foo.cc: In function 'int main()':
foo.cc:26:6: error: 'n' was not declared in this scope
   if(n*(n-1)*(n-3)==0) u=0;
      ^
foo.cc:27:6: error: 'n' was not declared in this scope
   if(n*(n-1)*(n-3)<0) u=-1;
      ^