I've always loved maths, especially pure maths, and anything involving logic, so it made sense to do a subject which explores pure maths in depth alongside the logic and deduction involved in Computer Science. I love the satisfaction of understanding the abstract mathematical world, and I love the feeling you get when you create a program that works, no matter what it does. You feel like you're accomplishing something, and while you do that you naturally learn new skills. My best experiences have been in tutorials with our subject tutors. They're really helpful but also the most interesting part of studying here. Our tutors are friendly, care about the subject they're teaching, and are very patient with questions.
This course appealed to me because I was interested in programming but didn't want to give up the logical thinking I love in mathematics. I get to study interesting and rigorous mathematics, to learn and practise programming, but also to apply the mathematical thinking that I have always enjoyed to topics in computer science. Sometimes it feels like this degree takes all the hardest courses from the two subjects - but it's worth it, because those are often the most interesting! It's a varied and sometimes even fun (you read that right!) course.
The Mathematics and Computer Science degree includes a roughly even mix of modules from each subject, with the opportunity to specialise more in the later years. There are both programming and more theoretical computer science courses available, taught through a combination of lectures, tutorials/classes, and programming practicals. The mathematics side doesn't include as many applied courses (especially modules on dynamics/mechanics) as the straight mathematics degree. However, from the second year it offers a lot of choice to study topics that you're interested in from different areas of mathematics. In the second year, everyone takes part in a programming project in groups of about 5 or 6, and in the third and fourth years, there are opportunities to do more independent research. With opportunities like this, the degree puts you in a strong position to decide what you'd like to do after graduating and to be successful in doing it.
I realised this course was right for me was after going to a lecture by Matt Parker about the Maths of Computer Processing. He is a "stand-up" mathematician so he is entertaining to watch. You can find his material on YouTube!
Make sure you read the official prospectus entry for the course which contains entry requirements, full course structure, additional interesting resources and full details of the application process.
If you're going to apply, you'll want to check which Oxford colleges offer this course.