foo.c: In function 'main':
foo.c:9:5: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
    9 |     scanf("%d ",&n);
      |     ^~~~~
foo.c:1:1: note: include '<stdio.h>' or provide a declaration of 'scanf'
  +++ |+#include <stdio.h>
    1 | int main()
foo.c:9:5: warning: incompatible implicit declaration of built-in function 'scanf' [-Wbuiltin-declaration-mismatch]
    9 |     scanf("%d ",&n);
      |     ^~~~~
foo.c:9:5: note: include '<stdio.h>' or provide a declaration of 'scanf'
foo.c:11:5: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
   11 |     printf("\n");
      |     ^~~~~~
foo.c:11:5: note: include '<stdio.h>' or provide a declaration of 'printf'
foo.c:11:5: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
foo.c:11:5: note: include '<stdio.h>' or provide a declaration of 'printf'
foo.c:33:26: warning: format '%d' expects argument of type 'int', but argument 2 has type 'int *' [-Wformat=]
   33 |                 printf("%d",&c);
      |                         ~^  ~~
      |                          |  |
      |                          |  int *
      |                          int
      |                         %ls

[Hydro](https://hydro.ac)提供评测服务