Strong third-quarter results from tech companies drove stocks higher, giving the market its third straight weekly gain. After reporting results that topped expectations, both Microsoft and Amazon.com rose. Zynga also gained. Most companies that have reported third-quarter earnings are beating estimates. But some market watchers are calling for investors to be cautious, saying that a significant part of the profit growth has come from cutting expenses, not increasing revenue, as the global economy remains sluggish. The government reported that durable goods orders, excluding aircraft and military-related products, fell 1.1 percent.