想问一下，测试点2通不过是什么原因，注意不需要自己另写代码（但可以在我的代码基础上修改），找出代码问题出在哪儿，或者出问题的测试数据是什么，答非所问者不予采纳

PAT 乙级 1019 千名教师建设，万道高质量题目，百万用户拼题的程序设计实验辅助教学平台 https://pintia.cn/problem-sets/994805260223102976/problems/994805302786899968

我的代码

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;

bool cmp(int a, int b)
{
    return a > b;
}
int main()
{
    int a, res[10];
    cin >> a;
    if (a == 6174) printf("7641 - 1467 = 6174\n");
    int z = a;
    int j = 0;
    while (z)
    {
        res[j ++ ] = z % 10;
        z /= 10;
    }
    bool flag = false;
    for (int n = 0; n < j; n ++ )
        if (res[n] != res[0])
        {
            flag = true;
            break;
        }
    memset(res, 0, sizeof res);
    
    if (!flag) printf("%d - %d = 0000", a, a);
    else
    {
        while (a != 6174)
        {
            int i = 0, x, y;
            while (a)
            {
                res[i ++ ] = a % 10;
                a /= 10;
            }
            sort(res, res + 4, cmp);
            x = res[0] * 1000 + res[1] * 100 + res[2] * 10 + res[3];
            y = res[3] * 1000 + res[2] * 100 + res[1] * 10 + res[0];
            a = x - y;
            printf("%04d - %04d = %04d\n", x, y, a);
            memset(res, 0, sizeof res);
        }
    }
    return 0;
}

改好了，有帮助望采纳，谢谢！

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
bool cmp(int a, int b)
{
    return a > b;
}
int main()
{
    int a, res[10];
    cin >> a;
    if (a == 6174) printf("7641 - 1467 = 6174\n");
    if(a<10) a*=1000; //改的地方一 
    int z = a;
    int j = 0;
    while (z)
    {
        res[j ++ ] = z % 10;
        z /= 10;
    }
    bool flag = false;
    for (int n = 0; n < j; n ++ )
        if (res[n] != res[0])
        {
            flag = true;
            break;
        }
    memset(res, 0, sizeof res);
    if (!flag) printf("%04d - %04d = 0000", a, a); //改的地方二 
    else
    {
        while (a != 6174)
        {
            int i = 0, x, y;
            while (a)
            {
                res[i ++ ] = a % 10;
                a /= 10;
            }
            sort(res, res + 4, cmp);
            x = res[0] * 1000 + res[1] * 100 + res[2] * 10 + res[3];
            y = res[3] * 1000 + res[2] * 100 + res[1] * 10 + res[0];
            a = x - y;
            printf("%04d - %04d = %04d\n", x, y, a);
            memset(res, 0, sizeof res);
        }
    }
    return 0;
}

题主考虑的太复杂了，前面的判断冗余了,修改如下，供参考：

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
bool cmp(int a, int b)
{
    return a > b;
}
int main()
{
    int a, res[4] = {0};
    cin >> a;
    /*if (a == 6174) printf("7641 - 1467 = 6174\n");
    //int z = a;
    //int j = 0; 
    //while (z)
    //{
    //    res[j++] = z % 10;
    //    z /= 10;
    //}
    //bool flag = false;
    //for (int n = 0; n < j; n++)
    //    if (res[n] != res[0])
    //    {
    //        flag = true;
    //        break;
    //    }
    //memset(res, 0, sizeof res);
    //if (!flag) printf("%d - %d = 0000", a, a);
    //else
    //{*/
        while (1)// while (a != 6174)
        {
            int i = 0, x, y;
            while (a)
            {
                res[i++] = a % 10;
                a /= 10;
            }
            sort(res, res + 4, cmp);
            x = res[0] * 1000 + res[1] * 100 + res[2] * 10 + res[3];
            y = res[3] * 1000 + res[2] * 100 + res[1] * 10 + res[0];
            a = x - y;
            printf("%d%d%d%d", res[0], res[1], res[2], res[3]);
            printf(" - %d%d%d%d = %04d\n", res[3], res[2], res[1], res[0], a);
            memset(res, 0, sizeof(res));
            if (a == 6174 || a == 0)   //这里增加循环退出判断
                break;
        }
    //}
    return 0;
}