poj 1350 Cabric Number Problem

#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
#include <math.h>
using namespace std;
int to_int(vector<char> coll)
{
    int sum=0;
    for(int i=0;i<coll.size();i++)
        sum+=(coll[i]-48)*pow(10.0,i);
    return sum;
}
void to_vec(vector<char>& coll,int n)
{
    while(n)
    {
        coll.push_back(char(n%10+48));
        n=n/10;
    }
}
int main()
{
    string data;int i,max,min,dis,t;
    while(cin>>data&&data!="-1")
    {
        cout<<"N="<<data<<":\n";
        if(data.size()!=4||data.find_first_not_of(data[0])==string::npos)
        {
            printf("No!!\n");
            continue;
        }

        t=0;
        vector<char> digit;
        for(i=0;i<data.size();i++)
            digit.push_back(data[i]);
        do 
        {
            sort(digit.begin(),digit.end());
            max=to_int(digit);
            reverse(digit.begin(),digit.end());
            min=to_int(digit);
            dis=max-min;
            printf("%d-%d=%d\n",max,min,dis);
            t++;
            digit.clear();
            to_vec(digit,dis);
        }while (dis!=0&&dis!=6174);
        
        printf("Ok!! %d times\n",t);
    }
    return 0;
}