The car will not start all the time,battery and starter are working

Do you mean won't start or won't crank. If it cranks and won't start it could be fuel or spark. In a no start condition crank over the engine and check for spark at a spark plug, and check then for fuel at the fuel rail by cracking open the fuel rail line. If it is a no crank condition verify power at the starter wire if there is power the switch and circuit is OK and the starter is most likely bad.