Alternatives would be starter going bad - usually car will click when you turn the key, but nothing else happens. This can also indicate a loose connection with the battery, as well, so both would be checked.
For the alternator, if the lights are running dim, interior lights running dim, radio acting flaky, power windows slow responding/working, car is hard or slow to crank, or the batt/gen light is on, its time to check it. The battery will keep running out of a charge after a few hours/days of use and needing to be jumped. If you have power but the car won't crank, its usually an issue with the battery itself, not the alternator. The battery gets the car started, the alternator keeps it going, runs the electrical stuff, and recharges the battery hold its charge.