/in/foo.c: In function 'judge':
/in/foo.c:5:10: warning: implicit declaration of function 'strlen' [-Wimplicit-function-declaration]
  int len=strlen(m);
          ^~~~~~
/in/foo.c:5:10: warning: incompatible implicit declaration of built-in function 'strlen'
/in/foo.c:5:10: note: include '<string.h>' or provide a declaration of 'strlen'
/in/foo.c: In function 'main':
/in/foo.c:23:2: warning: 'gets' is deprecated [-Wdeprecated-declarations]
  gets(m);
  ^~~~
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__;
              ^~~~
/tmp/cc4aRIfi.o: In function `main':
foo.c:(.text.startup+0x59): warning: the `gets' function is dangerous and should not be used.