高精度乘法C语言

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

void mul(char str[], int* u, char high_mul[])
{
    int b = *u;
    int len = strlen(str);
    // 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};
    for (int i = 0; i < len; i ++ )
        a[i] = str[len - i - 1] - '0';
    // 2. 乘法过程
    int index = 0;
    int t = 0; // 进位
    int res[N] = {0};
    for (int i = 0; i < len || t; i ++ )
    {
        if (i < len) t = (a[i] * b) + t;
        res[index ++] = t % 10;
        t = t / 10;
    }
    // 3. 去除前导0
    int high = 0;
    int zero_index = 1;
    for (int i = index - 1; i >= 0; i -- )
    {
        if (res[i] == 0 && zero_index)
            continue;
        else
        {
            zero_index = 0;
            high_mul[high ++] = res[i] + '0';
        }
    }
    if (zero_index)
        strcpy(high_mul, "0");
}

int main()
{
    int b;
    char str[N] = "";
    char high_mul[N] = "";
    scanf("%s", str);
    scanf("%d", &b);
    mul(str, &b, high_mul);
    puts(high_mul);
    return 0;
}