/in/foo.cc: In function 'int main()':
/in/foo.cc:4:30: warning: unused variable 'h' [-Wunused-variable]
     int  head1,back2,i,n,k,j,h;
                              ^
/in/foo.cc:5:10: warning: unused variable 'head' [-Wunused-variable]
     char head,back,a[50];
          ^~~~