/in/foo.c: In function 'main':
/in/foo.c:9:5: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
    9 |     scanf("%lf,%lf,%lf", &a, &b, &c);
      |     ^~~~~
/in/foo.c:6:1: note: include '<stdio.h>' or provide a declaration of 'scanf'
    5 | #include <math.h>
  +++ |+#include <stdio.h>
    6 | 
/in/foo.c:9:5: warning: incompatible implicit declaration of built-in function 'scanf' [-Wbuiltin-declaration-mismatch]
    9 |     scanf("%lf,%lf,%lf", &a, &b, &c);
      |     ^~~~~
/in/foo.c:9:5: note: include '<stdio.h>' or provide a declaration of 'scanf'
/in/foo.c:13:9: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
   13 |         printf("%.2f\n", -c / b);
      |         ^~~~~~
/in/foo.c:13:9: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c:13:9: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
/in/foo.c:13:9: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c:19:13: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   19 |             printf("%.2f\n%.2f\n", x1, x2);
      |             ^~~~~~
/in/foo.c:19:13: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c:22:13: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   22 |             printf("%.2f\n", x);
      |             ^~~~~~
/in/foo.c:22:13: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c:28:17: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   28 |                 printf("%.2f+%.2fi\n%.2f-%.2fi\n", real, imag, real, imag);
      |                 ^~~~~~
/in/foo.c:28:17: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c:30:17: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   30 |                 printf("%.2f%.2fi\n%.2f+%.2fi\n", real, imag, real, -imag);
      |                 ^~~~~~
/in/foo.c:30:17: note: include '<stdio.h>' or provide a declaration of 'printf'