Pat class B 1019 digital black hole (20 points) (possible causes of measurement point errors)

1019 Digital black hole (20 branch )

Given any number that is not exactly the same 4 Positive integer , If we put 4 Numbers are sorted in non incremental order , And then in non decreasing order , Then use the 1 A number minus 2 A digital , Will get a new number . Keep doing this again and again , We will soon stop having “ Digital black hole ” It's called.  6174, This magic number is also called Kaprekar constant .

for example , We from 6767 Start , Will get

7766 - 6677 = 1089
9810 - 0189 = 9621
9621 - 1269 = 8352
8532 - 2358 = 6174
7641 - 1467 = 6174
... ...

Any 4 Positive integer , Please write a program to demonstrate the process of reaching the black hole .

Input format ：

Type to give a  (0,104)  A positive integer in an interval  N.

Output format ：

If  N  Of 4 The digits are all equal , Then output... In one line  N - N = 0000; Otherwise, each step of the calculation will be output in one line , until  6174  Appear as a difference , See the example for the output format . Pay attention to each number press  4  Bit format output .

sample input 1：

6767

No blank lines at the end

sample output 1：

7766 - 6677 = 1089
9810 - 0189 = 9621
9621 - 1269 = 8352
8532 - 2358 = 6174

No blank lines at the end

sample input 2：

2222

No blank lines at the end

sample output 2：

2222 - 2222 = 0000

No blank lines at the end

This is my initial code ：

#include <iostream>
#include <algorithm>
using namespace std;
int max(int a[])
{
    return a[3]*1000+a[2]*100+a[1]*10+a[0];
}
int min(int a[])
{
    return a[0]*1000+a[1]*100+a[2]*10+a[3];
}
void to_array(int n,int a[])
{
    int cnt=0;
    while (n) {  
        a[cnt++]=n%10;
        n/=10;
    }
}
int main()
{
    int n;
    cin>>n;
    int a[100];
    while (1) {
        to_array(n,a);
        sort(a,a+4);
        int maxn=max(a);int minn=min(a);
        n=maxn-minn;
        printf("%04d - %04d = %04d\n",maxn,minn,n);
        if (n==0||n==6174) break;
    } 
}

There is a problem that local measuring points cannot pass , Thought for a long time , It is found that you can see from the input instructions in the title , The input is not necessarily 4 digit ,0-10000 We should meet all the requirements , For two digits 24, It should be regarded as 0024 Look at , After two steps of operation, we get 6714;

So which section of the corresponding code is wrong ？ stay int to array In the conversion function of ！！ Revised as follows ：

void to_array(int n,int a[])
{
//    int cnt=0;
//    while (n) { // Can't calculate 0 until , If it's a two digit number , Should be automatically added to the array 0; 
//        a[cnt++]=n%10;
//        n/=10;
//    }
	for (int i=0;i<4;i++) {
		a[i]=n%10;
		n/=10;
	}
}

The effect of front and back operation is as follows ：

 Before the change ：
24
-1119662172 - 7470512 = -1127132684
-2468 - -8642 = 6174

--------------------------------
Process exited after 1.877 seconds with return value 0
 Please press any key to continue . . .

 After modification ：
24
4200 - 0024 = 4176
7641 - 1467 = 6174

--------------------------------
Process exited after 1.366 seconds with return value 0
 Please press any key to continue . . .