/in/foo.cc: In function 'void fangcheng()':
/in/foo.cc:123:30: warning: 'f.fangcheng::c' may be used uninitialized in this function [-Wmaybe-uninitialized]
         if (a == 0 && b == 0 && c == 0)
             ~~~~~~~~~~~~~~~~~^~~~~~~~~
/in/foo.cc:161:22: note: 'f.fangcheng::c' was declared here
     struct fangcheng f(s);
                      ^
/in/foo.cc:134:56: warning: 'f.fangcheng::b' may be used uninitialized in this function [-Wmaybe-uninitialized]
             cout << fixed << setprecision(5) << n(-c / (float)b);
                                                        ^~~~~~~~
/in/foo.cc:161:22: note: 'f.fangcheng::b' was declared here
     struct fangcheng f(s);
                      ^
/in/foo.cc:139:66: warning: 'f.fangcheng::a' may be used uninitialized in this function [-Wmaybe-uninitialized]
             cout << fixed << setprecision(5) << n(-b / (float)(2 * a));
                                                               ~~~^~~~
/in/foo.cc:161:22: note: 'f.fangcheng::a' was declared here
     struct fangcheng f(s);
                      ^