/in/foo.cc:68:11: warning: character constant too long for its type
   freopen(FILE_NAME+'.in', "r", stdin);
           ^~~~~~~~~
/in/foo.cc:68:21: warning: multi-character character constant [-Wmultichar]
   freopen(FILE_NAME+'.in', "r", stdin);
                     ^~~~~
/in/foo.cc:69:11: warning: character constant too long for its type
   freopen(FILE_NAME+'.out', "w", stdout);
           ^~~~~~~~~
/in/foo.cc:69:21: warning: multi-character character constant [-Wmultichar]
   freopen(FILE_NAME+'.out', "w", stdout);
                     ^~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:68:20: error: invalid conversion from 'int' to 'const char*' [-fpermissive]
   freopen(FILE_NAME+'.in', "r", stdin);
                    ^
In file included from /usr/include/c++/6/cstdio:42:0,
                 from /usr/include/x86_64-linux-gnu/c++/6/bits/stdc++.h:46,
                 from /in/foo.cc:1:
/usr/include/stdio.h:280:14: note:   initializing argument 1 of 'FILE* freopen(const char*, const char*, FILE*)'
 extern FILE *freopen (const char *__restrict __filename,
              ^~~~~~~
/in/foo.cc:69:20: warning: integer overflow in expression [-Woverflow]
   freopen(FILE_NAME+'.out', "w", stdout);
                    ^
/in/foo.cc:69:20: error: invalid conversion from 'int' to 'const char*' [-fpermissive]
In file included from /usr/include/c++/6/cstdio:42:0,
                 from /usr/include/x86_64-linux-gnu/c++/6/bits/stdc++.h:46,
                 from /in/foo.cc:1:
/usr/include/stdio.h:280:14: note:   initializing argument 1 of 'FILE* freopen(const char*, const char*, FILE*)'
 extern FILE *freopen (const char *__restrict __filename,
              ^~~~~~~