diff --git a/toonz/sources/tcleanupper/tcleanupper.cpp b/toonz/sources/tcleanupper/tcleanupper.cpp
index 88b0a6b..48a4aa6 100644
--- a/toonz/sources/tcleanupper/tcleanupper.cpp
+++ b/toonz/sources/tcleanupper/tcleanupper.cpp
@@ -316,11 +316,16 @@ void searchLevelsToCleanup(
 			}
 		}
 	}
+
 	assert(levelTable.size() == framesTable.size());
-	std::map<wstring, TXshSimpleLevel *>::iterator it1 = levelTable.begin();
-	std::map<wstring, std::set<TFrameId>>::iterator it2 = framesTable.begin();
-	for (it1; it1 != levelTable.end(); ++it1, ++it2)
-		levels.push_back(std::make_pair(it1->second, it2->second));
+
+	for (auto const& level : levelTable) {
+		auto const it = framesTable.find(level.first);
+		if (it == framesTable.end()) {
+			continue;
+		}
+		levels.push_back(std::make_pair(level.second, (*it).second));
+	}
 }
 
 //------------------------------------------------------------------------------
@@ -413,10 +418,7 @@ void cleanupLevel(TXshSimpleLevel *xl, std::set<TFrameId> fidsInXsheet,
 	m_userLog.info(info);
 	DVGui::info(QString::fromStdString(info));
 	bool firstImage = true;
-	std::set<TFrameId>::iterator it = fidsInXsheet.begin();
-	for (it; it != fidsInXsheet.end(); it++) {
-		TFrameId fid = *it;
-
+	for (auto const& fid : fidsInXsheet) {
 		cout << "  " << fid << endl;
 		info = "  " + fid.expand();
 		m_userLog.info(info);
diff --git a/toonz/sources/tnztools/vectorselectiontool.cpp b/toonz/sources/tnztools/vectorselectiontool.cpp
index ab9a31e..da86621 100644
--- a/toonz/sources/tnztools/vectorselectiontool.cpp
+++ b/toonz/sources/tnztools/vectorselectiontool.cpp
@@ -211,20 +211,23 @@ void VectorFreeDeformer::deformRegions()
 
 void VectorFreeDeformer::deformImage()
 {
-	assert(int(m_strokeIndexes.size()) == int(m_originalStrokes.size()));
+	// debug
+	assert(m_strokeIndexes.size() == m_originalStrokes.size());
 
-	QMutexLocker lock(m_vi->getMutex());
+	// release
+	if (m_strokeIndexes.size() != m_originalStrokes.size()) {
+		return;
+	}
 
-	std::set<int>::iterator it1 = m_strokeIndexes.begin();
-	std::vector<TStroke *>::iterator it2 = m_originalStrokes.begin();
+	QMutexLocker lock(m_vi->getMutex());
 
-	for (it1; it1 != m_strokeIndexes.end(); ++it1, ++it2) {
-		TStroke *stroke = m_vi->getStroke(*it1);
-		TStroke *originalStroke = *it2;
+	std::size_t i = 0;
+	for (auto it = m_strokeIndexes.begin(), end = m_strokeIndexes.end(); it != end; ++it) {
+		TStroke *stroke = m_vi->getStroke(*it);
+		TStroke *originalStroke = m_originalStrokes[i++];
 
 		assert(stroke->getControlPointCount() == originalStroke->getControlPointCount());
-		int j;
-		for (j = 0; j < stroke->getControlPointCount(); j++) {
+		for (int j = 0, count = stroke->getControlPointCount(); j < count; ++j) {
 			TThickPoint p = deform(originalStroke->getControlPoint(j));
 			stroke->setControlPoint(j, p);
 		}
diff --git a/toonz/sources/toonz/adjustlevelspopup.cpp b/toonz/sources/toonz/adjustlevelspopup.cpp
index 02c8914..e1e3d4b 100644
--- a/toonz/sources/toonz/adjustlevelspopup.cpp
+++ b/toonz/sources/toonz/adjustlevelspopup.cpp
@@ -731,9 +731,8 @@ void AdjustLevelsPopup::apply()
 			std::set<TFrameId> fids = filmstripSelection->getSelectedFids();
 			bool oneImageChanged = false;
 
-			std::set<TFrameId>::iterator it = fids.begin();
-			for (it; it != fids.end(); it++) {
-				TRasterImageP rasImage = (TRasterImageP)simpleLevel->getFrame(*it, true);
+			for (auto const& fid : fids) {
+				TRasterImageP rasImage = (TRasterImageP)simpleLevel->getFrame(fid, true);
 				if (!rasImage)
 					continue;
 
@@ -744,10 +743,10 @@ void AdjustLevelsPopup::apply()
 				oneImageChanged = true;
 				TRop::rgbmAdjust(ras, ras, in0, in1, out0, out1);
 
-				simpleLevel->touchFrame(*it);
+				simpleLevel->touchFrame(fid);
 				simpleLevel->setDirtyFlag(true);
 
-				IconGenerator::instance()->invalidate(simpleLevel, *it);
+				IconGenerator::instance()->invalidate(simpleLevel, fid);
 			}
 
 			if (oneImageChanged) {
diff --git a/toonz/sources/toonz/antialiaspopup.cpp b/toonz/sources/toonz/antialiaspopup.cpp
index 923e608..f78b406 100644
--- a/toonz/sources/toonz/antialiaspopup.cpp
+++ b/toonz/sources/toonz/antialiaspopup.cpp
@@ -388,10 +388,9 @@ void AntialiasPopup::apply()
 		TXshSimpleLevel *simpleLevel = TApp::instance()->getCurrentLevel()->getSimpleLevel();
 		if (simpleLevel) {
 			std::set<TFrameId> fids = filmstripSelection->getSelectedFids();
-			std::set<TFrameId>::iterator it = fids.begin();
 			bool oneImageChanged = false;
-			for (it; it != fids.end(); it++) {
-				TImageP image = simpleLevel->getFrame(*it, true);
+			for (auto const fid : fids) {
+				TImageP image = simpleLevel->getFrame(fid, true);
 				if (!image)
 					continue;
 				TRasterP ras = image->raster();
@@ -399,9 +398,9 @@ void AntialiasPopup::apply()
 					continue;
 				oneImageChanged = true;
 				onChange(ras, threshold, softness);
-				simpleLevel->touchFrame(*it);
+				simpleLevel->touchFrame(fid);
 				simpleLevel->setDirtyFlag(true);
-				IconGenerator::instance()->invalidate(simpleLevel, *it);
+				IconGenerator::instance()->invalidate(simpleLevel, fid);
 			}
 			if (oneImageChanged) {
 				close();
diff --git a/toonz/sources/toonz/brightnessandcontrastpopup.cpp b/toonz/sources/toonz/brightnessandcontrastpopup.cpp
index adfd694..2e61c9d 100644
--- a/toonz/sources/toonz/brightnessandcontrastpopup.cpp
+++ b/toonz/sources/toonz/brightnessandcontrastpopup.cpp
@@ -512,8 +512,8 @@ void BrightnessAndContrastPopup::apply()
 			std::set<TFrameId> fids = filmstripSelection->getSelectedFids();
 			std::set<TFrameId>::iterator it = fids.begin();
 			bool oneImageChanged = false;
-			for (it; it != fids.end(); it++) {
-				TRasterImageP rasImage = (TRasterImageP)simpleLevel->getFrame(*it, true);
+			for (auto const& fid : fids) {
+				TRasterImageP rasImage = (TRasterImageP)simpleLevel->getFrame(fid, true);
 				;
 				if (!rasImage)
 					continue;
@@ -522,9 +522,9 @@ void BrightnessAndContrastPopup::apply()
 					continue;
 				oneImageChanged = true;
 				onChange(ras, contrast, brightness);
-				simpleLevel->touchFrame(*it);
+				simpleLevel->touchFrame(fid);
 				simpleLevel->setDirtyFlag(true);
-				IconGenerator::instance()->invalidate(simpleLevel, *it);
+				IconGenerator::instance()->invalidate(simpleLevel, fid);
 			}
 			if (oneImageChanged) {
 				close();
diff --git a/toonz/sources/toonz/castviewer.cpp b/toonz/sources/toonz/castviewer.cpp
index 3d1b1e1..318923c 100644
--- a/toonz/sources/toonz/castviewer.cpp
+++ b/toonz/sources/toonz/castviewer.cpp
@@ -582,12 +582,10 @@ void CastBrowser::sortByDataModel(DataType dataType, bool isDiscendent)
 	if (isDiscendentOrder() != isDiscendent) {
 		setIsDiscendentOrder(isDiscendent);
 		std::vector<CastItem *> items;
-		int i = 0;
-		for (i; i < m_castItems->getItemCount(); i++)
+		for (int i = 0; i < m_castItems->getItemCount(); i++)
 			items.push_back(m_castItems->getItem(i)->clone());
 		m_castItems->clear();
-		i = items.size() - 1;
-		for (i; i >= 0; i--)
+		for (int i = items.size() - 1; i >= 0; i--)
 			m_castItems->addItem(items[i]);
 	}
 
@@ -826,10 +824,9 @@ QMenu *CastBrowser::getContextMenu(QWidget *parent, int index)
 void CastBrowser::expose()
 {
 	std::set<int> selectedIndices = m_itemViewer->getPanel()->getSelectedIndices();
-	std::set<int>::iterator it = selectedIndices.begin();
 	TUndoManager::manager()->beginBlock();
-	for (it; it != selectedIndices.end(); it++) {
-		CastItem *item = m_castItems->getItem(*it);
+	for (int index : selectedIndices) {
+		CastItem *item = m_castItems->getItem(index);
 		TXshSimpleLevel *sl = item->getSimpleLevel();
 		TXshPaletteLevel *pl = item->getPaletteLevel();
 		TXshSoundLevel *soundl = item->getSoundLevel();
diff --git a/toonz/sources/toonz/cellselection.cpp b/toonz/sources/toonz/cellselection.cpp
index d91918b..d6cd5ea 100644
--- a/toonz/sources/toonz/cellselection.cpp
+++ b/toonz/sources/toonz/cellselection.cpp
@@ -609,9 +609,9 @@ bool pasteStrokesInCellWithoutUndo(int row, int col, const StrokesData *strokesD
 	if (vi) {
 		std::set<int> indicesSet;
 		strokesData->getImage(vi, indicesSet, true);
-		std::set<int>::iterator it = indicesSet.begin();
-		for (it; it != indicesSet.end(); it++)
-			indices.push_back(*it);
+		for (int index : indicesSet) {
+			indices.push_back(index);
+		}
 		assert(sl);
 		app->getPaletteController()->getCurrentLevelPalette()->notifyPaletteChanged();
 		IconGenerator::instance()->invalidate(sl, fid);
diff --git a/toonz/sources/toonz/drawingdata.cpp b/toonz/sources/toonz/drawingdata.cpp
index d5c4022..b0bd275 100644
--- a/toonz/sources/toonz/drawingdata.cpp
+++ b/toonz/sources/toonz/drawingdata.cpp
@@ -274,18 +274,16 @@ bool DrawingData::getLevelFrames(TXshSimpleLevel *sl,
 	TPaletteP imgPlt;
 	// selected frames
 	std::set<TFrameId>::iterator it = framesToInsert.begin();
-	// copied frames
-	std::map<TFrameId, QString>::const_iterator mapIt = m_imageSet.begin();
 
 	//Preprocessing to keep used styles
-	for (mapIt; mapIt != m_imageSet.end(); ++mapIt) {
-		QString imageId = mapIt->second;
+	for (auto const& image : m_imageSet) {
+		QString imageId = image.second;
 		// paste destination
 		TFrameId frameId;
 
 		//merge
 		if (setType == OVER_FRAMEID) //If setType == OVER_FRAMEID ignore frames
-			frameId = mapIt->first;
+			frameId = image.first;
 		else {
 			// if type == OVER_SELECTION, pasting ends at the end of selected range
 			if (it == framesToInsert.end())
@@ -315,12 +313,12 @@ bool DrawingData::getLevelFrames(TXshSimpleLevel *sl,
 		styleTable[s] = s;
 
 	//Merge Image
-	for (mapIt = usedImageSet.begin(); mapIt != usedImageSet.end(); ++mapIt) {
-		QString imageId = mapIt->second;
+	for (auto const& image : usedImageSet) {
+		QString imageId = image.second;
 		TImageP img = getImage(imageId, sl, styleTable);
 		if (!cloneImages)
 			TImageCache::instance()->remove(imageId);
-		sl->setFrame(mapIt->first, cloneImages ? img->cloneImage() : img);
+		sl->setFrame(image.first, cloneImages ? img->cloneImage() : img);
 	}
 
 	//merge Hooks
@@ -329,17 +327,18 @@ bool DrawingData::getLevelFrames(TXshSimpleLevel *sl,
 	int hookCount = m_levelHooks.getHookCount();
 	//shiftHooks(sl,usedImageSet.begin()->first,framesToInsert.size());
 
-	std::map<TFrameId, QString>::const_iterator frameIt = m_imageSet.begin();
-	for (mapIt = usedImageSet.begin(); mapIt != usedImageSet.end(); ++mapIt, ++frameIt) {
+	auto frameIt = m_imageSet.begin();
+	for (auto const& image : usedImageSet) {
 		for (int i = 0; i < hookCount; i++) {
 			Hook *levelHook = levelHooks->getHook(i);
 			if (!levelHook)
 				levelHook = levelHooks->addHook();
 			Hook *copiedHook = m_levelHooks.getHook(i);
 			assert(copiedHook);
-			levelHook->setAPos(mapIt->first, copiedHook->getAPos(frameIt->first));
-			levelHook->setBPos(mapIt->first, copiedHook->getBPos(frameIt->first));
+			levelHook->setAPos(image.first, copiedHook->getAPos((*frameIt).first));
+			levelHook->setBPos(image.first, copiedHook->getBPos((*frameIt).first));
 		}
+		++frameIt;
 	}
 
 	sl->setDirtyFlag(true);
@@ -435,9 +434,8 @@ void DrawingData::setFrames(const std::map<TFrameId, QString> &imageSet, TXshSim
 
 void DrawingData::getFrames(std::set<TFrameId> &frames) const
 {
-	std::map<TFrameId, QString>::const_iterator mapIt = m_imageSet.begin();
-	for (mapIt; mapIt != m_imageSet.end(); ++mapIt)
-		frames.insert(mapIt->first);
+	for (auto const& image : m_imageSet)
+		frames.insert(image.first);
 }
 
 //-----------------------------------------------------------------------------
diff --git a/toonz/sources/toonz/filebrowser.cpp b/toonz/sources/toonz/filebrowser.cpp
index 899b112..52f3fc4 100644
--- a/toonz/sources/toonz/filebrowser.cpp
+++ b/toonz/sources/toonz/filebrowser.cpp
@@ -1503,9 +1503,9 @@ bool FileBrowser::drop(const QMimeData *mimeData)
 		newSl->setPalette(sl->getPalette());
 		newSl->setScene(sl->getScene());
 		std::set<TFrameId> frames = s->getSelectedFids();
-		std::set<TFrameId>::iterator it = frames.begin();
-		for (it; it != frames.end(); it++)
-			newSl->setFrame(*it, sl->getFrame(*it, false));
+		for (auto const& fid : frames) {
+			newSl->setFrame(fid, sl->getFrame(fid, false));
+		}
 
 		IoCmd::saveLevel(folderPath, newSl, false);
 		refreshFolder(folderPath.getParentDir());
diff --git a/toonz/sources/toonz/filmstripcommand.cpp b/toonz/sources/toonz/filmstripcommand.cpp
index c2afc07..9ce6d0c 100644
--- a/toonz/sources/toonz/filmstripcommand.cpp
+++ b/toonz/sources/toonz/filmstripcommand.cpp
@@ -416,17 +416,16 @@ void insertNotEmptyframes(const TXshSimpleLevelP &sl,
 	std::vector<TFrameId> fids;
 	sl->getFids(fids);
 	std::set<TFrameId> frames;
-	std::map<TFrameId, QString>::const_iterator it = framesToInsert.begin();
-	for (it; it != framesToInsert.end(); it++)
-		frames.insert(it->first);
+	for (auto const& frame : framesToInsert) {
+		frames.insert(frame.first);
+	}
 	makeSpaceForFids(sl.getPointer(), frames);
 
-	for (it = framesToInsert.begin(); it != framesToInsert.end(); ++it) {
-		//QString cacheId = "UndoImage"+QString::number(id)+"-"+QString::number(it->first.getNumber());
-		TImageP img = TImageCache::instance()->get(it->second, false);
-		TImageCache::instance()->remove(it->second);
+	for (auto const& frame : framesToInsert) {
+		TImageP img = TImageCache::instance()->get(frame.second, false);
+		TImageCache::instance()->remove(frame.second);
 		assert(img);
-		sl->setFrame(it->first, img);
+		sl->setFrame(frame.first, img);
 	}
 	invalidateIcons(sl.getPointer(), frames);
 	sl->setDirtyFlag(true);
@@ -1203,10 +1202,9 @@ public:
 	{
 		makeSpaceForFids(m_level.getPointer(), m_insertedFids);
 
-		std::set<TFrameId>::const_iterator it = m_insertedFids.begin();
-		for (it; it != m_insertedFids.end(); it++) {
-			m_level->setFrame(*it, m_level->createEmptyFrame());
-			IconGenerator::instance()->invalidate(m_level.getPointer(), *it);
+		for (auto const& fid : m_insertedFids) {
+			m_level->setFrame(fid, m_level->createEmptyFrame());
+			IconGenerator::instance()->invalidate(m_level.getPointer(), fid);
 		}
 		m_level->setDirtyFlag(true);
 
@@ -1261,10 +1259,9 @@ void FilmstripCmd::addFrames(TXshSimpleLevel *sl, int start, int end, int step)
 
 	makeSpaceForFids(sl, fidsToInsert);
 
-	std::set<TFrameId>::iterator it = fidsToInsert.begin();
-	for (it; it != fidsToInsert.end(); it++) {
-		sl->setFrame(*it, sl->createEmptyFrame());
-		IconGenerator::instance()->invalidate(sl, *it);
+	for (auto const& fid : fidsToInsert) {
+		sl->setFrame(fid, sl->createEmptyFrame());
+		IconGenerator::instance()->invalidate(sl, fid);
 	}
 	sl->setDirtyFlag(true);
 
@@ -2305,15 +2302,11 @@ void FilmstripCmd::duplicate(TXshSimpleLevel *sl, std::set<TFrameId> &frames, bo
 
 	std::map<TFrameId, QString> framesToInsert;
 	std::set<TFrameId> newFrames;
-	std::set<TFrameId>::iterator it = frames.begin();
 	int i = 0;
-	for (it; it != frames.end(); it++) {
-		TFrameId fid = *it;
-		TImageP img = sl->getFrame(*it, false);
+	for (auto const& fid : frames) {
+		TImageP img = sl->getFrame(fid, false);
 		TImageP imgClone = (img) ? img->cloneImage() : 0;
-		//QString id = "dupFrames"+QString::number((UINT)sl)+"-"+QString::number(it->getNumber());
-		QString id = "dupFrames" + QString::number((uintptr_t)sl) + "-" + QString::number(it->getNumber());
-		//TImageCache::instance()->add(id, sl->getFrame(*it, false));
+		QString id = "dupFrames" + QString::number((uintptr_t)sl) + "-" + QString::number(fid.getNumber());
 		TImageCache::instance()->add(id, imgClone);
 		framesToInsert[insertPoint + i] = id;
 		newFrames.insert(insertPoint + i);
@@ -2624,11 +2617,10 @@ void FilmstripCmd::inbetween(TXshSimpleLevel *sl,
 	std::vector<TFrameId> fids;
 	std::vector<TFrameId> levelFids;
 	sl->getFids(levelFids);
-	std::vector<TFrameId>::iterator it = levelFids.begin();
-	for (it; it != levelFids.end(); it++) {
-		int curFid = it->getNumber();
+	for (auto const &fid : levelFids) {
+		int curFid = fid.getNumber();
 		if (fid0.getNumber() <= curFid && curFid <= fid1.getNumber())
-			fids.push_back(*it);
+			fids.push_back(fid);
 	}
 
 	TUndoManager::manager()->add(new UndoInbetween(sl, fids, interpolation));
diff --git a/toonz/sources/toonz/keyframedata.cpp b/toonz/sources/toonz/keyframedata.cpp
index 935d2cf..ac7e926 100644
--- a/toonz/sources/toonz/keyframedata.cpp
+++ b/toonz/sources/toonz/keyframedata.cpp
@@ -98,11 +98,10 @@ bool TKeyframeData::getKeyframes(std::set<Position> &positions, TXsheet *xsh) co
 	if (!keyFrameChanged)
 		return false;
 
-	std::map<int, bool>::const_iterator it1 = m_isPegbarsCycleEnabled.begin();
-	for (it1; it1 != m_isPegbarsCycleEnabled.end(); it1++) {
-		int col = it1->first;
-		TStageObject *pegbar = xsh->getStageObject(col >= 0 ? TStageObjectId::ColumnId(col) : cameraId);
-		pegbar->enableCycle(it1->second);
+	for (auto const pegbar : m_isPegbarsCycleEnabled) {
+		int const col = pegbar.first;
+		TStageObjectId objectId = (col >= 0) ? TStageObjectId::ColumnId(col) : cameraId;
+		xsh->getStageObject(objectId)->enableCycle(pegbar.second);
 	}
 	return true;
 }
diff --git a/toonz/sources/toonz/keyframemover.cpp b/toonz/sources/toonz/keyframemover.cpp
index b646866..0e39fab 100644
--- a/toonz/sources/toonz/keyframemover.cpp
+++ b/toonz/sources/toonz/keyframemover.cpp
@@ -50,16 +50,15 @@ void KeyframeMover::setKeyframes()
 {
 	TXsheet *xsh = getXsheet();
 	std::set<KeyframePosition>::iterator posIt;
-	std::set<KeyframePosition>::iterator it = m_lastKeyframes.begin();
-	for (it; it != m_lastKeyframes.end(); it++) {
-		int c = it->second;
+	for (auto const& key : m_lastKeyframes) {
+		int c = key.second;
 		TStageObjectId objId = c >= 0 ? TStageObjectId::ColumnId(c) : TStageObjectId::CameraId(0);
 		TStageObject *stObj = xsh->getStageObject(objId);
 		TStageObject::KeyframeMap keyframes;
 		stObj->getKeyframes(keyframes);
-		TStageObject::KeyframeMap::iterator it2 = keyframes.begin();
-		for (it2; it2 != keyframes.end(); it2++)
-			stObj->removeKeyframeWithoutUndo(it2->first);
+		for (auto const& frame : keyframes) {
+			stObj->removeKeyframeWithoutUndo(frame.first);
+		}
 	}
 	m_lastKeyframeData->getKeyframes(m_lastKeyframes, xsh);
 }
@@ -69,17 +68,16 @@ void KeyframeMover::setKeyframes()
 void KeyframeMover::getKeyframes()
 {
 	TXsheet *xsh = getXsheet();
-	std::set<TKeyframeSelection::Position>::iterator it = m_startSelectedKeyframes.begin();
-	for (it; it != m_startSelectedKeyframes.end(); it++) {
-		int c = it->second;
+	for (auto const& pos : m_startSelectedKeyframes) {
+		int c = pos.second;
 		TStageObjectId objId = c >= 0 ? TStageObjectId::ColumnId(c) : TStageObjectId::CameraId(0);
 		TStageObject *stObj = xsh->getStageObject(objId);
-		assert(stObj->isKeyframe(it->first));
+		assert(stObj->isKeyframe(pos.first));
 		TStageObject::KeyframeMap keyframes;
 		stObj->getKeyframes(keyframes);
-		TStageObject::KeyframeMap::iterator it2 = keyframes.begin();
-		for (it2; it2 != keyframes.end(); it2++)
-			m_lastKeyframes.insert(KeyframePosition(it2->first, c));
+		for (auto const& frame : keyframes) {
+			m_lastKeyframes.insert(KeyframePosition(frame.first, c));
+		}
 	}
 
 	if (m_lastKeyframeData) {
diff --git a/toonz/sources/toonz/levelcommand.cpp b/toonz/sources/toonz/levelcommand.cpp
index c8e99f8..6b7fd4e 100644
--- a/toonz/sources/toonz/levelcommand.cpp
+++ b/toonz/sources/toonz/levelcommand.cpp
@@ -277,9 +277,7 @@ public:
 		: m_sl(sl), m_selectedFids(selectedFids), m_isCleanedUp(isCleanedUp)
 	{
 		static int revertToCommandCount = 0;
-		std::set<TFrameId>::const_iterator it = m_selectedFids.begin();
-		for (it; it != m_selectedFids.end(); it++) {
-			TFrameId fid = *it;
+		for (auto const& fid : m_selectedFids) {
 			if (!sl->isFid(fid))
 				continue;
 			TImageP image = sl->getFrame(fid, false);
@@ -302,9 +300,7 @@ public:
 	{
 		assert((int)m_replacedImgsId.size() == (int)m_selectedFids.size());
 		int i = 0;
-		std::set<TFrameId>::const_iterator it = m_selectedFids.begin();
-		for (it; it != m_selectedFids.end(); it++, i++) {
-			TFrameId fid = *it;
+		for (auto const& fid : m_selectedFids) {
 			QString imageId = m_replacedImgsId[i];
 			TImageP img = TImageCache::instance()->get(imageId, false)->cloneImage();
 			if (!img.getPointer())
@@ -403,8 +399,7 @@ void revertTo(bool isCleanedUp)
 		TUndoManager::manager()->beginBlock();
 		std::set<TXshSimpleLevel *>::iterator it = levels.begin();
 		/*-- Revert対象の各レベルについて --*/
-		for (it; it != levels.end(); it++) {
-			TXshSimpleLevel *sl = *it;
+		for (auto const sl : levels) {
 			std::set<TFrameId> selectedFids;
 			/*- 選択範囲のFrameIdを取得する -*/
 			getLevelSelectedFids(selectedFids, *it, r0, c0, r1, c1);
diff --git a/toonz/sources/toonz/levelsettingspopup.cpp b/toonz/sources/toonz/levelsettingspopup.cpp
index fc69701..8b39165 100644
--- a/toonz/sources/toonz/levelsettingspopup.cpp
+++ b/toonz/sources/toonz/levelsettingspopup.cpp
@@ -695,9 +695,9 @@ void LevelSettingsPopup::onPathChanged()
 			m_sl->invalidateFrames();
 			std::vector<TFrameId> frames;
 			m_sl->getFids(frames);
-			std::vector<TFrameId>::iterator it = frames.begin();
-			for (it; it != frames.end(); it++)
-				IconGenerator::instance()->invalidate(m_sl.getPointer(), *it);
+			for (auto const& fid : frames) {
+				IconGenerator::instance()->invalidate(m_sl.getPointer(), fid);
+			}
 			return;
 		}
 	}
@@ -719,9 +719,9 @@ void LevelSettingsPopup::onPathChanged()
 	m_sl->invalidateFrames();
 	std::vector<TFrameId> frames;
 	m_sl->getFids(frames);
-	std::vector<TFrameId>::iterator it = frames.begin();
-	for (it; it != frames.end(); it++)
-		IconGenerator::instance()->invalidate(m_sl.getPointer(), *it);
+	for (auto const& fid : frames) {
+		IconGenerator::instance()->invalidate(m_sl.getPointer(), fid);
+	}
 	updateLevelSettings();
 }
 
diff --git a/toonz/sources/toonz/linesfadepopup.cpp b/toonz/sources/toonz/linesfadepopup.cpp
index a7c11e4..85702ef 100644
--- a/toonz/sources/toonz/linesfadepopup.cpp
+++ b/toonz/sources/toonz/linesfadepopup.cpp
@@ -402,10 +402,9 @@ void LinesFadePopup::apply()
 		TXshSimpleLevel *simpleLevel = TApp::instance()->getCurrentLevel()->getSimpleLevel();
 		if (simpleLevel) {
 			std::set<TFrameId> fids = filmstripSelection->getSelectedFids();
-			std::set<TFrameId>::iterator it = fids.begin();
 			bool oneImageChanged = false;
-			for (it; it != fids.end(); it++) {
-				TRasterImageP rasImage = (TRasterImageP)simpleLevel->getFrame(*it, true);
+			for (auto const& fid : fids) {
+				TRasterImageP rasImage = (TRasterImageP)simpleLevel->getFrame(fid, true);
 				;
 				if (!rasImage)
 					continue;
@@ -414,9 +413,9 @@ void LinesFadePopup::apply()
 					continue;
 				oneImageChanged = true;
 				onChange(ras, ras, color, intensity);
-				simpleLevel->touchFrame(*it);
+				simpleLevel->touchFrame(fid);
 				simpleLevel->setDirtyFlag(true);
-				IconGenerator::instance()->invalidate(simpleLevel, *it);
+				IconGenerator::instance()->invalidate(simpleLevel, fid);
 			}
 			if (oneImageChanged) {
 				close();
diff --git a/toonz/sources/toonz/magpiefileimportpopup.cpp b/toonz/sources/toonz/magpiefileimportpopup.cpp
index 8223d9a..04d9f5a 100644
--- a/toonz/sources/toonz/magpiefileimportpopup.cpp
+++ b/toonz/sources/toonz/magpiefileimportpopup.cpp
@@ -225,8 +225,7 @@ void MagpieFileImportPopup::onOkPressed()
 	QList<QString> commentList;
 	int commentCount = comments.size();
 	int actorActsCount = actorActs.size();
-	int i = from;
-	for (i; i <= to; i++) {
+	for (int i = from; i <= to; i++) {
 		if (commentCount <= i || actorActsCount <= i)
 			continue;
 		commentList.append(comments.at(i));
@@ -235,8 +234,7 @@ void MagpieFileImportPopup::onOkPressed()
 			frameList.push_back(TFrameId());
 			continue;
 		}
-		int j;
-		for (j = 0; j < m_actFields.size(); j++) {
+		for (int j = 0; j < m_actFields.size(); j++) {
 			DVGui::IntLineEdit *field = m_actFields.at(j).second;
 			QString act = field->property("act").toString();
 			if (actorAct != act)
diff --git a/toonz/sources/toonz/mainwindow.cpp b/toonz/sources/toonz/mainwindow.cpp
index bc86972..55e749e 100644
--- a/toonz/sources/toonz/mainwindow.cpp
+++ b/toonz/sources/toonz/mainwindow.cpp
@@ -1099,11 +1099,11 @@ void MainWindow::resetRoomsLayout()
 		try {
 			TFilePathSet fpset;
 			TSystem::readDirectory(fpset, layoutDir, true, false);
-			TFilePathSet::iterator it = fpset.begin();
-			for (it; it != fpset.end(); it++) {
-				QString fn = toQString((*it).withoutParentDir());
-				if (fn.startsWith("room") || fn.startsWith("popups"))
-					TSystem::deleteFile(*it);
+			for (auto const& path : fpset) {
+				QString fn = toQString(path.withoutParentDir());
+				if (fn.startsWith("room") || fn.startsWith("popups")) {
+					TSystem::deleteFile(path);
+				}
 			}
 		} catch (...) {
 		}
diff --git a/toonz/sources/toonz/subscenecommand.cpp b/toonz/sources/toonz/subscenecommand.cpp
index 9527fc0..bea1ebe 100644
--- a/toonz/sources/toonz/subscenecommand.cpp
+++ b/toonz/sources/toonz/subscenecommand.cpp
@@ -508,8 +508,7 @@ TFx *explodeFxSubTree(TFx *innerFx, QMap<TFx *, QPair<TFx *, int>> &fxs, FxDag *
 		TFx *root = sortedFx.begin().value();
 		QMultiMap<int, TFx *>::iterator it = sortedFx.begin();
 		outerDag->removeFromXsheet(it.value());
-		it++;
-		for (it; it != sortedFx.end(); it++) {
+		for (++it; it != sortedFx.end(); ++it) {
 			TFx *fx = it.value();
 			assert(fx);
 			TFx *overFx = TFx::create("overFx");
diff --git a/toonz/sources/toonz/vectorizerpopup.cpp b/toonz/sources/toonz/vectorizerpopup.cpp
index b7c88dd..a49635b 100644
--- a/toonz/sources/toonz/vectorizerpopup.cpp
+++ b/toonz/sources/toonz/vectorizerpopup.cpp
@@ -913,9 +913,8 @@ bool VectorizerPopup::apply()
 	assert(ret);
 
 	int newIndexColumn = c1 + 1;
-	std::set<TXshLevel *>::iterator it = levels.begin();
-	for (it; it != levels.end(); it++) {
-		TXshSimpleLevel *sl = dynamic_cast<TXshSimpleLevel *>(*it);
+	for (auto const level : levels) {
+		TXshSimpleLevel *sl = dynamic_cast<TXshSimpleLevel *>(level);
 		if (!sl || !sl->getSimpleLevel() || !isLevelToConvert(sl)) {
 			QString levelName = tr(toString(sl->getName()).c_str());
 			QString errorMsg = tr("Cannot convert to vector the current selection.") + levelName;
@@ -969,12 +968,10 @@ bool VectorizerPopup::apply()
 					TFrameId curFid = cell.getFrameId();
 					std::vector<TFrameId> newFids;
 					vl->getFids(newFids);
-					std::vector<TFrameId>::iterator it1 = newFids.begin();
-					for (it1; it1 != newFids.end(); it1++) {
-						TFrameId id = *it1;
-						if (id.getNumber() == curFid.getNumber() ||			   // Hanno stesso numero di frame
-							(id.getNumber() == 1 && curFid.getNumber() == -2)) // La vecchia cella non ha numero di frame
-							xsheet->setCell(r, newIndexColumn, TXshCell(vl, id));
+					for (auto const& fid : newFids) {
+						if (fid.getNumber() == curFid.getNumber() ||			   // Hanno stesso numero di frame
+							(fid.getNumber() == 1 && curFid.getNumber() == -2)) // La vecchia cella non ha numero di frame
+							xsheet->setCell(r, newIndexColumn, TXshCell(vl, fid));
 					}
 				}
 			}
diff --git a/toonz/sources/toonz/xsheetdragtool.cpp b/toonz/sources/toonz/xsheetdragtool.cpp
index a50357a..56a7a25 100644
--- a/toonz/sources/toonz/xsheetdragtool.cpp
+++ b/toonz/sources/toonz/xsheetdragtool.cpp
@@ -2184,9 +2184,9 @@ public:
 				return;
 			std::vector<TFrameId> fids;
 			std::set<TFrameId> fidsSet = s->getSelectedFids();
-			std::set<TFrameId>::iterator it = fidsSet.begin();
-			for (it; it != fidsSet.end(); it++)
-				fids.push_back(*it);
+			for (auto const& fid : fidsSet) {
+				fids.push_back(fid);
+			}
 			m_data->addSimpleLevel(std::make_pair(sl, fids));
 		}
 		refreshCellsArea();
diff --git a/toonz/sources/toonzlib/levelset.cpp b/toonz/sources/toonzlib/levelset.cpp
index 9658954..9578a69 100644
--- a/toonz/sources/toonzlib/levelset.cpp
+++ b/toonz/sources/toonzlib/levelset.cpp
@@ -135,8 +135,7 @@ TXshLevel *TLevelSet::getLevel(const ToonzScene &scene, const TFilePath &levelPa
 bool TLevelSet::hasLevel(const std::wstring &levelName) const
 {
 	std::vector<TXshLevel *>::const_iterator it = m_levels.begin();
-	for (it; it != m_levels.end(); it++) {
-		TXshLevel *level = *it;
+	for (auto const level : m_levels) {
 		if (levelName == level->getName())
 			return true;
 	}
diff --git a/toonz/sources/toonzlib/palettecmd.cpp b/toonz/sources/toonzlib/palettecmd.cpp
index 078623d..b43a5dd 100644
--- a/toonz/sources/toonzlib/palettecmd.cpp
+++ b/toonz/sources/toonzlib/palettecmd.cpp
@@ -155,9 +155,7 @@ bool isStyleUsed(const TImageP image, int styleId)
 /*! Return true if one style is used. */
 bool areStylesUsed(const set<TXshSimpleLevel *> levels, const std::vector<int> styleIds)
 {
-	set<TXshSimpleLevel *>::const_iterator it = levels.begin();
-	for (it; it != levels.end(); it++) {
-		TXshSimpleLevel *level = *it;
+	for (auto const level : levels) {
 		std::vector<TFrameId> fids;
 		level->getFids(fids);
 		int i;
@@ -538,9 +536,7 @@ namespace
 
 void eraseStylesInLevels(const set<TXshSimpleLevel *> &levels, const std::vector<int> styleIds)
 {
-	set<TXshSimpleLevel *>::const_iterator it = levels.begin();
-	for (it; it != levels.end(); it++) {
-		TXshSimpleLevel *level = *it;
+	for (auto const level : levels) {
 		std::vector<TFrameId> fids;
 		level->getFids(fids);
 		int i;
diff --git a/toonz/sources/toonzlib/preferences.cpp b/toonz/sources/toonzlib/preferences.cpp
index a3cf3ac..d285496 100644
--- a/toonz/sources/toonzlib/preferences.cpp
+++ b/toonz/sources/toonzlib/preferences.cpp
@@ -354,13 +354,11 @@ Preferences::Preferences()
 
 		if (langPathFs.doesExist() && langPathFs.isDirectory()) {
 			TSystem::readDirectory(lang_fpset, lang_path, true, false);
-		} else {
 		}
-		TFilePathSet::iterator it = lang_fpset.begin();
 
-		int i = 1;
-		for (it; it != lang_fpset.end(); it++, i++) {
-			TFilePath newPath = *it;
+		int i = 0;
+		for (auto const& newPath : lang_fpset) {
+			++i;
 			if (newPath == lang_path)
 				continue;
 			if (TFileStatus(newPath).isDirectory()) {
@@ -375,10 +373,9 @@ Preferences::Preferences()
 	TFilePathSet fpset;
 	try {
 		TSystem::readDirectory(fpset, path, true, false);
-		TFilePathSet::iterator it = fpset.begin();
-		int i = 0;
-		for (it; it != fpset.end(); it++, i++) {
-			TFilePath newPath = *it;
+		int i = -1;
+		for (auto const& newPath : fpset) {
+			++i;
 			if (newPath == path)
 				continue;
 			QString fpName = QString::fromStdWString(newPath.getWideName());
diff --git a/toonz/sources/toonzlib/txshsimplelevel.cpp b/toonz/sources/toonzlib/txshsimplelevel.cpp
index 1a56135..ef5bdda 100644
--- a/toonz/sources/toonzlib/txshsimplelevel.cpp
+++ b/toonz/sources/toonzlib/txshsimplelevel.cpp
@@ -1574,7 +1574,6 @@ void TXshSimpleLevel::saveSimpleLevel(const TFilePath &decodedFp, bool overwrite
 
 	std::vector<TFrameId> fids;
 	getFids(fids);
-	std::vector<TFrameId>::iterator it;
 
 	bool isLevelModified = getProperties()->getDirtyFlag();
 	bool isPaletteModified = false;
@@ -1630,11 +1629,11 @@ void TXshSimpleLevel::saveSimpleLevel(const TFilePath &decodedFp, bool overwrite
 				// is a scan-cleanup mix). This is fine even on the temporarily substituted m_path.
 				std::map<TFrameId, TFrameId> renumberTable;
 
-				std::map<TFrameId, TFrameId>::reverse_iterator mapIt = m_renumberTable.rbegin();
-				for (mapIt; mapIt != m_renumberTable.rend(); ++mapIt) {
-					TFrameId id = mapIt->first;
-					if (getFrameStatus(id) != Scanned && getFrameStatus(id) != CleanupPreview)
-						renumberTable[id] = mapIt->second;
+				for (auto it = m_renumberTable.rbegin(); it != m_renumberTable.rend(); ++it) {
+					TFrameId id = (*it).first;
+					if ((getFrameStatus(id) != Scanned) && (getFrameStatus(id) != CleanupPreview)) {
+						renumberTable[id] = (*it).second;
+					}
 				}
 
 				m_renumberTable.clear();
@@ -1649,12 +1648,12 @@ void TXshSimpleLevel::saveSimpleLevel(const TFilePath &decodedFp, bool overwrite
 
 				ImageLoader::BuildExtData extData(this, TFrameId());
 
-				for (it = fids.begin(); it != fids.end(); ++it) {
-					std::string imageId = getImageId(*it, Normal); // Retrieve the actual level frames ("L_whatever")
+				for (auto const& fid : fids) {
+					std::string imageId = getImageId(fid, Normal); // Retrieve the actual level frames ("L_whatever")
 					if (!ImageManager::instance()->isModified(imageId))
 						continue;
 
-					extData.m_fid = *it;
+					extData.m_fid = fid;
 					TImageP img = ImageManager::instance()->getImage(imageId, imFlags, &extData);
 
 					assert(img);
@@ -1678,7 +1677,7 @@ void TXshSimpleLevel::saveSimpleLevel(const TFilePath &decodedFp, bool overwrite
 						ti->setSavebox(saveBox);
 					}
 
-					lw->getFrameWriter(*it)->save(img);
+					lw->getFrameWriter(fid)->save(img);
 				}
 
 				lw = TLevelWriterP(); // TLevelWriterP's destructor saves the palette
@@ -1708,12 +1707,12 @@ void TXshSimpleLevel::saveSimpleLevel(const TFilePath &decodedFp, bool overwrite
 
 				ImageLoader::BuildExtData extData(this, TFrameId());
 
-				for (it = fids.begin(); it != fids.end(); ++it) {
-					std::string imageId = getImageId(*it, Normal); // Retrieve the actual level frames ("L_whatever")
+				for (auto const& fid : fids) {
+					std::string imageId = getImageId(fid, Normal); // Retrieve the actual level frames ("L_whatever")
 					if (!ImageManager::instance()->isModified(imageId))
 						continue;
 
-					extData.m_fid = *it;
+					extData.m_fid = fid;
 					TImageP img = ImageManager::instance()->getImage(imageId, imFlags, &extData);
 
 					assert(img);
@@ -1730,7 +1729,7 @@ void TXshSimpleLevel::saveSimpleLevel(const TFilePath &decodedFp, bool overwrite
 					if (subs != 1)
 						continue;
 
-					updater.update(*it, img);
+					updater.update(fid, img);
 				}
 			}
 			updater.close(); //Needs the original level subs
@@ -2006,16 +2005,16 @@ void TXshSimpleLevel::renumber(const std::vector<TFrameId> &fids)
 		TFrameId oldFrameId = *it;
 		TFrameId newFrameId = fids[i++];
 		table[oldFrameId] = newFrameId;
-		std::map<TFrameId, TFrameId>::iterator mapIt = m_renumberTable.begin();
-		for (mapIt; mapIt != m_renumberTable.end(); ++mapIt)
-			if (mapIt->second == oldFrameId) {
-				newRenumberTable[mapIt->first] = newFrameId;
+		for (auto const& renumber : m_renumberTable) {
+			if (renumber.second == oldFrameId) {
+				newRenumberTable[renumber.first] = newFrameId;
 				break;
 			}
+		}
+	}
+	for (auto const& renumber : newRenumberTable) {
+		m_renumberTable[renumber.first] = renumber.second;
 	}
-	std::map<TFrameId, TFrameId>::iterator newMapIt = newRenumberTable.begin();
-	for (newMapIt; newMapIt != newRenumberTable.end(); ++newMapIt)
-		m_renumberTable[newMapIt->first] = newMapIt->second;
 
 	m_frames.clear();
 	for (i = 0; i < n; ++i) {
diff --git a/toonz/sources/toonzlib/txshsoundtextcolumn.cpp b/toonz/sources/toonzlib/txshsoundtextcolumn.cpp
index 4324fb8..170d9db 100644
--- a/toonz/sources/toonzlib/txshsoundtextcolumn.cpp
+++ b/toonz/sources/toonzlib/txshsoundtextcolumn.cpp
@@ -30,9 +30,8 @@ void TXshSoundTextColumn::createSoundTextLevel(int row, QList<QString> textList)
 {
 	TXshSoundTextLevel *level = new TXshSoundTextLevel();
 	level->setType(SND_TXT_XSHLEVEL);
-	int i = 0;
 	TXshCell cell;
-	for (i; i < textList.size(); i++, row++) {
+	for (int i = 0; i < textList.size(); i++, row++) {
 		QString str = textList.at(i);
 		QString precStr = (i > 0) ? level->getFrameText(i - 1) : QString();
 		if (str == QString("<none>")) {
diff --git a/toonz/sources/toonzqt/fxschematicscene.cpp b/toonz/sources/toonzqt/fxschematicscene.cpp
index af9c9c4..1693839 100644
--- a/toonz/sources/toonzqt/fxschematicscene.cpp
+++ b/toonz/sources/toonzqt/fxschematicscene.cpp
@@ -980,8 +980,7 @@ QPointF FxSchematicScene::nearestPoint(const QPointF &point)
 FxSchematicNode *FxSchematicScene::getFxNodeFromPosition(const QPointF &pos)
 {
 	QList<QGraphicsItem *> pickedItems = items(pos);
-	int i = 0;
-	for (i; i < pickedItems.size(); i++) {
+	for (int i = 0; i < pickedItems.size(); i++) {
 		FxSchematicNode *fxNode = dynamic_cast<FxSchematicNode *>(pickedItems.at(i));
 		if (fxNode)
 			return fxNode;
@@ -1057,9 +1056,8 @@ QGraphicsItem *FxSchematicScene::getCurrentNode()
 {
 	QList<QGraphicsItem *> allItems = items();
 
-	QList<QGraphicsItem *>::iterator it = allItems.begin();
-	for (it; it != allItems.end(); it++) {
-		FxSchematicNode *node = dynamic_cast<FxSchematicNode *>(*it);
+	for (auto const item : allItems) {
+		FxSchematicNode *node = dynamic_cast<FxSchematicNode *>(item);
 		if (node && node->getFx() == m_fxHandle->getFx())
 			return node;
 	}
diff --git a/toonz/sources/toonzqt/schematicnode.cpp b/toonz/sources/toonzqt/schematicnode.cpp
index 5406573..62179de 100644
--- a/toonz/sources/toonzqt/schematicnode.cpp
+++ b/toonz/sources/toonzqt/schematicnode.cpp
@@ -849,12 +849,10 @@ void SchematicNode::mouseMoveEvent(QGraphicsSceneMouseEvent *me)
 	QList<QGraphicsItem *> items = scene()->selectedItems();
 	if (items.empty())
 		return;
-	QList<QGraphicsItem *>::iterator it = items.begin();
 	QPointF delta = me->scenePos() - me->lastScenePos();
 	QGraphicsView *viewer = scene()->views()[0];
-	it = items.begin();
-	for (it; it != items.end(); it++) {
-		SchematicNode *node = dynamic_cast<SchematicNode *>(*it);
+	for (auto const& item : items) {
+		SchematicNode *node = dynamic_cast<SchematicNode *>(item);
 		if (node) {
 			node->setPosition(node->scenePos() + delta);
 			node->setSchematicNodePos(node->scenePos());
diff --git a/toonz/sources/toonzqt/schematicviewer.cpp b/toonz/sources/toonzqt/schematicviewer.cpp
index 8fd0fd0..51d7c75 100644
--- a/toonz/sources/toonzqt/schematicviewer.cpp
+++ b/toonz/sources/toonzqt/schematicviewer.cpp
@@ -159,15 +159,14 @@ void SchematicScene::clearAllItems()
 bool SchematicScene::isAnEmptyZone(const QRectF &rect)
 {
 	QList<QGraphicsItem *> allItems = items();
-	QList<QGraphicsItem *>::iterator it = allItems.begin();
-	for (it; it != allItems.end(); it++) {
-		SchematicNode *node = dynamic_cast<SchematicNode *>(*it);
+	for (auto const level : allItems) {
+		SchematicNode *node = dynamic_cast<SchematicNode *>(level);
 		if (!node)
 			continue;
 		FxSchematicNode *fxNode = dynamic_cast<FxSchematicNode *>(node);
 		if (fxNode && fxNode->isA(eXSheetFx))
 			continue;
-		if ((*it)->boundingRect().translated((*it)->scenePos()).intersects(rect))
+		if (node->boundingRect().translated(node->scenePos()).intersects(rect))
 			return false;
 	}
 	return true;
@@ -179,10 +178,9 @@ QVector<SchematicNode *> SchematicScene::getPlacedNode(SchematicNode *node)
 {
 	QRectF rect = node->boundingRect().translated(node->scenePos());
 	QList<QGraphicsItem *> allItems = items();
-	QList<QGraphicsItem *>::iterator it = allItems.begin();
 	QVector<SchematicNode *> nodes;
-	for (it; it != allItems.end(); it++) {
-		SchematicNode *placedNode = dynamic_cast<SchematicNode *>(*it);
+	for (auto const item : allItems) {
+		SchematicNode *placedNode = dynamic_cast<SchematicNode *>(item);
 		if (!placedNode || placedNode == node)
 			continue;
 		QRectF nodeRect = placedNode->boundingRect().translated(placedNode->scenePos());
diff --git a/toonz/sources/toonzqt/stageschematicscene.cpp b/toonz/sources/toonzqt/stageschematicscene.cpp
index 908d3cc..bf4dd90 100644
--- a/toonz/sources/toonzqt/stageschematicscene.cpp
+++ b/toonz/sources/toonzqt/stageschematicscene.cpp
@@ -649,9 +649,8 @@ QGraphicsItem *StageSchematicScene::getCurrentNode()
 {
 	QList<QGraphicsItem *> allItems = items();
 
-	QList<QGraphicsItem *>::iterator it = allItems.begin();
-	for (it; it != allItems.end(); it++) {
-		StageSchematicNode *node = dynamic_cast<StageSchematicNode *>(*it);
+	for (auto const item : allItems) {
+		StageSchematicNode *node = dynamic_cast<StageSchematicNode *>(item);
 		if (node && node->getStageObject()->getId() == m_objHandle->getObjectId())
 			return node;
 	}
@@ -1188,8 +1187,7 @@ void StageSchematicScene::mousePressEvent(QGraphicsSceneMouseEvent *me)
 SchematicNode *StageSchematicScene::getNodeFromPosition(const QPointF &pos)
 {
 	QList<QGraphicsItem *> pickedItems = items(pos);
-	int i = 0;
-	for (i; i < pickedItems.size(); i++) {
+	for (int i = 0; i < pickedItems.size(); i++) {
 		SchematicNode *node = dynamic_cast<SchematicNode *>(pickedItems.at(i));
 		if (node)
 			return node;
diff --git a/toonz/sources/toonzqt/styleselection.cpp b/toonz/sources/toonzqt/styleselection.cpp
index b7d78df..5e3f593 100644
--- a/toonz/sources/toonzqt/styleselection.cpp
+++ b/toonz/sources/toonzqt/styleselection.cpp
@@ -765,9 +765,7 @@ void TStyleSelection::eraseUnsedStyle()
 	//Verifico quali stili sono usati e quali no
 	std::map<int, bool> usedStyleIds;
 	int pageCount = palette->getPageCount();
-	std::set<TXshSimpleLevel *>::const_iterator it = levels.begin();
-	for (it; it != levels.end(); it++) {
-		TXshSimpleLevel *level = *it;
+	for (auto const level : levels) {
 		std::vector<TFrameId> fids;
 		level->getFids(fids);
 		int m, i, j;