/in/foo.cc:8:1: warning: multi-line comment [-Wcomment]
 //          / \\|||   :   |||// \
 ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:46:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < b.size(); i++)
                  ~~^~~~~~~~~~
/in/foo.cc:49:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (j = 0; j < a.size(); j++)
               ~~^~~~~~~~~~
/in/foo.cc:57:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if (j == a.size())
       ~~^~~~~~~~~~~
/in/foo.cc:60:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < a.size(); i++)
                  ~~^~~~~~~~~~