题解 | #把字符串转换成整数#

class Solution {
  public:
    int StrToInt(string str) {
        if (str.empty()) {
            return 0;
        }
        int symbol = 1;//标记正负号
        if (str[0] == '-') {
            symbol = -1;
            str[0] = '0';//字符零占位
        }
        if (str[0] == '+') {
            symbol = 1;
            str[0] = '0';//字符零占位
        }
        long long  num = 0;
        for (int i = 0; i < str.size(); i++) {
            if (str[i] < '0'  || str[i] > '9') {
                return 0;
                break;
            } else {
                num = num * 10;
                num = num  + (str[i] - '0');
            }
        }
        num = symbol * num;
        if (num > INT_MAX || num < INT_MIN)
            return 0;
        return num;
    }
};