/in/foo.cc: In function 'void output(int, int)':
/in/foo.cc:12:19: warning: left operand of comma operator has no effect [-Wunused-value]
                 l == 0, r == 0;
                 ~~^~~~
/in/foo.cc:12:27: warning: right operand of comma operator has no effect [-Wunused-value]
                 l == 0, r == 0;
                         ~~^~~~