/in/foo.c: In function 'main':
/in/foo.c:18:20: warning: format '%f' expects a matching 'double' argument [-Wformat=]
   printf("%.2f\n%.2f",x1);
                    ^
/in/foo.c:28:23: warning: 'i' may be used uninitialized in this function [-Wmaybe-uninitialized]
   x1=(-b+sqrt(-delta))*i/(2*a);
      ~~~~~~~~~~~~~~~~~^~