/in/foo.cc: In function 'int main()':
/in/foo.cc:27:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(i=0;i<formula.size();i++)
             ~^~~~~~~~~~~~~~~
/in/foo.cc:41:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(i=0;i<oprtr_pos.size()-1;i++)
             ~^~~~~~~~~~~~~~~~~~~
/in/foo.cc:46:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(i=0;i<mul_pos.size();i++)
             ~^~~~~~~~~~~~~~~
/in/foo.cc:53:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(i=0;i<value.size();i++)
             ~^~~~~~~~~~~~~