/in/foo.cc:18:11: error: '::main' must return 'int'
 void main()
           ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:22:2: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
  gets(a);
  ^~~~
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:22:8: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
  gets(a);
        ^
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__;
              ^~~~