foo.cc: In function 'int main()':
foo.cc:8:8: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
    8 |  gets(s);
      |        ^
In file included from /usr/include/stdio.h:867,
                 from /usr/include/c++/9/cstdio:42,
                 from /usr/include/c++/9/ext/string_conversions.h:43,
                 from /usr/include/c++/9/bits/basic_string.h:6496,
                 from /usr/include/c++/9/string:55,
                 from /usr/include/c++/9/bits/locale_classes.h:40,
                 from /usr/include/c++/9/bits/ios_base.h:41,
                 from /usr/include/c++/9/ios:42,
                 from /usr/include/c++/9/ostream:38,
                 from /usr/include/c++/9/iostream:39,
                 from foo.cc:1:
/usr/include/x86_64-linux-gnu/bits/stdio2.h:235:1: note: declared here
  235 | gets (char *__str)
      | ^~~~
foo.cc:8:8: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
    8 |  gets(s);
      |        ^
In file included from /usr/include/stdio.h:867,
                 from /usr/include/c++/9/cstdio:42,
                 from /usr/include/c++/9/ext/string_conversions.h:43,
                 from /usr/include/c++/9/bits/basic_string.h:6496,
                 from /usr/include/c++/9/string:55,
                 from /usr/include/c++/9/bits/locale_classes.h:40,
                 from /usr/include/c++/9/bits/ios_base.h:41,
                 from /usr/include/c++/9/ios:42,
                 from /usr/include/c++/9/ostream:38,
                 from /usr/include/c++/9/iostream:39,
                 from foo.cc:1:
/usr/include/x86_64-linux-gnu/bits/stdio2.h:235:1: note: declared here
  235 | gets (char *__str)
      | ^~~~
foo.cc:9:6: error: 'strlen' was not declared in this scope
    9 |  n = strlen(s);
      |      ^~~~~~
foo.cc:2:1: note: 'strlen' is defined in header '<cstring>'; did you forget to '#include <cstring>'?
    1 | #include <iostream>
  +++ |+#include <cstring>
    2 | using namespace std;
foo.cc:24:6: error: 'strcmp' was not declared in this scope
   24 |  if (strcmp(s, t) == 0) {//判断s和t是否相等的函数
      |      ^~~~~~
foo.cc:24:6: note: 'strcmp' is defined in header '<cstring>'; did you forget to '#include <cstring>'?
foo.cc:8:6: warning: ignoring return value of 'char* gets(char*)', declared with attribute warn_unused_result [-Wunused-result]
    8 |  gets(s);
      |  ~~~~^~~

[Hydro](https://hydro.ac)提供评测服务