foo.c: In function 'main':
foo.c:19:2: warning: 'gets' is deprecated [-Wdeprecated-declarations]
   19 |  gets(s1)!='\0';
      |  ^~~~
In file included from /usr/include/stdio.h:867,
                 from foo.c:1:
/usr/include/x86_64-linux-gnu/bits/stdio2.h:235:1: note: declared here
  235 | gets (char *__str)
      | ^~~~
foo.c:19:10: warning: comparison between pointer and zero character constant [-Wpointer-compare]
   19 |  gets(s1)!='\0';
      |          ^~
foo.c:19:2: note: did you mean to dereference the pointer?
   19 |  gets(s1)!='\0';
      |  ^
foo.c:19:10: warning: value computed is not used [-Wunused-value]
   19 |  gets(s1)!='\0';
      |  ~~~~~~~~^~~~~~
foo.c:20:2: warning: 'gets' is deprecated [-Wdeprecated-declarations]
   20 |  gets(s2)!='\0';
      |  ^~~~
In file included from /usr/include/stdio.h:867,
                 from foo.c:1:
/usr/include/x86_64-linux-gnu/bits/stdio2.h:235:1: note: declared here
  235 | gets (char *__str)
      | ^~~~
foo.c:20:10: warning: comparison between pointer and zero character constant [-Wpointer-compare]
   20 |  gets(s2)!='\0';
      |          ^~
foo.c:20:2: note: did you mean to dereference the pointer?
   20 |  gets(s2)!='\0';
      |  ^
foo.c:20:10: warning: value computed is not used [-Wunused-value]
   20 |  gets(s2)!='\0';
      |  ~~~~~~~~^~~~~~
foo.c: In function 'Diff':
foo.c:14:1: warning: control reaches end of non-void function [-Wreturn-type]
   14 | }
      | ^
/usr/bin/ld: /tmp/ccmZjw4E.o: in function `main':
foo.c:(.text.startup+0x4e): warning: the `gets' function is dangerous and should not be used.

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