cropfactor

I have a canon 800D and I am looking at getting a sigma f/1.4 35mm art DG HSM. I have read that this lens works on a crop sensor but does that mean I still times the focal length or will I have the view of 35mm??

Can anyone please tell me for sure if i need to or do not need to apply the 1.6 crop factor to this lens ? Sigma 10-20mm f4-5.6 EX DC HSM as it is specially made for a cropped body as someone has pointed out ? which would make it roughly 16-32mm by my maths on a Canon cropped body if i needed to...