PTA 7-23 币值转换

https://pintia.cn/problem-sets/14/problems/803
不太好搞 跟作者对读数的方法的理解有区别

#include <stdio.h>
int x;
int ch[16];
char val[16];
int n = 0;

int findnext(int pos) {
    for (int i = pos; i >= 0; i--) {
//      printf("%d %d ", i, (int)'a' + ch[i]);
        if (ch[i])
            return i;
    }
    return -1;  
}

int findpre(int pos) {
    for (int i = pos + 1; i < n; i++) {
        if (ch[i])
            return i;
    }
    return 0;   
}

int main() {
    while (1) {
        n = 0;
        scanf("%d", &x);
        if (!x)  {
            printf("a\n");
            return 0;
        }
        while (x > 0) {
            int d = x % 10;
            x /= 10;
            ch[n] = d;
            n++;
        }
        
        val[0] = 'S';
        val[1] = 'B';
        val[2] = 'Q';
        val[3] = 'W';
        
        val[4] = 'S';
        val[5] = 'B';
        val[6] = 'Q';
        val[7] = 'Y';
        val[8] = 'S';
        val[9] = 'B';
        val[10] = 'Q';
        
        int aldy = 0;
        for (int i = n - 1; i >= 0; i--) {
            //1000010 一百万零十元 
            //100000010 一亿零十元 
            //100100110 一亿十万一百一十元 
            //20000010 2000010
            bool flag = false;
            
            if (ch[i]) {//ch[i] != 0
                printf("%c", (int)'a' + ch[i]);
                flag = true;
            }
            else if (i % 4 != 0 && i && !aldy){//ch[i] is 0, aldy means 0 is printed in this block, no need print again
                int next = findnext(i);
                int pre = findpre(i); 
                if (next >= 0) {
                    if (i - next < 4) {
                        printf("a");
                        aldy = i;
                        if (aldy > 4) 
                            aldy -= i / 4 * 4;
                    }
                    else if (pre / 4 - i / 4 > 0) {//if the prenon0 is not in the same block as this num.
                        aldy = i;
                        if (aldy > 4) 
                            aldy -= i / 4 * 4;
                        printf("a");
                    }   
                }   
            }
            if (aldy > 0)
                aldy--;
            if(!ch[i])
            if (i % 4 == 0 && findpre(i) - i < 4)
                flag = true;
            if (flag)
                printf("%c", val[i - 1]);
        }
        printf("\n");
    }
  return 0;
}