[google面试题]Write a function to convert a string into an integer

(ThisfunctioniscalledAtoI(oratoi())becauseweareconvertinganASCIIstringintoaninteger.)

Good answer:Go through the string from beginning to end.If the first character is a negative sign,remember this fact.Keep a running total,which starts at 0.Each time your each a new digit,multiply the total by 10 and add the new digit.When you reach the end,return the current total,or,if there was a negative sign,the inverse of the number.Okay answer:Another approach is to go through the string from end to beginning,again keeping a running total.Also,remember a number x representing which digityou are currently on;x is initially 1.For each character,add the current digit times x to the running total,and multiply x by 10.When you reach the beginning,return the current total,or,if there was a negative sign,the inverse of the number.