My cat is vomiting and has diarrhea he is 10 and a cross persian! help :(?

It's been going on for 2 days now.. we rescued him last month as his owner was taken in to hospital and was unable to care for him therefor we don't know his medical back ground. I want him to be happy and comfortable and he has been until now im a bit worried purely because of his age just wondering if anyone can shed some light on the situation before i take him to the vets tomorrow. thank-you