字符串中找出連續出現的最大數字字符串

#define _CRT_SECURE_NO_WARNINGS 1
#include<iostream>
using namespace std;
#include<string>
int main()
{
    string s1;
    while (getline(cin, s1))
    {
        int newlen = 0;//統計數字字符的長度
        int max=0;//數字字符的最大長度
        auto start = s1.begin();
        auto finish = s1.begin();
        string s2;
        while (start != s1.end()&&finish!=s1.end())
        {
            if (*start >= '0'&&*start <= '9')
            {
                newlen = 0;
                finish = start;
                while (finish != s1.end() && *finish >= '0'&&*finish <= '9'&&finish != s1.end())
                    //算出從當前位置起連續數字的最大值
                {
                    finish++;
                    newlen++;
                }
                if (newlen > max)//如果比之前的最大值大則替換
                {
                    s2.clear();
                    while (start != finish)
                    {
                        s2.push_back(*start);
                        start++;
                    }
                    max = newlen;
                }
                else//沒之前的大就讓start繼續往后走
                {
                    start++;
                }
            }
            else
            {
                start++;
            }
        }
        cout << s2 << endl;
        s1.clear();
        s2.clear();
    }
    system("pause");
    return 0;
}