C语言基础：用快速排序实现输出最大数

//此函数用来寻找从右往左第1位~第K位数字中最大的数//因为数组长度较小，采用递归排序的非链表方法#include <stdio.h>#include <ctype.h>#include <stdbool.h>#define div 10#define N 10typedef int cat;cat digit(cat n, cat k);   //拆分函数void quick_sort(cat a[], cat low, cat high);cat split(cat a[], cat low, cat high);cat main(void){    cat i, e, num_re;    printf("please enter the number: \n");    scanf("%d", &i);   //注意这里输入的是一串连续数字    printf("please enter the digit you want: \n");    scanf("%d", &e);  //输入位数k    num_re = digit(i,e);    if (num_re != 0){  //判断返回值是否为真    printf("the number you want is: %d ", num_re);    }    else{        printf("Please enter the digit within the range\a");    }    return 0;}cat digit(cat n, cat k)  //定义两个形式参数n,k{    cat num = 0;    cat arr[div], g, temp, status;    if(n)    {        status = n;        for(g = 0; g <= k; g++)   //先将数字拆分成单个字符存入数组        {            temp  = status % 10;  //寻找个位数            status /= 10;   //从右向左减少一位            arr[g] = temp;            printf("%d\n", arr[g]);            //g++;        }        quick_sort(arr, 0, k);//第三个参数的长度为变量K可以减少排序位数        num = arr[k]; //注意这里不用-1        return num;    }    else{        printf("Please enter the right digit");        return 0;    }}//使用快速排序返回最大值void quick_sort(cat a[], cat low, cat high){    cat temp;    if (low >= high){        return;    }    else{        temp = split(a, low, high);        quick_sort(a, 0, temp - 1);        quick_sort(a, temp + 1, high);    }}cat split(cat a[], cat low, cat high){    cat value = a[low];    for(;;)    {        while (low < high && value <= a[high])            high--;        if (low >= high) {//为什么去掉大于号，函数无解                break;}        a[low++] = a[high];        //low++;        while (low < high && value >= a[low])            low++;        if (low >= high) break;        a[high--] = a[low];        //high--;    }    a[low] = value;    return low;}/* 此为原快速排序代码main函数体cat main(void){    cat a[N], i;    printf("Please enter %d number of sorting: ", N);    for(i = 0; i < N; i++)    {        scanf("%d", &a[i]);    }    quick_sort(a, 0, N - 1);    printf("In sorted order: ");    for(i = 0; i < N; i++)    {        printf("%d \n", a[i]);    }    return 0;}*/