If you are visiting Barcelona, like any other European city you need to give a little bit of thought about your finances. Obviously you will need to change your money into Euros and as aresult you may find yourself carrying large sums of cash on you at any one time. Depending on how long you are going for you can look into buying travellers cheques. Similarly make sure you have a number of bank cards with your fall back being a credit card in case you have a problem with withdrawing money, you do not want to be left with no means of getting cash.
You will be able to pay with your card if it is a vaguely well recognised one like visa, maestro or amex. You do not get charged to pay on card but you will still be subjected to the exchange rate which is not great.