some optimization

Makefile

@@ -1,5 +1,12 @@
 CXX=g++
-CXXFLAGS=-Wall -l ssl -l crypto -I src/libs -I src/auth -I src/security -I src/users -I src
+CXXFLAGS=-Wall \
+	-l ssl \
+	-l crypto \
+	-I src/libs \
+	-I src/auth \
+	-I src/security \
+	-I src/users \
+	-I src
 SOURCES=src/auth_service.cpp \
 	src/auth/auth.cpp \
 	src/auth/verify_auth.cpp \
@@ -12,16 +19,18 @@ SOURCES=src/auth_service.cpp \
 	src/users/get_all_users.cpp \
 	src/users/get_user.cpp \
 	src/AuthService/AuthService.cpp
-TARGET=build/auth_service
+TARGET=auth_service
+BUILD_DIR=build
+
 default: all
 all: build
 .PHONY: build
 build:
-	@if [ ! -d build ]; then \
-		mkdir build; \
+	@if [ ! -d $(BUILD_DIR) ]; then \
+		mkdir $(BUILD_DIR); \
 	fi
-	$(CXX) -o $(TARGET) $(SOURCES) $(CXXFLAGS)
+	$(CXX) -o $(BUILD_DIR)/$(TARGET) $(SOURCES) $(CXXFLAGS)
 clean:
-	@if [ -f $(TARGET) ]; then \
-		rm -v $(TARGET); \
+	@if [ -d $(BUILD_DIR) ]; then \
+		rm -rv $(BUILD_DIR); \
 	fi