/in/foo.cc: In function 'void ruler()':
/in/foo.cc:21:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int j=0;j<prime.size()&&prime[j]*i<N;++j){
                     ~^~~~~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:36:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<prime.size();++i){
                 ~^~~~~~~~~~~~~
/in/foo.cc:44:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<prime.size();++i){
                 ~^~~~~~~~~~~~~
/in/foo.cc:52:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<prime.size();++i){
                 ~^~~~~~~~~~~~~
/in/foo.cc:60:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<prime.size();++i){
                 ~^~~~~~~~~~~~~