Problems with mod function to find remainder

I'm a beginner and having problems with my code I don't quite understand. The first option in my switch menu is not working and I have tried numerous tweaks to no avail. I've removed the if else statement, altered the "second" variable between constant = 0 and not constant, a few other things as well.

This code is supposed to reverse the digits in an integer. If the integer is less than 10, i.e. 2, the 2 becomes 20. I'm not achieving anything close to that.

                cout << "Please enter a number between 0 and 99\n";
                cin >> num;
                if (num < 9)
                    num *= 10;
                else
                    num += 0;
                while (num !=0)
                {
                    remainder = num%10;
                    second = remainder*10 + remainder;
                    num /= 10;
                }
                cout << num << " reverses to make " << second << endl;