foo.cc: In function ‘int main()’:
foo.cc:28:17: warning: unused variable ‘j’ [-Wunused-variable]
   28 |         int n,i,j,a;
      |                 ^
foo.cc:28:19: warning: unused variable ‘a’ [-Wunused-variable]
   28 |         int n,i,j,a;
      |                   ^