/in/foo.cc: In function 'void w()':
/in/foo.cc:5:8: error: 'void w()' redeclared as different kind of symbol
 void w()
        ^
/in/foo.cc:4:5: note: previous declaration 'int w [21][21][21]'
 int w[N][N][N];
     ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:24:4: error: 'w' cannot be used as a function
  w();
    ^