剑指Offer——把字符串转换成整数

 1 class Solution {
 2 public:
 3     int StrToInt(string str) {
 4         int strLen = str.length();
 5         if(strLen == 0) return 0;
 6         int res = 0;
 7         if(str[0] == ‘+‘ || str[0] == ‘-‘) res = 0;
 8         else if(str[0] >= ‘0‘ && str[0] <= ‘9‘) res = str[0] - ‘0‘;
 9         for(int i = 1; i < strLen; i++) {
10             if(str[i] < ‘0‘ || str[i] > ‘9‘) return 0;
11             res *= 10;
12             res += str[i] - ‘0‘;
13         }
14         return str[0] == ‘-‘ ? -res : res;
15     }
16 };