If you want to study real and complex analysis, a classic text is W. Rudin's "Real and complex analysis". In fact pretty much anything by Rudin is excellent.
A more accessible title of Rudin is "Principles of Mathematical Analysis".
Another classic complex analysis book is by Alfors, although the title by Stewart and Tall, both called "Complex analysis", might be more accessible (and slightly more modern in its approach).
These are all introductory (1st year mathematics undergraduate) texts - for UK universities.
Rudin's "Real and complex analysis" does contain advanced material, and is probably not suitable as an introductory text for an engineering student. Worth a look, just in case.