/in/foo.cc: In function 'int main()':
/in/foo.cc:20:16: warning: right operand of comma operator has no effect [-Wunused-value]
  for (i = 1, i <= len; i++)
              ~~^~~~~~
/in/foo.cc:20:27: error: expected ';' before ')' token
  for (i = 1, i <= len; i++)
                           ^