题解 | #把字符串转换成整数#

class Solution {
public:
int StrToInt(string str) {

    int size = str.size();
    if (size == 0)
        return 0;
    int res = 0;
    char temp = str[0];
    int flag = 1;
    int start = 0;

    if (temp == '+' || temp == '-') {
        start = 1;
        if (temp == '+')
            flag = 1;
        else
            flag = -1;
    }

    for (int i = start; i < size; ++i) {
        if (str[i] - '0' > 9 || str[i] - '0' < 0) {
            return 0;
        }        
        else {
            res = 10 * res + flag * (str[i] - '0');
        }
    }
    return res;
}

};