Depends on the company. I've been around "big" firms where the engineers all wore button-up shirts, slacks, and non-athletic shoes and had to worry about union rules (e.g., need to use a union employee to move your soldering iron from bench to bench). The smaller firms I've been around are usually more casual. Bare feet are a norm for the engineering types where I work. I tell folks it reduces static problems. When you're at work for 12 to 14 hours, you better be comfortable. Plus, you don't want to get your dressy duds dirty when working around dirty environments.
The smaller firms tend to have flex hours. My last company, this worked out as a major advantage since the field people had nearly 24 hour access to the engineers. The engineers came in anywhere from 7am to 6pm. I always kept some nicer clothes in my file cabinet in case I had to meet a customer.