c++ - 链表加法/减法函数正在改变参数的值？

Question

所以在我的 main 中，我有两个多项式 A 和 B，我试图将多项式相加，输出新的多项式，然后从 A 中减去多项式 B，然后输出。但问题是，在加法函数之后，当我调用减法函数时，它对求和多项式而不是新的多项式 A 和 B 执行减法。

main 中的调用

outfile << "Printing addition of the first polynomial and the second polynomial" << endl << endl;
linkedList polynomialD;
polynomialD = polynomialD.polynomialAddition(polynomialA, polynomialB);
polynomialD.printList(outfile);

outfile << endl;
outfile << "Printing subtraction of the second polynomial from the first polynomial" << endl << endl;
linkedList polynomialE;
polynomialE = polynomialE.polynomialSubtraction(polynomialA, polynomialB);
polynomialE.printList(outfile);

这是我的程序输出:

Polynomial in canonical form - 
(6x^6) + (9x^2) + (-5)

Polynomial in canonical form - 
(7x^7) + (2x^5) + (7x^2) + (12)

Printing addition of the first polynomial and the second polynomial

Polynomial in canonical form - 
(7x^7) + (6x^6) + (2x^5) + (16x^2) + (7)


Printing subtraction of the second polynomial from the first polynomial

Polynomial in canonical form - 
(0x^7) + (6x^6) + (0x^5) + (9x^2) + (-5)

但它应该打印:

Polynomial in canonical form - 
(6x^6) + (9x^2) + (-5)

Polynomial in canonical form - 
(7x^7) + (2x^5) + (7x^2) + (12)

Printing addition of the first polynomial and the second polynomial

Polynomial in canonical form - 
(7x^7) + (6x^6) + (2x^5) + (16x^2) + (7)


Printing subtraction of the second polynomial from the first polynomial

Polynomial in canonical form - 
(-7x^7) + (6x^6) + (-2x^5) + (2x^2) + (-17)

出于某种原因，加法函数使其表现得就像它存在一样，因此当它尝试进行减法时，它发现节点当前存在，而它不应该存在。

//Function to insert into the linked list
void listInsert(int coefficient, int exponent)
{
    Node *spot = findSpot (coefficient, exponent);

    if(spot->exponent == exponent )
    {
        int temp;
        temp = spot->coefficient + coefficient;
        spot->coefficient = temp;
    }
    else
    {
        Node* newNode = new Node(coefficient, exponent);
        newNode->next = spot->next;
        spot->next = newNode;
    }
}

//Function used to insert into the linked list but subtracting like powers.
void listInsertSubtraction(int coefficient, int exponent)
{
    Node *spot = findSpot (coefficient, exponent);

    if(spot->exponent == exponent )
    {
        int temp;
        temp = spot->coefficient - coefficient;
        spot->coefficient = temp;        
    }
    else
    {
        int tempcoeff;
        tempcoeff = -coefficient;

        Node* newNode = new Node(coefficient, exponent);
        newNode->next = spot->next;
        spot->next = newNode;
    }
}

//Function to add two polynomials.
linkedList polynomialAddition (linkedList& polynomialA, linkedList& polynomialB)
{
    linkedList newPolynomial = polynomialA;

    //Temporary Nodes point to the first element of each linked list.
    Node* tempNodeB = polynomialB.listHead->next;

    while (tempNodeB != NULL)
    {
        newPolynomial.listInsert (tempNodeB->coefficient, tempNodeB->exponent);
        tempNodeB = tempNodeB->next;
    }
    return newPolynomial;
}

//Function to subtract the 2nd polynomial from the first polynomial.
linkedList polynomialSubtraction (linkedList& polynomialA, linkedList& polynomialB)
{
    linkedList newPolynomial = polynomialA;

    //Temporary Nodes point to the first element of each linked list.
    Node* tempNodeB = polynomialB.listHead->next;

    while (tempNodeB != NULL)
    {
        newPolynomial.listInsertSubtraction (tempNodeB->coefficient, tempNodeB->exponent);
        tempNodeB = tempNodeB->next; 
    }
    return newPolynomial;
}

我试着搞乱并更改通过引用传递给的参数，作为指针，将返回更改为指针而不是值，但是当我尝试运行它时，它只是说运行失败。

编辑:添加 findSpot 函数

Node* findSpot (int coefficient, int exponent)
{
    Node *spot = listHead;

    while(spot->next != NULL && spot->next->exponent >= exponent)
    {
        spot = spot->next;
    }

  return spot;  
}

如果需要，还有指向整个代码的 pastebin 链接 - http://pastebin.com/yL85Xif2

Answer 1

对我来说，当您执行 linkedList newPolynomial = polynomialA; 时，您并不是在创建新列表，而是使用 polynomialA 列表。

如果在加法之后打印 polynomialA，您会看到它已被修改，这就是为什么在减法之后会得到类似 0x^7 的原因。要保留您的算法，您应该复制 polynomialA 并将其用作 newPolynomial。