字符串处理
#include<iostream>
#include<algorithm>
using namespace std;
char cmp(char a,char b){
return a>b;}
int main()
{
string s;
cin>>s;
s.insert(0,4-s.size(),'0');
do{
string s1=s,s2=s;
sort(s1.begin(),s1.end(),cmp);
sort(s2.begin(),s2.end());
int a1=stoi(s1),a2=stoi(s2);
s=to_string(a1-a2);
s.insert(0,4-s.size(),'0');
cout<<s1<<" - "<<s2<<" = "<<s<<endl;
}while(s!="0000" && s!="6174");
return 0;
}