Strong third-quarter results from tech companies drove investors into stocks Friday, giving the market its third straight weekly gain. The S&P 500 index hit a record. The Nasdaq is the highest it’s been in 13 years. Earnings for companies in the S&P 500 index are expected to grow 4.5 percent compared with the third quarter last year, according to S&P Capital IQ. While respectable, that rate of growth is less than half what was expected at the start of the year. Some market watchers say even that profit growth may not last. They note that much of it is coming from cutting expenses as the global economy remains sluggish.