leetcode---String to Integer (atoi)

Implement atoi to convert a string to an integer.

Hint: Carefully consider all possible input cases. If you want a challenge, please do not see below and ask yourself what are the possible input cases.

Notes: It is intended for this problem to be specified vaguely (ie, no given input specs). You are responsible to gather all the input requirements up front.

class Solution {public:    bool isNum(char a)    {        if(a < '0' || a > '9')            return false;        return true;    }    int myAtoi(string str) {        int result = 0;        int len = str.length();        int flag;        int i = 0;        while(str[i] == ' ') //去掉前面的空格            i++;        if((str[i] == '+' || str[i] == '-') && (str[i+1] == '+' || str[i+1] == '-'))        {            return 0;        }        else if(str[i] == '-')        {            flag = -1;            i++;        }        else if(str[i] == '+')        {            flag = 1;            i++;        }        else        {            flag = 1;        }        while(str[i] == '0')  //去掉前面的0            i++;        int j = i;        for(; i<len; i++)        {            if(!isNum(str[i]))                break;            result = result * 10 + str[i] - '0';            if(i-j >= 10 || result < 0)  //溢出                if(flag > 0)                    return pow(2,31) - 1;                else                    return pow(2, 31) * (-1);        }        return result * flag;    }};