <cerrno>
+
 namespace KWin
 {
 namespace LibInput
diff --git a/libkwineffects/kwinanimationeffect.h b/libkwineffects/kwinanimationeffect.h
index c8b412867a..0bbe25d74a 100644
--- a/libkwineffects/kwinanimationeffect.h
+++ b/libkwineffects/kwinanimationeffect.h
@@ -24,7 +24,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 #include <QEasingCurve>
 #include <QElapsedTimer>
-#include <qmath.h>
+#include <QtMath>
 #include <kwineffects.h>
 #include <kwineffects_export.h>
 
diff --git a/libkwineffects/kwineffects.cpp b/libkwineffects/kwineffects.cpp
index 8f70ba1b33..78f7a2b362 100644
--- a/libkwineffects/kwineffects.cpp
+++ b/libkwineffects/kwineffects.cpp
@@ -27,7 +27,6 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "kwinxrenderutils.h"
 #endif
 
-#include <qmath.h>
 #include <QVariant>
 #include <QList>
 #include <QTimeLine>
@@ -37,11 +36,12 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include <QVector2D>
 #include <QGraphicsRotation>
 #include <QGraphicsScale>
+#include <QtMath>
 
 #include <ksharedconfig.h>
 #include <kconfiggroup.h>
 
-#include <assert.h>
+#include <cassert>
 
 #include <KWayland/Server/surface_interface.h>
 
diff --git a/libkwineffects/kwineffects.h b/libkwineffects/kwineffects.h
index 7b2f3d73b8..6e8b868540 100644
--- a/libkwineffects/kwineffects.h
+++ b/libkwineffects/kwineffects.h
@@ -47,10 +47,10 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include <KPluginFactory>
 #include <KSharedConfig>
 
-#include <assert.h>
-#include <limits.h>
 #include <netwm.h>
 
+#include <cassert>
+#include <climits>
 #include <functional>
 
 class KConfigGroup;
diff --git a/libkwineffects/kwinglutils.cpp b/libkwineffects/kwinglutils.cpp
index 5dbcc54f01..b635ea3885 100644
--- a/libkwineffects/kwinglutils.cpp
+++ b/libkwineffects/kwinglutils.cpp
@@ -28,7 +28,6 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "kwinglplatform.h"
 #include "logging_p.h"
 
-
 #include <QPixmap>
 #include <QImage>
 #include <QHash>
@@ -40,10 +39,9 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include <QVarLengthArray>
 
 #include <array>
+#include <cmath>
 #include <deque>
 
-#include <math.h>
-
 #define DEBUG_GLRENDERTARGET 0
 
 #ifdef __GNUC__
diff --git a/main.cpp b/main.cpp
index 82061ef8db..943412e7cd 100644
--- a/main.cpp
+++ b/main.cpp
@@ -45,7 +45,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include <KWayland/Server/surface_interface.h>
 // Qt
 #include <qplatformdefs.h>
-#include <qcommandlineparser.h>
+#include <QCommandLineParser>
 #include <QQuickWindow>
 #include <QStandardPaths>
 #include <QtDBus>
diff --git a/placement.cpp b/placement.cpp
index 4decbaa614..220f5aae3b 100644
--- a/placement.cpp
+++ b/placement.cpp
@@ -22,11 +22,6 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 #include "placement.h"
 
-#include <QRect>
-#include <assert.h>
-
-#include <QTextStream>
-
 #ifndef KCMRULES
 #include "workspace.h"
 #include "client.h"
@@ -36,6 +31,11 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "screens.h"
 #endif
 
+#include <QRect>
+#include <QTextStream>
+
+#include <cassert>
+
 namespace KWin
 {
 
diff --git a/plugins/platforms/drm/drm_buffer.cpp b/plugins/platforms/drm/drm_buffer.cpp
index b640c593c2..a5fc83976e 100644
--- a/plugins/platforms/drm/drm_buffer.cpp
+++ b/plugins/platforms/drm/drm_buffer.cpp
@@ -23,7 +23,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 // system
 #include <sys/mman.h>
-#include <errno.h>
+// c++
+#include <cerrno>
 // drm
 #include <xf86drm.h>
 #include <xf86drmMode.h>
diff --git a/plugins/platforms/drm/drm_buffer_gbm.cpp b/plugins/platforms/drm/drm_buffer_gbm.cpp
index cbc0d3abd1..136fbb8282 100644
--- a/plugins/platforms/drm/drm_buffer_gbm.cpp
+++ b/plugins/platforms/drm/drm_buffer_gbm.cpp
@@ -25,7 +25,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 // system
 #include <sys/mman.h>
-#include <errno.h>
+// c++
+#include <cerrno>
 // drm
 #include <xf86drm.h>
 #include <xf86drmMode.h>
diff --git a/plugins/platforms/drm/drm_output.cpp b/plugins/platforms/drm/drm_output.cpp
index 7c88628bbf..c609aae27d 100644
--- a/plugins/platforms/drm/drm_output.cpp
+++ b/plugins/platforms/drm/drm_output.cpp
@@ -23,8 +23,6 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "drm_object_crtc.h"
 #include "drm_object_connector.h"
 
-#include <errno.h>
-
 #include "composite.h"
 #include "logind.h"
 #include "logging.h"
@@ -42,6 +40,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include <QMatrix4x4>
 #include <QCryptographicHash>
 #include <QPainter>
+// c++
+#include <cerrno>
 // drm
 #include <xf86drm.h>
 #include <xf86drmMode.h>
diff --git a/plugins/platforms/drm/gbm_surface.h b/plugins/platforms/drm/gbm_surface.h
index 5eaa4c908b..6c3220cbac 100644
--- a/plugins/platforms/drm/gbm_surface.h
+++ b/plugins/platforms/drm/gbm_surface.h
@@ -20,7 +20,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #ifndef KWIN_DRM_GBM_SURFACE_H
 #define KWIN_DRM_GBM_SURFACE_H
 
-#include <stdint.h>
+#include <cstdint>
 
 struct gbm_bo;
 struct gbm_device;
diff --git a/plugins/platforms/drm/remoteaccess_manager.cpp b/plugins/platforms/drm/remoteaccess_manager.cpp
index 201fd19943..abb0b37ef5 100644
--- a/plugins/platforms/drm/remoteaccess_manager.cpp
+++ b/plugins/platforms/drm/remoteaccess_manager.cpp
@@ -28,7 +28,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include <KWayland/Server/output_interface.h>
 #include <unistd.h>
 #include <gbm.h>
-#include <errno.h>
+
+#include <cerrno>
 
 namespace KWin
 {
diff --git a/plugins/platforms/x11/common/ge_event_mem_mover.h b/plugins/platforms/x11/common/ge_event_mem_mover.h
index 8b6b96db1f..2b693f409a 100644
--- a/plugins/platforms/x11/common/ge_event_mem_mover.h
+++ b/plugins/platforms/x11/common/ge_event_mem_mover.h
@@ -21,7 +21,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 #include <xcb/xcb.h>
 
-#include <string.h>
+#include <cstring>
 
 namespace KWin
 {
diff --git a/plugins/platforms/x11/standalone/glxbackend.cpp b/plugins/platforms/x11/standalone/glxbackend.cpp
index 1d31b447f9..c6579c617a 100644
--- a/plugins/platforms/x11/standalone/glxbackend.cpp
+++ b/plugins/platforms/x11/standalone/glxbackend.cpp
@@ -51,7 +51,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #if HAVE_DL_LIBRARY
 #include <dlfcn.h>
 #endif
-#include <assert.h>
+#include <cassert>
 
 #ifndef XCB_GLX_BUFFER_SWAP_COMPLETE
 #define XCB_GLX_BUFFER_SWAP_COMPLETE 1
diff --git a/plugins/platforms/x11/standalone/overlaywindow_x11.cpp b/plugins/platforms/x11/standalone/overlaywindow_x11.cpp
index 5a787665fb..c8125a96d6 100644
--- a/plugins/platforms/x11/standalone/overlaywindow_x11.cpp
+++ b/plugins/platforms/x11/standalone/overlaywindow_x11.cpp
@@ -26,10 +26,10 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "utils.h"
 #include "xcbutils.h"
 
-#include "assert.h"
-
 #include <QVector>
 
+#include <cassert>
+
 #include <xcb/composite.h>
 #include <xcb/shape.h>
 #if XCB_COMPOSITE_MAJOR_VERSION > 0 || XCB_COMPOSITE_MINOR_VERSION >= 3
diff --git a/plugins/scenes/opengl/lanczosfilter.cpp b/plugins/scenes/opengl/lanczosfilter.cpp
index c02158dd65..f70c2c12a5 100644
--- a/plugins/scenes/opengl/lanczosfilter.cpp
+++ b/plugins/scenes/opengl/lanczosfilter.cpp
@@ -36,8 +36,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include <kwineffects.h>
 
 #include <QFile>
+#include <QtMath>
 
-#include <qmath.h>
 #include <cmath>
 
 namespace KWin
diff --git a/plugins/scenes/opengl/scene_opengl.cpp b/plugins/scenes/opengl/scene_opengl.cpp
index 8da2d358df..6c3a083000 100644
--- a/plugins/scenes/opengl/scene_opengl.cpp
+++ b/plugins/scenes/opengl/scene_opengl.cpp
@@ -53,14 +53,14 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 #include <array>
 #include <cmath>
+#include <cstddef>
 #include <unistd.h>
-#include <stddef.h>
 
-#include <qpainter.h>
 #include <QDBusConnection>
 #include <QDBusConnectionInterface>
 #include <QDBusInterface>
 #include <QGraphicsScale>
+#include <QPainter>
 #include <QStringList>
 #include <QVector2D>
 #include <QVector4D>
diff --git a/plugins/scenes/xrender/scene_xrender.cpp b/plugins/scenes/xrender/scene_xrender.cpp
index 30911f15a1..38bb8c97c5 100644
--- a/plugins/scenes/xrender/scene_xrender.cpp
+++ b/plugins/scenes/xrender/scene_xrender.cpp
@@ -43,7 +43,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 #include <QDebug>
 #include <QPainter>
-#include <qmath.h>
+#include <QtMath>
 
 namespace KWin
 {
diff --git a/shadow.h b/shadow.h
index 399b9f446b..df92c2883b 100644
--- a/shadow.h
+++ b/shadow.h
@@ -23,7 +23,6 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include <QObject>
 #include <QPixmap>
 #include <kwineffects.h>
-#include <qvarlengtharray.h>
 
 namespace KDecoration2
 {
diff --git a/shell_client.cpp b/shell_client.cpp
index d3a7b0da3c..ca7e246437 100644
--- a/shell_client.cpp
+++ b/shell_client.cpp
@@ -58,7 +58,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 #include <sys/types.h>
 #include <unistd.h>
-#include <signal.h>
+
+#include <csignal>
 
 Q_DECLARE_METATYPE(NET::WindowType)
 
diff --git a/sm.cpp b/sm.cpp
index dd4cc89f0b..cb39bec8e6 100644
--- a/sm.cpp
+++ b/sm.cpp
@@ -22,7 +22,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "sm.h"
 
 #include <unistd.h>
-#include <stdlib.h>
+#include <cstdlib>
 #include <pwd.h>
 #include <fixx11h.h>
 #include <kconfig.h>
diff --git a/tabbox/clientmodel.cpp b/tabbox/clientmodel.cpp
index 7a7625095e..048677f188 100644
--- a/tabbox/clientmodel.cpp
+++ b/tabbox/clientmodel.cpp
@@ -30,7 +30,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include <QTextDocument>
 #include <QTextStream>
 // other
-#include <math.h>
+#include <cmath>
 
 namespace KWin
 {
diff --git a/tabbox/desktopmodel.cpp b/tabbox/desktopmodel.cpp
index dbb4a70147..41949ebf20 100644
--- a/tabbox/desktopmodel.cpp
+++ b/tabbox/desktopmodel.cpp
@@ -24,7 +24,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "tabboxconfig.h"
 #include "tabboxhandler.h"
 
-#include <math.h>
+#include <cmath>
 
 namespace KWin
 {
diff --git a/tests/normalhintsbasesizetest.cpp b/tests/normalhintsbasesizetest.cpp
index 54ac0e448b..ed0136c932 100644
--- a/tests/normalhintsbasesizetest.cpp
+++ b/tests/normalhintsbasesizetest.cpp
@@ -17,7 +17,7 @@
  * You should have received a copy of the GNU General Public License
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
-#include <stdlib.h>
+#include <cstdlib>
 #include <iostream>
 #include <xcb/xcb.h>
 #include <xcb/xcb_icccm.h>
diff --git a/toplevel.h b/toplevel.h
index 97e90f2064..fe32ae056e 100644
--- a/toplevel.h
+++ b/toplevel.h
@@ -38,9 +38,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 // XLib
 #include <X11/Xlib.h>
 #include <fixx11h.h>
-// system
-#include <assert.h>
 // c++
+#include <cassert>
 #include <functional>
 
 class QOpenGLFramebufferObject;
diff --git a/utils.cpp b/utils.cpp
index 91f345a7d6..45d5d0e83c 100644
--- a/utils.cpp
+++ b/utils.cpp
@@ -31,19 +31,18 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include <kkeyserver.h>
 
 #ifndef KCMRULES
-#include <assert.h>
 #include <QApplication>
 #include <QDebug>
 
 #include <X11/Xlib.h>
 
-#include <stdio.h>
-
 #include "atoms.h"
 #include "platform.h"
 #include "workspace.h"
 
-#include <signal.h>
+#include <cassert>
+#include <csignal>
+#include <cstdio>
 
 #endif
 
diff --git a/utils.h b/utils.h
index 22491d5568..459cae8dfa 100644
--- a/utils.h
+++ b/utils.h
@@ -37,7 +37,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include <QScopedPointer>
 #include <QProcess>
 // system
-#include <limits.h>
+#include <climits>
 Q_DECLARE_LOGGING_CATEGORY(KWIN_CORE)
 Q_DECLARE_LOGGING_CATEGORY(KWIN_VIRTUALKEYBOARD)
 namespace KWin
diff --git a/virtual_terminal.cpp b/virtual_terminal.cpp
index 8ceb74d3ad..ecdf9d1d10 100644
--- a/virtual_terminal.cpp
+++ b/virtual_terminal.cpp
@@ -32,11 +32,12 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 // system
 #include <fcntl.h>
 #include <unistd.h>
-#include <signal.h>
 #include <sys/ioctl.h>
 #include <sys/signalfd.h>
 #include <sys/stat.h>
 #include <sys/sysmacros.h>
+// c++
+#include <csignal>
 
 #define RELEASE_SIGNAL SIGUSR1
 #define ACQUISITION_SIGNAL SIGUSR2