The Black Hole of Numbers (strtoint+inttostr+sort)

For any 4-digit integer except the ones with all the digits being the same, if we sort the digits in non-increasing order first, and then in non-decreasing order, a new number can be obtained by taking the second number from the first one. Repeat in this manner we will soon end up at the number 6174 -- the "black hole" of 4-digit numbers. This number is named Kaprekar Constant.

For example, start from 6767, we'll get:

7766 - 6677 = 1089

9810 - 0189 = 9621

9621 - 1269 = 8352

8532 - 2358 = 6174

7641 - 1467 = 6174

... ...

Given any 4-digit number, you are supposed to illustrate the way it gets into the black hole.

Input Specification:

Each input file contains one test case which gives a positive integer N in the range (0, 10000).

Output Specification:

If all the 4 digits of N are the same, print in one line the equation "N - N = 0000". Else print each step of calculation in a line until 6174 comes out as the difference. All the numbers must be printed as 4-digit numbers.

Sample Input 1:

6767

Sample Output 1:

7766 - 6677 = 1089

9810 - 0189 = 9621

9621 - 1269 = 8352

8532 - 2358 = 6174

Sample Input 2:

2222

Sample Output 2:

2222 - 2222 = 0000

坑点1、数字都要四位的2、如果是判断下一个式子的差不等于上个结果，然后跳出的话，那么需要判断，是不是第一次输出。比如，输入6174，结果就等于6174，那么就会没输出，直接跳出。

 #include <iostream>

 #include <algorithm>

 #include<string>

 #include <sstream>

 #include <iomanip>

 using namespace std;

 int a1[];

 int a2[];

 int bb[];

 bool cmp1(int a,int b)

 {

    return a>b;

 }

 bool cmp2(int a,int b)

 {

    return a<b;

 }

 int main()

 {

       string n;

       int i;

       while(cin>>n)

       {

          int tt,c1,c2;

          stringstream ss1;

          ss1<<n;

          ss1>>tt;

          i=;

          bool fir=true;

          while(true)

          {

                   string ss;

                   stringstream ss2;

                   ss2<<setfill('')<<setw()<<tt;

                   ss2>>ss;

                   for(i=;i<ss.length();i++)

                   {

                  a1[i]=ss[i]-'';

                    a2[i]=a1[i];

                   }

              sort(a1,a1+ss.length(),cmp1);

                sort(a2,a2+ss.length(),cmp2);

                    c1=; c2=;

                for(i=;i<ss.length();i++)

                   {

                    c1=c1*+a1[i];

                      c2=c2*+a2[i];

                   }

                   if(c1-c2==tt&&!fir)  break;

                   else 

                   {

                         fir=false;

                         cout<<setfill('')<<setw()<<c1<<" - "<<setfill('')<<setw()<<c2<<" = "<<setfill('')<<setw()<<c1-c2<<endl;

                         tt=c1-c2;

                   }     

          }  

       }

    return ;

 }