You may not have a code. Some MFG's don't do them any more. This was a big thing starting in the late '90's. It is probably a moot point these days.
The code is/was an anti theft measure. In our old Suburban, and our two old Volvo's, if the radio received no power for a certain length of time, usually less than 1 hour, one had to enter a 4 digit numerical code. Most people never remembered to change it, so it was almost always still four zeros. If the radio needed a code, it would say Enter Code when powered back up, and refuse to work until you gave it the correct one.
Forget I mentioned it. Now the stereo head is probably matched to your computer, and will only work in your car.
I think a lot of the after market stereo's still use a security code though.
130 total pounds of Pitbull ruled by 8 pounds of cat.