/in/foo.c: In function 'main':
/in/foo.c:6:9: error: 'delta' undeclared (first use in this function)
    6 |         delta=b*b-4*a*c;
      |         ^~~~~
/in/foo.c:6:9: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:8:17: error: 'x' undeclared (first use in this function)
    8 |                 x=-c/b;
      |                 ^
/in/foo.c:13:25: error: 'x1' undeclared (first use in this function)
   13 |                         x1=(-b+sqrt(delta))/(2*a);
      |                         ^~
/in/foo.c:14:25: error: 'x2' undeclared (first use in this function)
   14 |                         x2=(-b-sqrt(delta))/(2*a);
      |                         ^~
/in/foo.c:22:25: error: 'real' undeclared (first use in this function)
   22 |                         real=-b/(2*a);
      |                         ^~~~
/in/foo.c:23:25: error: 'imag' undeclared (first use in this function)
   23 |                         imag=sqrt(-delta)/(2*a);
      |                         ^~~~