/in/foo.cc: In function 'int main()':
/in/foo.cc:6:5: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
     gets(s);  // 输入第一行的字符串 s
     ^~~~
In file included from /in/foo.cc:1:0:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/in/foo.cc:6:11: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
     gets(s);  // 输入第一行的字符串 s
           ^
In file included from /in/foo.cc:1:0:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/in/foo.cc:12:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     if (si + len > strlen(s)) {
         ~~~~~~~~~^~~~~~~~~~~
/tmp/ccFCGNgw.o: In function `main':
foo.cc:(.text.startup+0x11): warning: the `gets' function is dangerous and should not be used.