foo.cc: In function 'int main()':
foo.cc:6:23: warning: unused variable 'b' [-Wunused-variable]
  long long x,x1,x2,x3,b;
                       ^
foo.cc: In function 'int op(int, int, int)':
foo.cc:37:1: warning: no return statement in function returning non-void [-Wreturn-type]
 }
 ^