【問題描述】 設計一個實現任意長的整數進行加法運算的演示程式 。
【基本要求】 利用雙向迴圈連結串列實現長整數的儲存，每個結點含一個整形變數。輸入和輸出形式：按中國對於長整數的表示習慣，每四位一組，組間用逗號隔開。
【測試資料】
（1）0；0；應輸出“0”。
（2）-2345,6789；-7654,3211；應輸出“-1,0000,0000”。
（3）-9999,9999；1,0000,0000,0000；應輸出“9999,0000,0001”。
（4）1,0001,0001；-1,0001,0001；應輸出“0”。
（5）1,0001,0001；-1,0001,0000；應輸出“1”。
（6）-9999,9999,9999；-9999,9999,9999；應輸出“-1,9999,9999,9998”。
（7）1,0000,9999,9999；1；應輸出“1,0001,0000,0000”。

加法運算分為同號和異號兩部分，具體實現程式碼如下：

#include "stdio.h"
#include "stdlib.h"
#include "conio.h"
#include "ctype.h"

typedef struct DualNode
{
    int data;
    struct DualNode *prior, *next;
}DualNode, *DualList;

DualList InitList(int sign)
{
    //頭結點存放符號位，1為正，-1為負
    DualList L;
    L = (DualList)malloc(sizeof(DualNode));
    L->
 
next = L->prior = L;
    L->data = sign;
    return L;
}

void InsertNodeAtTail(DualList L, int data)
{
    //尾插，用於儲存資料的輸入
    DualNode *s;
    s = (DualList)malloc(sizeof(DualNode));
    s->data = data;
    s->next = L;
    s->prior = L->prior;
    L->prior->next = s;
    L->
 
prior = s;
}

void InsertNodeAtHead(DualList L, int data)
{
    // 即插在頭結點之後，用於計算結果的儲存
    DualNode *s;
    s = (DualList)malloc(sizeof(DualNode));
    s->data = data;
    s->next = L->next;
    s->prior = L;
    L->next->prior = s;
    L->next = s;
}

void PrintList(DualList L)
{
    //列印結果
    int FirstTime = 1;
    DualNode *p = L;
    if (p->data == -1) printf("-");
    p = p->next;
    while(p != L)
    {
        if (FirstTime)
        {
            FirstTime = 0;
            printf("%d", p->data);
        }
        else
        {
            printf(",%4d", p->data);
        }
        p = p->next;
    }
    printf("\n");
}

DualList InputData()
{
    int FirstNum = 1, data;
    char c;
    DualList L;
    L = (DualList)malloc(sizeof(DualNode));
    L->next = L->prior = L;
    printf("Please Input as Format: -1234,1234,1234\n");
    if ((c = getchar()) == '-')
        L = InitList(-1);
    else
        L = InitList(1);
    if (isdigit(c))
        // 退格處理
        ungetc(c, stdin);
    do{
        scanf("%d", &data);
        InsertNodeAtTail(L, data);
    }while((c = getchar()) != '\n');
    printf("Your Input is:\n");
    PrintList(L);
    return L;
}

void DelNode(DualList L, DualNode *p)
{
    p->prior->next = p->next;
    p->next->prior = p->prior;
    free(p);
}

void Add(DualList a, DualList b, DualList c)
{
    DualList pa, pb;
    int carry = 0, tmp;
    pa = a->prior;
    pb = b->prior;
    while((pa != a) && (pb != b))
    {
        tmp = pa->data + pb->data + carry;
        if (tmp >= 10000)
        {
            carry = 1;
            tmp -= 10000;
        }else
            carry = 0;
        InsertNodeAtHead(c, tmp);
        pa = pa->prior;
        pb = pb->prior;
    }
    while(pa != a)
    {
        // pb = b
        tmp = pa->data + carry;
        if (tmp >= 1000)
        {
            carry = 1;
            tmp -= 10000;
        }
        else
            carry = 0;
        InsertNodeAtHead(c, tmp);
        pa = pa->prior;
    }
    while(pb != b)
    {
        // pa = a
        tmp = pb->data + carry;
        if (tmp >= 1000)
        {
            carry = 1;
            tmp -= 10000;
        }
        else
            carry = 0;
        InsertNodeAtHead(c, tmp);
        pb = pb->prior;
    }
    if (carry != 0)
        InsertNodeAtHead(c, 1);
}

void Sub(DualList a, DualList b, DualList c)
{
    DualList pa, pb, pc;
    int borrow = 0,tmp;
    pa = a->prior;
    pb = b->prior;
    while((pa != a) && (pb != b))
    {
        if (pa->data >= pb->data + borrow)
        {
            tmp = pa->data - pb->data - borrow;
            borrow = 0;;
        }
        else
        {
            tmp = 10000 + pa->data - pb->data - borrow;
            borrow = 1;
        }
        InsertNodeAtHead(c, tmp);
        pa = pa->prior;
        pb = pb->prior;
    }
    if (pa != a || (pa == a && pb == b && borrow == 0))
    {
       // a >= b
        c->data = a->data;
    }
    if (c->data != a->data)
    {
        // a < b
        pc = c->prior;
        while(pc != c)
        {
            // 結果轉換
            if (pc == c->prior)
                pc->data = 10000 - pc->data;
            else
                pc->data = 9999 - pc->data;
            pc = pc->prior;
        }
        // 因為符號判斷錯誤，所以borrow要取反
        borrow = borrow?0:1;
        while(pb != b)
        {
            if (pb->data >= borrow)
            {
                tmp = pb->data - borrow;
                borrow = 0;
            }
            // 繼續借位
            else
            {
                tmp = 10000 + pb->data + borrow;
                borrow = 1;
            }
            InsertNodeAtHead(c, tmp);
            pb = pb -> prior;
        }
    }
    else{
        // a>b
        while(pa != a)
        {
            if (pa->data >= borrow)
            {
                tmp = pa->data - borrow;
                borrow = 0;
            }
            else
            {
                tmp = 10000 - pa->data - borrow;
                borrow = 1;
            }
            InsertNodeAtHead(c, tmp);
            pa = pa->prior;
        }
    }
    pc = c->next;
    while(pc->next !=c && pc->data == 0)
    {
        pc = pc->next;
        DelNode(c, pc->prior);
    }
}

DualList AddList(DualList a, DualList b)
{
    DualList c;
    if (a->data * b->data > 0)
    {
        c = InitList(a->data);
        Add(a, b, c);
    }else
    {
        c=InitList(b->data);
        Sub(a, b, c);
    }
    return c;
}

int main(int argc, char const *argv[])
{
    while(1)
    {
        //便於測試
        DualList a, b, c;
        a = InputData();
        b = InputData();
        c = AddList(a, b);
        printf("The result is:");
        PrintList(c);
    }
    return 0;
}