高精度减法C语言

#include <stdio.h>
#include <string.h>
#include <stdbool.h>
#define N 100010

bool cmp(char str1[], char str2[])
{
    int len1 = strlen(str1);
    int len2 = strlen(str2);
    if (len1 != len2)
        return len1 > len2;
    for (int i = 0; i < len1; i ++ )
    {
        if (str1[i] != str2[i])
            return str1[i] > str2[i];
    }
    return true;
}

void sub(char str1[], char str2[], char sub_high[])
{
    int len1 = strlen(str1);
    int len2 = strlen(str2);
    // 1. 将字符数组转换成整数数组，第0位存储个位数字
    int a[N] = {0};
    int b[N] = {0};
    for (int i = 0; i < len1; i ++ )
        a[i] = str1[len1 - i - 1] - '0';
    for (int i = 0; i < len2; i ++ )
        b[i] = str2[len2 - i - 1] - '0';
    // 2. 减法过程
    int index = 0;
    int res[N] = {0};
    int t = 0; // 借位
    for (int i = 0; i < len1 || i < len2; i ++ )
    {
        if (i < len1) t = a[i] - t;
        if (i < len2) t = t - b[i];
        res[index ++] = (t + 10) % 10;
        if (t >= 0) t = 0;
        else t = 1;
    }
    // 3. 去除前导0
    int happy = 0;
    bool zero_index = true;
    for (int i = index - 1; i >= 0; i -- )
    {
        if (res[i] == 0 && zero_index == true)
            continue;
        else
        {
            zero_index = false; // 结束前导0
            sub_high[happy ++] = res[i] + '0';
        }
    }
    if (zero_index == true)
        strcpy(sub_high, "0");
}

int main()
{
    char str1[N] = "";
    char str2[N] = "";
    char sub_high[N] = "";
    scanf("%s", str1);
    scanf("%s", str2);
    if (cmp(str1, str2))
    {
        sub(str1, str2, sub_high);
        puts(sub_high);
    }
    else
    {
        sub(str2, str1, sub_high);
        printf("-%s\n", sub_high);
    }
    return 0;
}