/in/foo.cc: In function 'int main()':
/in/foo.cc:7:22: warning: variable 'a3' set but not used [-Wunused-but-set-variable]
    7 |         double a1,a2,a3;
      |                      ^~
In file included from /usr/include/c++/12/istream:39,
                 from /usr/include/c++/12/sstream:38,
                 from /usr/include/c++/12/complex:45,
                 from /usr/include/c++/12/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/12/bits/stdc++.h:54,
                 from /in/foo.cc:1:
In member function 'std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(double) [with _CharT = char; _Traits = std::char_traits<char>]',
    inlined from 'int main()' at /in/foo.cc:21:33:
/usr/include/c++/12/ostream:221:25: warning: 'a1' may be used uninitialized [-Wmaybe-uninitialized]
  221 |       { return _M_insert(__f); }
      |                ~~~~~~~~~^~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:7:16: note: 'a1' was declared here
    7 |         double a1,a2,a3;
      |                ^~