diff --git a/src/environment.cpp b/src/environment.cpp
index d334d20..8d0656b 100644
--- a/src/environment.cpp
+++ b/src/environment.cpp
@@ -25,22 +25,22 @@ namespace envlibcpp {
         name = newName;
     }
 
-    void Environment::addEntity(Entity &entity) {
+    void Environment::addEntity(Entity& entity) {
         entity.setEnvironmentId(id);
         grid.addEntity(entity);
     }
 
-    void Environment::addEntityToLocation(Entity &entity, Location &location) {
+    void Environment::addEntityToLocation(Entity& entity, Location& location) {
         entity.setEnvironmentId(id);
         grid.addEntityToLocation(entity, location);
     }
 
-    void Environment::removeEntity(Entity &entity) {
+    void Environment::removeEntity(Entity& entity) {
         entity.setEnvironmentId(-1);
         grid.removeEntity(entity);
     }
 
-    bool Environment::isEntityPresent(Entity &entity) {
+    bool Environment::isEntityPresent(Entity& entity) {
         return grid.isEntityPresent(entity);
     }
 
@@ -54,7 +54,7 @@ namespace envlibcpp {
     }
 
     envlibcpp::Entity& Environment::getFirstEntity() {
-        for (envlibcpp::Location &location : getGrid().getLocations()) {
+        for (envlibcpp::Location& location : getGrid().getLocations()) {
             if (location.getNumEntities() > 0) {
                 return location.getEntities()[0];
             }
@@ -63,8 +63,8 @@ namespace envlibcpp {
     }
 
     envlibcpp::Entity& Environment::getEntity(int entityId) {
-        for (envlibcpp::Location &location : getGrid().getLocations()) {
-            for (envlibcpp::Entity &entity : location.getEntities()) {
+        for (envlibcpp::Location& location : getGrid().getLocations()) {
+            for (envlibcpp::Entity& entity : location.getEntities()) {
                 if (entity.getId() == entityId) {
                     return entity;
                 }
diff --git a/src/grid.cpp b/src/grid.cpp
index e68fb0f..6d0692f 100644
--- a/src/grid.cpp
+++ b/src/grid.cpp
@@ -54,11 +54,11 @@ namespace envlibcpp {
         size = newSize;
     }
 
-    void Grid::addLocation(Location &location) {
+    void Grid::addLocation(Location& location) {
         locations.push_back(location);
     }
 
-    void Grid::removeLocation(Location &location) {
+    void Grid::removeLocation(Location& location) {
         for (auto i = locations.begin(); i != locations.end(); i++) {
             if (i->getId() == location.getId()) {
                 locations.erase(i);
@@ -66,13 +66,13 @@ namespace envlibcpp {
         }
     }
 
-    void Grid::addEntity(Entity &entity) {
+    void Grid::addEntity(Entity& entity) {
         entity.setGridId(id);
-        Location &firstLocation = getRandomLocation();
+        Location& firstLocation = getRandomLocation();
         firstLocation.addEntity(entity);
     }
 
-    void Grid::addEntityToLocation(Entity &entity, Location &location) {
+    void Grid::addEntityToLocation(Entity& entity, Location& location) {
         for (Location &l : locations) {
             if (l.getId() == location.getId()) {
                 location.addEntity(entity);
@@ -80,8 +80,8 @@ namespace envlibcpp {
         }
     }
 
-    void Grid::removeEntity(Entity &entity) {
-        for (Location &location : locations) {
+    void Grid::removeEntity(Entity& entity) {
+        for (Location& location : locations) {
             if (location.isEntityPresent(entity)) {
                 location.removeEntity(entity);
                 entity.setLocationId(-1);
@@ -90,8 +90,8 @@ namespace envlibcpp {
         entity.setGridId(-1);
     }
 
-    bool Grid::isEntityPresent(Entity &entity) {
-        for (Location &location : locations) {
+    bool Grid::isEntityPresent(Entity& entity) {
+        for (Location& location : locations) {
             if (location.isEntityPresent(entity)) {
                 return true;
             }
@@ -100,7 +100,7 @@ namespace envlibcpp {
     }
 
     Location& Grid::getLocation(int locationId) {
-        for (Location &location : locations) {
+        for (Location& location : locations) {
             if (location.getId() == locationId) {
                 return location;
             }
diff --git a/src/header/environment.h b/src/header/environment.h
index fee1be4..c9fcbb3 100644
--- a/src/header/environment.h
+++ b/src/header/environment.h
@@ -16,10 +16,10 @@ namespace envlibcpp {
             std::string getName();
             Grid& getGrid();
             void setName(std::string newName);
-            void addEntity(Entity &entity);
-            void addEntityToLocation(Entity &entity, Location &location);
-            void removeEntity(Entity &entity);
-            bool isEntityPresent(Entity &entity);
+            void addEntity(Entity& entity);
+            void addEntityToLocation(Entity& entity, Location& location);
+            void removeEntity(Entity& entity);
+            bool isEntityPresent(Entity& entity);
             int getNumEntities();
             void printInfo();
             envlibcpp::Entity& getFirstEntity();
diff --git a/src/header/grid.h b/src/header/grid.h
index c369862..23e44fe 100644
--- a/src/header/grid.h
+++ b/src/header/grid.h
@@ -22,12 +22,12 @@ namespace envlibcpp {
             int getNumEntities();
             void setId(int newId);
             void setSize(int newSize);
-            void addLocation(Location &location);
-            void removeLocation(Location &location);
-            void addEntity(Entity &entity);
-            void addEntityToLocation(Entity &entity, Location &location);
-            void removeEntity(Entity &entity);
-            bool isEntityPresent(Entity &entity);
+            void addLocation(Location& location);
+            void removeLocation(Location& location);
+            void addEntity(Entity& entity);
+            void addEntityToLocation(Entity& entity, Location& location);
+            void removeEntity(Entity& entity);
+            bool isEntityPresent(Entity& entity);
             Location& getLocation(int locationId);
             Location& getRandomLocation();
         private:
diff --git a/src/location.cpp b/src/location.cpp
index 7e0f779..a38b65f 100644
--- a/src/location.cpp
+++ b/src/location.cpp
@@ -25,12 +25,12 @@ namespace envlibcpp {
         return entities.size();
     }
     
-    void Location::addEntity(Entity &entity) {
+    void Location::addEntity(Entity& entity) {
         entity.setLocationId(getId());
         entities.push_back(entity);
     }
     
-    void Location::removeEntity(Entity &entity) {
+    void Location::removeEntity(Entity& entity) {
         int index = -1;
         for (int i = 0; i < getNumEntities(); i++) {
             if (entities[i].getId() == entity.getId()) {
@@ -44,7 +44,7 @@ namespace envlibcpp {
         entity.setLocationId(-1);
     }
     
-    bool Location::isEntityPresent(Entity &entity) {
+    bool Location::isEntityPresent(Entity& entity) {
         for (Entity &e : entities) {
             if (e.getId() == entity.getId()) {
                 return true;