foo.c: In function 'main':
foo.c:7:2: warning: 'gets' is deprecated [-Wdeprecated-declarations]
  gets(str);
  ^~~~
In file included from /usr/include/stdio.h:862:0,
                 from foo.c:1:
/usr/include/x86_64-linux-gnu/bits/stdio2.h:232:1: note: declared here
 gets (char *__str)
 ^~~~
foo.c:8:2: warning: implicit declaration of function 'scanf_s'; did you mean 'scanf'? [-Wimplicit-function-declaration]
  scanf_s("%d", &k);
  ^~~~~~~
  scanf
foo.c:7:2: warning: ignoring return value of 'gets', declared with attribute warn_unused_result [-Wunused-result]
  gets(str);
  ^~~~~~~~~
/tmp/cc0alcB1.o: In function `main':
foo.c:(.text.startup+0x23): warning: the `gets' function is dangerous and should not be used.
foo.c:(.text.startup+0x36): undefined reference to `scanf_s'
collect2: error: ld returned 1 exit status

[Hydro](https://hydro.ac)提供评测服务