/in/foo.cc: In function 'int main()':
/in/foo.cc:14:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         if (a>=n/2)
             ~^~~~~
/in/foo.cc:12:10: warning: 'a' may be used uninitialized in this function [-Wmaybe-uninitialized]
         a=a*2;
         ~^~~~