/in/foo.cc: In function 'void init2()':
/in/foo.cc:27:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int j=0;j<prime_factor[i].size();++j)
                     ~^~~~~~~~~~~~~~~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:49:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int i=0;i<prime_factor[j].size();i++)
                     ~^~~~~~~~~~~~~~~~~~~~~~~