--- tree.hh-3.18/src/Makefile
+++ tree.hh-3.18/src/Makefile
@@ -2,19 +2,19 @@
 all: test1 test2 test_tree
 
 %.o: %.cc tree.hh
-	g++ -g -c -o $@ -Wall -O2 -std=c++11 -I. $<
+	$(CXX) -g -c -o $@ -Wall -O2 -std=c++11 -I. $<
 
 test1: test1.o 
-	g++ -o test1 test1.o
+	$(CXX) -o test1 test1.o
 
 test2: test2.o 
-	g++ -o test2 test2.o
+	$(CXX) -o test2 test2.o
 
 test_tree: test_tree.o
-	g++ -o test_tree test_tree.o
+	$(CXX) -o test_tree test_tree.o
 
 sample_path: sample_path.o
-	g++ -o sample_path sample_path.o
+	$(CXX) -o sample_path sample_path.o
 
 run_tests: test1 test1.req
 	./test1 > test1.res