/in/foo.c: In function 'main':
/in/foo.c:6:5: warning: 'gets' is deprecated [-Wdeprecated-declarations]
     gets(s);
     ^~~~
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:10:7: warning: iteration 26 invokes undefined behavior [-Waggressive-loop-optimizations]
   x[k]='a'+k;
   ~~~~^~~~~~
/in/foo.c:8:2: note: within this loop
  for(int k=0;k<=26;k++)
  ^~~
/tmp/ccP95JSP.o: In function `main':
foo.c:(.text.startup+0x1e): warning: the `gets' function is dangerous and should not be used.