Depends on the uni. UNSW offers a civil engineering degree with a minor in architecture. USYD offers a combined degree where you get a civil engineering degree and degree in architecture.

Math is completely different. You do learn a lot harder math in uni, but the problems you do in math subjects are typically a lot easier than the difficulty you get in the HSC. In terms of the math in engineering - it's not that hard. Most of it is straightforward applications of formulas, and doesn't require anything intensive. What's important is understanding how to use the formula and how to solve the problem.

Civil engineering is a huge field, and probably has one of the most jobs in the engineering field. Everything you see around you was essentially designed by civil engineers - structural engineering for buildings, traffic engineers and road planners for street layouts, stormwater engineers for drainage, etc.

Here's an example of a HW problem I had in engineering.

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Here's a snippet of part of the solution:

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Notice how the calculations themselves are very simple and just involve plugging numbers into formulas. What's more important is knowing how to use the formulas to get to the answer. That's essentially what math in engineering is - it's mostly number crunching.