/in/foo.c:1:9: error: expected '=', ',', ';', 'asm' or '__attribute__' before '<' token
    1 | include <stdio.h>
      |         ^
/in/foo.c: In function 'main':
/in/foo.c:9:5: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
    9 |     scanf("%f,%f,%f", &a, &b, &c);
      |     ^~~~~
/in/foo.c:3:1: note: include '<stdio.h>' or provide a declaration of 'scanf'
    2 | #include <math.h>
  +++ |+#include <stdio.h>
    3 | 
/in/foo.c:9:5: warning: incompatible implicit declaration of built-in function 'scanf' [-Wbuiltin-declaration-mismatch]
    9 |     scanf("%f,%f,%f", &a, &b, &c);
      |     ^~~~~
/in/foo.c:9:5: note: include '<stdio.h>' or provide a declaration of 'scanf'
/in/foo.c:15:9: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
   15 |         printf("%.2f\n", x1)；
      |         ^~~~~~
/in/foo.c:15:9: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c:15:9: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
/in/foo.c:15:9: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c:15:29: error: expected ';' before '\U0000ff1b'
   15 |         printf("%.2f\n", x1)；
      |                             ^~
      |                             ;
/in/foo.c:25:13: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   25 |             printf("%.2f\n", x1);
      |             ^~~~~~
/in/foo.c:25:13: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c:31:13: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   31 |             printf("%.2f\n", x1);
      |             ^~~~~~
/in/foo.c:31:13: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c:35:13: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
   35 |             printf("无实数解\n");
      |             ^~~~~~
/in/foo.c:35:13: note: include '<stdio.h>' or provide a declaration of 'printf'