foo.c: In function 'main':
foo.c:7:2: warning: 'gets' is deprecated [-Wdeprecated-declarations]
  gets(a);
  ^~~~
In file included from foo.c:1:0:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
foo.c:8:2: warning: 'gets' is deprecated [-Wdeprecated-declarations]
  gets(b);
  ^~~~
In file included from foo.c:1:0:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
foo.c:10:9: warning: unused variable 'k2' [-Wunused-variable]
  int k1,k2;
         ^~
foo.c:10:6: warning: unused variable 'k1' [-Wunused-variable]
  int k1,k2;
      ^~
/tmp/cc6ZcMxl.o: In function `main':
foo.c:(.text.startup+0x1a): warning: the `gets' function is dangerous and should not be used.

自豪的采用jd5进行评测(github.com/masnn/jd5)