foo.cc: In function 'int main()':
foo.cc:6:12: error: expected unqualified-id before numeric constant
  const int 1e4+10
            ^~~
foo.cc:13:3: error: 'a' was not declared in this scope
   a[len]=x%10;
   ^
foo.cc:17:10: error: 'a' was not declared in this scope
  int fir=a[len];
          ^
foo.cc:25:24: error: lvalue required as left operand of assignment
   if(k!=len&&i=(len-k+1))
                        ^