foo.cc:11:1: error: 'Copy' does not name a type
 Copy
 ^~~~
foo.cc: In function 'int main()':
foo.cc:44:5: error: redefinition of 'int main()'
 int main()
     ^~~~
foo.cc:5:5: note: 'int main()' previously defined here
 int main(){
     ^~~~
foo.cc: At global scope:
foo.cc:55:1: error: 'Copy' does not name a type
 Copy
 ^~~~
In file included from foo.cc:58:0:
/usr/include/c++/7/cstring:75:11: error: '::memchr' has not been declared
   using ::memchr;
           ^~~~~~
/usr/include/c++/7/cstring:76:11: error: '::memcmp' has not been declared
   using ::memcmp;
           ^~~~~~
/usr/include/c++/7/cstring:77:11: error: '::memcpy' has not been declared
   using ::memcpy;
           ^~~~~~
/usr/include/c++/7/cstring:78:11: error: '::memmove' has not been declared
   using ::memmove;
           ^~~~~~~
/usr/include/c++/7/cstring:79:11: error: '::memset' has not been declared
   using ::memset;
           ^~~~~~
/usr/include/c++/7/cstring:80:11: error: '::strcat' has not been declared
   using ::strcat;
           ^~~~~~
/usr/include/c++/7/cstring:81:11: error: '::strcmp' has not been declared
   using ::strcmp;
           ^~~~~~
/usr/include/c++/7/cstring:82:11: error: '::strcoll' has not been declared
   using ::strcoll;
           ^~~~~~~
/usr/include/c++/7/cstring:83:11: error: '::strcpy' has not been declared
   using ::strcpy;
           ^~~~~~
/usr/include/c++/7/cstring:84:11: error: '::strcspn' has not been declared
   using ::strcspn;
           ^~~~~~~
/usr/include/c++/7/cstring:85:11: error: '::strerror' has not been declared
   using ::strerror;
           ^~~~~~~~
/usr/include/c++/7/cstring:86:11: error: '::strlen' has not been declared
   using ::strlen;
           ^~~~~~
/usr/include/c++/7/cstring:87:11: error: '::strncat' has not been declared
   using ::strncat;
           ^~~~~~~
/usr/include/c++/7/cstring:88:11: error: '::strncmp' has not been declared
   using ::strncmp;
           ^~~~~~~
/usr/include/c++/7/cstring:89:11: error: '::strncpy' has not been declared
   using ::strncpy;
           ^~~~~~~
/usr/include/c++/7/cstring:90:11: error: '::strspn' has not been declared
   using ::strspn;
           ^~~~~~
/usr/include/c++/7/cstring:91:11: error: '::strtok' has not been declared
   using ::strtok;
           ^~~~~~
/usr/include/c++/7/cstring:92:11: error: '::strxfrm' has not been declared
   using ::strxfrm;
           ^~~~~~~
/usr/include/c++/7/cstring:93:11: error: '::strchr' has not been declared
   using ::strchr;
           ^~~~~~
/usr/include/c++/7/cstring:94:11: error: '::strpbrk' has not been declared
   using ::strpbrk;
           ^~~~~~~
/usr/include/c++/7/cstring:95:11: error: '::strrchr' has not been declared
   using ::strrchr;
           ^~~~~~~
/usr/include/c++/7/cstring:96:11: error: '::strstr' has not been declared
   using ::strstr;
           ^~~~~~
foo.cc:62:5: error: redefinition of 'int n'
 int n;
     ^
foo.cc:18:5: note: 'int n' previously declared here
 int n;
     ^
foo.cc: In member function 'NUM NUM::operator=(int)':
foo.cc:66:9: error: 'memset' was not declared in this scope
         memset(s, 0, sizeof(s));
         ^~~~~~
foo.cc:66:9: note: suggested alternative: 'wmemset'
         memset(s, 0, sizeof(s));
         ^~~~~~
         wmemset
foo.cc: In member function 'NUM NUM::operator+(NUM)':
foo.cc:73:9: error: 'memset' was not declared in this scope
         memset(y.s, 0, sizeof(y.s));
         ^~~~~~
foo.cc:73:9: note: suggested alternative: 'wmemset'
         memset(y.s, 0, sizeof(y.s));
         ^~~~~~
         wmemset
foo.cc: In function 'int main()':
foo.cc:96:5: error: redefinition of 'int main()'
 int main()
     ^~~~
foo.cc:5:5: note: 'int main()' previously defined here
 int main(){
     ^~~~
foo.cc: In function 'int main()':
foo.cc:48:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d",&n);
     ~~~~~^~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:98:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d", &n);
     ~~~~~^~~~~~~~~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。