foo.c: In function ‘main’:
foo.c:13:9: warning: implicit declaration of function ‘scanf’ [-Wimplicit-function-declaration]
   13 |         scanf("%d %d",  & a, &b);
      |         ^~~~~
foo.c:1:1: note: include ‘<stdio.h>’ or provide a declaration of ‘scanf’
  +++ |+#include <stdio.h>
    1 | int fbnq(int n)
foo.c:13:9: warning: incompatible implicit declaration of built-in function ‘scanf’ [-Wbuiltin-declaration-mismatch]
   13 |         scanf("%d %d",  & a, &b);
      |         ^~~~~
foo.c:13:9: note: include ‘<stdio.h>’ or provide a declaration of ‘scanf’
foo.c:18:9: warning: implicit declaration of function ‘printf’ [-Wimplicit-function-declaration]
   18 |         printf("%d\n", sum);
      |         ^~~~~~
foo.c:18:9: note: include ‘<stdio.h>’ or provide a declaration of ‘printf’
foo.c:18:9: warning: incompatible implicit declaration of built-in function ‘printf’ [-Wbuiltin-declaration-mismatch]
foo.c:18:9: note: include ‘<stdio.h>’ or provide a declaration of ‘printf’