You need another rule to build the binaries:
$(BINDIR)/%: $(OBJDIR)/%.o
$(CC) -o $@ $< $(CFLAGS) # you don't actually need that line!
And then one shortcut rule:
TARGETS=$(patsubst $(SRCDIR)/%.cpp,%,$(wildcard $(SRCDIR)/*.cpp))
$(TARGETS): %: $(BINDIR)/%
.PHONY: $(TARGETS)
Which allows you to say make 1
instead of make bin/1
.