Python:a = input()
if a.count(a[0])==4:print(a,'-',a,'=','0000')
else:while(True):a = a.zfill(4)b = ''.join(sorted(a,reverse=True))c = ''.join(sorted(a))a = str(int(b) - int(c))a = a.zfill(4)print(b,'-',c,'=',a)  #或者用方法print("%4d"%12)  输出0012if(a=='6174'):break

C:#include <stdio.h>int main(){char a[4]={'0','0','0','0'},b[4],c[4],tmp;int i,j,num,a2,b2,c2;scanf("%s",&a);for(i=0;i<4;i++)if(a[i] == '\0')a[i] = '0';if(a[0]==a[1] && a[0] == a[1] && a[0]==a[2]){printf("%c%c%c%c - %c%c%c%c = 0000",a[0],a[1],a[2],a[3],a[0],a[1],a[2],a[3]);return 0;}while(1){for(i=0;i<3;i++){for(j=i+1;j<4;j++){if(a[i]>=a[j]){tmp = a[i];a[i] = a[j];a[j] = tmp;}}c[i] = a[i];}c[3] = a[3];for(i=0;i<3;i++){for(j=i+1;j<4;j++){if(a[i]<=a[j]){tmp = a[i];a[i] = a[j];a[j] = tmp;}}b[i] = a[i];}b[3] = a[3];b2=c2=0;for(i=3,num=1;i>=0;i--){b2 += (b[i]-'0')*num;c2 += (c[i]-'0')*num;num *= 10;
        }a2 = b2-c2;for(i=3;i>=0;i--){a[i] = a2%10 + '0';a2 /= 10;}printf("%c%c%c%c - %c%c%c%c = %c%c%c%c\n",b[0],b[1],b[2],b[3],c[0],c[1],c[2],c[3],a[0],a[1],a[2],a[3]);if(b2-c2 == 6174)break;}return 0;
}

C++: //别人分享的代码
#include <iostream>
#include <string>
#include <algorithm>
#include <sstream>using namespace std;string int2string(int ival)
{stringstream stream;       //创建一个stringstream,  即可以用来输入，也可用来输出数据stream << ival;               //将int型值传给stringstream，return stream.str();         //stringstream的成员函数str()  返回一个相应的字符串
}int main()
{string num_str;cin >> num_str;if(num_str.size() != 4)  // 输入数据不满4位，则要添加0补满4位
    {num_str.append(4 - num_str.size(), '0');}while(true){// 先检查数字字符是否全部一样if(num_str.find_first_not_of(num_str[0]) == string::npos){cout << num_str << " - " << num_str << " = " << "0000" << endl;break;    // 结束循环
        }// 数字字符升序排序
        sort(num_str.begin(), num_str.end());int num_ascend = stoi(num_str);// 数字字符降序排序
        reverse(num_str.begin(), num_str.end());int num_descent = stoi(num_str);if(num_ascend != num_descent)  // 四位数字不全相同情况
        {if(num_descent - num_ascend == 6174){cout << num_descent << " - " << num_ascend << " = "<< 6174 << endl;break;   // 结束循环
            }else    //差不为6174
            {string num_ascend_str = int2string(num_ascend);if(num_ascend_str.size() != 4)  // 控制输出的格式，必须有4位填充满num_ascend_str.insert(0, 4 - num_ascend_str.size(), '0');cout << num_descent << " - " << num_ascend_str << " = "<< num_descent - num_ascend << '\n';num_str = int2string(num_descent - num_ascend);}}}return 0;
}