I'm 56. i quit smoking about a year ago but now, when i talk for longer than 5 or 10 minutes, or shout loudly, my throat becomes quite sore (much worse and for much longer after any shouting). do i have throat cancer?

What you described is not a sign of cancer. Given your long term history of smoking, it would be prudent to see a doctor for a general assessment of your health. For healthy diet: http://www.choosemyplate.gov/., exercise 30 minutes/day, drink enough water daily so your urine is mostly colorless, have safe sex, no tobacco alcohol weed or street drugs.

While cancer cannot be ruled out, there are other relatively benign conditions that will have to be ruled in or out such as swelling of the vocal cords or laryngitis, for example. Having a thorough ENT (ORL) exam might suffice in establishing a firm diagnosis.