[剑指offer] 49. 把字符串转换成整数

class Solution
{
  public:
    int StrToInt(string str)
    {
        if (str == "")
            return 0;
        int s = 1;
        int curInd = 0;
        if (str[curInd] == ‘-‘)
        {
            s = -1;
            curInd++;
        }
        else if (str[curInd] == ‘+‘)
        {
            s = 1;
            curInd++;
        }
        int sum = 0;
        for (; curInd < str.length(); curInd++)
        {
            if (str[curInd] < 48 || str[curInd] > 57)
                return 0;
            sum = sum * 10 + str[curInd] - 48;
        }
        return sum * s;
    }
};