Leetcode:String to Integer(atoi)

这道应该是最经典的一道题了吧

class Solution {
public:
    int myAtoi(string str) {
        int n = str.size();
        long long num = 0;
        int sig = 1;
        int i = 0;
        while(str[i] == ' ' && i < n) ++i;
        if(str[i] == '-'){
            ++i;
            sig = -1;
        }
        else if(str[i] == '+') ++i;
        for(; i != n ;++i){
            if(str[i] > '9' || str[i] < '0')
                break;
            num = 10 * num + (str[i] - '0');
            if((num * sig) > INT_MAX)   return INT_MAX;
            if((num * sig) < INT_MIN)   return INT_MIN;//在循环里判断效果好~
        }
         return num * sig;
    }
};