foo.cc: In function ‘int main()’:
foo.cc:26:5: error: expected ‘,’ or ‘;’ before ‘for’
   26 |     for (int mask=1;mask<(1<<n);mask++)
      |     ^~~
foo.cc:26:21: error: ‘mask’ was not declared in this scope
   26 |     for (int mask=1;mask<(1<<n);mask++)
      |                     ^~~~