foo.c: In function ‘main’:
foo.c:23:9: warning: implicit declaration of function ‘scanf’ [-Wimplicit-function-declaration]
   23 |         scanf("%d", &b);
      |         ^~~~~
foo.c:1:1: note: include ‘<stdio.h>’ or provide a declaration of ‘scanf’
  +++ |+#include <stdio.h>
    1 | int huiwen(int number)
foo.c:23:9: warning: incompatible implicit declaration of built-in function ‘scanf’ [-Wbuiltin-declaration-mismatch]
   23 |         scanf("%d", &b);
      |         ^~~~~
foo.c:23:9: note: include ‘<stdio.h>’ or provide a declaration of ‘scanf’
foo.c:26:17: warning: implicit declaration of function ‘printf’ [-Wimplicit-function-declaration]
   26 |                 printf("Yes\n");
      |                 ^~~~~~
foo.c:26:17: note: include ‘<stdio.h>’ or provide a declaration of ‘printf’
foo.c:26:17: warning: incompatible implicit declaration of built-in function ‘printf’ [-Wbuiltin-declaration-mismatch]
foo.c:26:17: note: include ‘<stdio.h>’ or provide a declaration of ‘printf’
foo.c:30:17: warning: incompatible implicit declaration of built-in function ‘printf’ [-Wbuiltin-declaration-mismatch]
   30 |                 printf("No\n");
      |                 ^~~~~~
foo.c:30:17: note: include ‘<stdio.h>’ or provide a declaration of ‘printf’