/in/foo.cc: In function 'int main()':
/in/foo.cc:12:19: error: 'n' was not declared in this scope
  int left=1,right=n,mid;
                   ^
/in/foo.cc:15:5: error: 'mid' was not declared in this scope
   a[mid]=(left+right)/2;
     ^~~
/in/foo.cc:20:14: error: invalid types 'int [100001][std::ios_base&(std::ios_base&)]' for array subscript
 cout<<a[right];
              ^