If you have extra money to take abroad, consider taking it.
Austria is part of the European Union and adopted the Euro in 2002. It is a good idea for you to procure some Euros before arrival. Most students use cash and all ATMs accept American bank cards.
Note that there is a small service charge when withdrawing from an ATM, as well as when using credit cards.
Major credit cards (Visa, Mastercard, and American Express) are accepted in most stores and restaurants. However, it is common for smaller shops and grocery stores to accept cash only.
It is best if you have both options readily available.