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.

题目只考虑了"    123"或者"+123","-123"，而不考虑"abs123"等情况，所以一开始只要排除空格，然后直接判断正负号，接着读取数字字符即可。

但是要考虑溢出，int占四个字节，32位，取值范围是-2147483648~2147483647；

若超过了负数则 输出-2147483648  超过了正数则输出2147483647
在科普一个知识点，倘若某个数超过了2147483647则会变为负数，反过来一样

int myAtoi(char *str) {
    while(*str == 32) str++;
    if((*str != '-' && *str != '+') && (*str < '0' || *str >'9')) return 0;
    int t = 1;
    long long result = 0;
    if(*str == '-'){
        t = -1;
        str++;
    }else if(*str == '+'){
        str++;
    }
    while(*str >= '0' && *str <= '9'){
        result = result*10 + (*str - '0');
        if(t == -1 && result >= 2147483648){
            result = 2147483648;
            break;
        }
        if(result > 2147483647){
            result = 2147483647;
            break;
        }
        str++;
    }
    result *= t;
    return result;
}