What is the difference between the Audi A1 and A4 models?

I am considering buying an Audi and am confused between the A1 and A4 models. Can someone explain the main differences between these two models including engine, pricing, and features?

The main difference between the Audi A1 and A4 models is size. The A1 is a subcompact car, whereas the A4 is a compact car. The A4 is also more powerful with a range of engine options. Pricing for the A4 is typically higher due to its larger size and more advanced features.