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.

Requirements for atoi:

The function first discards as many whitespace characters as necessary until the first non-whitespace character is found. Then, starting from this character, takes an optional initial plus or minus sign followed by as many numerical digits as possible, and interprets them as a numerical value.

The string can contain additional characters after those that form the integral number, which are ignored and have no effect on the behavior of this function.

If the first sequence of non-whitespace characters in str is not a valid integral number, or if no such sequence exists because either str is empty or it contains only whitespace characters, no conversion is performed.

If no valid conversion could be performed, a zero value is returned. If the correct value is out of the range of representable values, INT_MAX (2147483647) or INT_MIN (-2147483648) is returned.

int myAtoi(string str) {        char Char[100];        strcpy(Char, str.c_str());        int sign = 1, base = 0, i = 0;        while (Char[i] == ' ') { i++; }//一直找到第一个非空字符        if (Char[i] == '-' || Char[i] == '+') {            sign = 1 - 2 * (Char[i++] == '-'); //考虑到数据的符号，将+、-转换为+1、-1，最终乘        }        while (Char[i] >= '0' && Char[i] <= '9') {//筛选出有效字符            if (base >  INT_MAX / 10 || (base == INT_MAX / 10 && Char[i] - '0' > 7)) {//判断是否越界，因为最后一个数字还没计算进来，所以除以10                if (sign == 1) return INT_MAX;//根据符号判断越上界还是下界                else return INT_MIN;            }            base  = 10 * base + (Char[i++] - '0');//每筛选出来一个有效字符，将原base*10再加新的有效字符，Char[i++] - '0'利用ASCII值将字符型转换成数字        }        return base * sign;//根据base和符号返回对应的值 }

note:

c_str()是c++中string类（class）的函数，它能把string类的对象里的字符串转换成c中char型变量的字符串，这是为了与c语言兼容，在c语言中没有string类型，故必须通过string类对象的成员函数c_str()把string 对象转换成c中的字符串样式。

还可能有其他情况需要考虑：-+i      +-i