foo.cc: In function 'int main()':
foo.cc:11:2: warning: statement has no effect [-Wunused-value]
  (int) a;
  ^~~~~~~
foo.cc:12:2: warning: statement has no effect [-Wunused-value]
  (int) b;
  ^~~~~~~
foo.cc:19:7: warning: unused variable 's' [-Wunused-variable]
   int s;
       ^