foo.cc: In function 'int main()':
foo.cc:5:8: warning: unused variable 'a1' [-Wunused-variable]
  int n,a1,a2,a3=1,a4=0;
        ^~
foo.cc:5:11: warning: unused variable 'a2' [-Wunused-variable]
  int n,a1,a2,a3=1,a4=0;
           ^~
foo.cc:5:14: warning: unused variable 'a3' [-Wunused-variable]
  int n,a1,a2,a3=1,a4=0;
              ^~