模拟乘法 

#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <string.h>

#define max 10001
typedef struct
{
    char num[max]; //从低位到高位存储
    int n;         //有多少位
} BigInteger;

//对调位置，使按低位到高位存储
void Reverse(BigInteger *BI)
{
    char tmp;
    for (int i = 0; i < BI->n; i++)
    {
        BI->num[i] -= '0'; //化为整形
    }

    for (int i = 0; i < BI->n / 2; i++)
    {
        tmp = BI->num[i];
        BI->num[i] = BI->num[BI->n - i - 1];
        BI->num[BI->n - i - 1] = tmp;
    }
    return;
}

//相乘的结果存放在multiplicand
void Multiply(BigInteger *multiplicand, BigInteger *multiplier, BigInteger *product)
{
    unsigned char flag; //进位标志
    unsigned char res;
    unsigned char buff[101];//存放中间运算结果
    int cnt;

    //初始化
    product->n = multiplicand->n - 1;
    memset(product->num, 0, product->n);
    //做模拟乘法
    for (int i = 0, j; i < multiplier->n;...