PAT 1069. The Black Hole of Numbers (20)

#include<vector>
#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<cstdlib>
#include<queue>
#include<map>
#include<stack>
using namespace std;
#define INF 100000000
#define min(a,b) a<b?a:b
void chang(int a[],int n)
{
a[0]=n/1000;
a[1]=(n%1000)/100;
a[2]=(n%100)/10;
a[3]=n%10;
}
int main()
{

int n;
int a[6],l,m;
int t=0;
l=m=0;
scanf("%d",&n);
int s=6174;
chang(a,n); sort(a,a+4);
if(a[0]==a[1]&&a[1]==a[2]&&a[2]==a[3])
printf("%d - %d = %04d\n",n,n,t);

else
{
while(l-m!=s)
{

l=a[0]+a[1]*10+a[2]*100+a[3]*1000;
m=a[0]*1000+a[1]*100+a[2]*10+a[3];
printf("%04d - %04d = %04d\n",l,m,l-m);
chang(a,l-m);
sort(a,a+4);
}

}

return 0;
}