Zurich city transport fare mode

No, they take single fare tickets, or day passes, or weekly or monthly passes. A Swiss Pass also works. You can buy them out of vending machines with a credit card. My own experience is that for something like a day ticket, the transaction is small enough that a PIN will not be required. They also take Swiss coins, and since coins go up to 5 CHF, that is usually not a problem. The machines are also multi-lingual (including English). If you have Swiss Half Fare Card, you indicate that during the purchase process and you pay half.
It is totally on an honor system, you don't need to show your ticket to anyone, just have it on you. Occasionally, a fare inspector will board and flash a badge and everyone will dig out their ticket or pass and show it to the inspector. Don't have a ticket? Expect to pay a minimum 50 CHF (or so) fine on the spot along with the fare and have your ID recorded. Next time you're caught, the fine will be bigger.
Mostly they have trams and S-bahn trains. The region is divided into zones. When you buy a ticket, you pay according to how many zones you cross in a trip, plus the zone you start in. The central zone, which is most of Zurich city proper, counts as 2 zones. So, if I remember rightly, you cross 1 zone boundary from central Zurich to the airport, so you buy a 3-zone ticket to get to the airport, using either a train or the trams. A day pass is the equivalent to a round trip ticket cost.
Information at: https://www.stadt-zuerich.ch/vbz/en/index/tickets/tickets_prices.html

"Do they accept credit cards in city buses" - they don't accept anything on buses (or trams which are more common) because you must buy your ticket before you get on the tram/bus/train. The driver does not sell tickets.
As Sam says, the ticket machines take coins and give change, and some take notes (and give change) or credit cards. The best deal is to buy a one-day card from the first ticket machine you encounter. If you are staying overnight in a hotel within Zürich city limits, you will get a free pass from the hotel for the duration of your stay.