Fix else ifs

Makefile

@@ -4,13 +4,13 @@ parser.cpp parser.hpp: parser.y
 	bison -d -o parser.cpp parser.y
 
 tree.o: tree.cpp
-	g++ -g -c -o tree.o tree.cpp
+	g++ -std=c++11 -g -c -o tree.o tree.cpp
 
 scanner.cpp: scanner.l
 	flex -o scanner.cpp scanner.l
 
 parse: main.cpp parser.cpp scanner.cpp tree.o
-	g++ -g main.cpp parser.cpp scanner.cpp tree.o -o parse
+	g++ -std=c++11 -g main.cpp parser.cpp scanner.cpp tree.o -o parse
 
 clean:
 	rm -f parse scanner.cpp parser.cpp parser.hpp tree.o