LeetCode Day7 String_to_integer

class Solution {
public:
    int myAtoi(string str) {
        int index=0,sign=1,total=0;
        //empty string
        if(str.length()==0)    return 0;
        //remove blank
        while(str[index]==' ' && index<str.length())    index++;
        //sign
        if(str[index]=='+' || str[index]=='-')
            sign=(str[index++]=='+')?1:-1;
        //convert number
        while(index < str.length() && str[index] >= '0' && str[index] <= '9'){
            if(total>INT_MAX/10 || (total==INT_MAX/10 && str[index] - '0' > INT_MAX%10))
                return (sign==1)?INT_MAX:INT_MIN;
            total=total*10+str[index++] - '0';
        }
        return total*sign;
    }
};