https://leetcode.com/problems/string-to-integer-atoi/

answer.cc

class Solution {
public:
    int myAtoi(string str) {
        int pos = 0;
        while (str[pos] == ' ' && str[pos] != NULL) {
            pos++;
        }
        if (str[pos] == NULL) {
            return 0;
        }
        char sign = '+';
        if (str[pos] == '+' || str[pos] == '-') {
            sign = str[pos];
            pos++;
        }
        long long result = 0;
        while ('0' <= str[pos] && str[pos] <= '9') {
            result = result * 10 + (str[pos] - '0');
            if (result > INT_MAX) {
                return sign == '+' ? INT_MAX : INT_MIN;
            }
            pos++;
        }
        return sign == '+' ? result : -result;
    }
};