Update makefile build location

makefile

@@ -2,11 +2,13 @@
 CC = g++
 
 TARGET = checkbit
+BUILDIR = build
 
 all: $(TARGET)
 
 $(TARGET): $(TARGET).cpp
-	$(CC) -o $(TARGET) $(TARGET).cpp
+	mkdir $(BUILDIR)
+	$(CC) -o $(BUILDIR)/$(TARGET) $(TARGET).cpp
 
 clean:
 	$(RM) $(TARGET)