/in/foo.c: In function 'main':
/in/foo.c:23:2: warning: 'gets' is deprecated [-Wdeprecated-declarations]
  gets(s1);
  ^~~~
In file included from /in/foo.c:1:0:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/in/foo.c:24:2: warning: 'gets' is deprecated [-Wdeprecated-declarations]
  gets(s2);
  ^~~~
In file included from /in/foo.c:1:0:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/in/foo.c:71:3: warning: implicit declaration of function 'system' [-Wimplicit-function-declaration]
   system("pause");
   ^~~~~~
/in/foo.c:19:12: warning: unused variable 'l' [-Wunused-variable]
  int i,j,k,l;
            ^
/tmp/ccYKm7MT.o: In function `main':
foo.c:(.text.startup+0x29): warning: the `gets' function is dangerous and should not be used.