/in/foo.cc:36:10: warning: multi-character character constant [-Wmultichar]
    cout<<'w('<<a<<','<<b<<','<<c<<')='<<dfs(a,b,c)<<endl;
          ^~~~
/in/foo.cc:36:35: warning: multi-character character constant [-Wmultichar]
    cout<<'w('<<a<<','<<b<<','<<c<<')='<<dfs(a,b,c)<<endl;
                                   ^~~~