/in/foo.cc: In function 'int main()':
/in/foo.cc:22:5: error: redefinition of 'int main()'
 int main()
     ^~~~
/in/foo.cc:4:5: note: 'int main()' previously defined here
 int main()
     ^~~~
/in/foo.cc:27:8: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
 gets(a1);
        ^
In file included from /usr/include/c++/7/cstdio:42:0,
                 from /usr/include/c++/7/ext/string_conversions.h:43,
                 from /usr/include/c++/7/bits/basic_string.h:6159,
                 from /usr/include/c++/7/string:52,
                 from /usr/include/c++/7/bits/locale_classes.h:40,
                 from /usr/include/c++/7/bits/ios_base.h:41,
                 from /usr/include/c++/7/ios:42,
                 from /usr/include/c++/7/ostream:38,
                 from /usr/include/c++/7/iostream:39,
                 from /in/foo.cc:1:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~