If you did not close MATLAB after the unfortunate edit, it might be possible to reverse the edits by using the ‘undo' arrow (counter-clockwise arrow in the rightmost part of the Editor top toolstrip, also implemented by CTRL+Z) as many times as necessary to restore the original code. Alternatively, look at the cylinder function, since they might have common code.
It‘s a core MATLAB function, so another option is to Contact Support and ask MathWorks to send you a copy. If worst comes to worst, re-install MATLAB.
Regardless, you have my sympathies!
