LeeCode-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:
    int myAtoi(string str) {
    long long cur=0;
    int num=0,i=0;
    int flag1=0,flag2=0;
    while(str[i]!='' && str[i]==' ') i++;
    if(str[i]=='-') flag1++,i++;
    else if(str[i]=='+') flag2++,i++;
    for(; str[i]!=''; i++)
    {
        if(str[i]>='0' && str[i]<='9')
        {
            if(flag1==2)
            {
                cur=cur*10-(str[i]-'0');
                if(cur<-2147483648) return -2147483648;
            }
            else if(flag1==1) cur=-str[i]+'0',flag1++;
            else
            {
                cur=cur*10+(str[i]-'0');
                if(cur>2147483647) return 2147483647;
            }
        }
        else break;
    }
    num=(int)cur;
    return num;
    }
};