/in/foo.c: In function 'qiujie':
/in/foo.c:6:17: error: 'x' undeclared (first use in this function)
    6 |                 x=-c/b;
      |                 ^
/in/foo.c:6:17: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:10:17: error: 'delta' undeclared (first use in this function)
   10 |                 delta=b*b-4*a*c;
      |                 ^~~~~
/in/foo.c:16:25: error: 'x1' undeclared (first use in this function)
   16 |                         x1=(-b+sqrt(delta))/(2*a);
      |                         ^~
/in/foo.c:17:25: error: 'x2' undeclared (first use in this function)
   17 |                         x2=(-b-sqrt(delta))/(2*a);
      |                         ^~
/in/foo.c:21:25: error: 'realpart' undeclared (first use in this function)
   21 |                         realpart=-b/(2*a);
      |                         ^~~~~~~~
/in/foo.c:22:25: error: 'imagpart' undeclared (first use in this function)
   22 |                         imagpart=sqrt(-delta)/(2*a);
      |                         ^~~~~~~~