foo.cc: In function ‘int main()’:
foo.cc:13:29: error: ‘n’ was not declared in this scope
   13 |                         a[++n]=t%2;
      |                             ^
foo.cc:16:32: error: ‘n’ was not declared in this scope
   16 |                 for(int j=1;j<=n;j++)
      |                                ^