分段错误c++十六进制计算器

当我试图将十六进制数添加到当前十六进制数时，我一直遇到分段错误。这是我遇到分割错误的地方（我想）：

newHex->insertTail(sum);

以下是整个程序：

#include <iostream>
#include <vector>
#include <stdlib.h>
#include <string>
using namespace std;
#undef NULL
const int NULL = 0;
const char SENTINEL = '#';
typedef int element;
class listnode {
    public:
        element data;
        listnode * next;
};
class LList {
    private:
        listnode * head;
        listnode * tail;
        listnode * view;
    public:
        LList();
        ~LList();
        void read();
        listnode* next();
        void print();
        void insertTail(element val);
        void clean();
        //void add(LList operand);
        //void multiply(LList operand);
        element deleteHead();
};
class Calculator {
    public:
        Calculator();
        LList* add(LList& left, LList& right);
        //LList* multiply(LList& left, LList& right);
};
Calculator::Calculator() {
};
LList* Calculator::add(LList& left, LList& right) {
    int sum, carry = 0, lval = 0, rval = 0;
    bool calculating = true;
    listnode *leftNode;
    listnode *rightNode;
    LList* newHex;
    while(calculating) {
        leftNode = left.next();
        rightNode = right.next();
        if(leftNode == NULL) {
            lval = 0;
        }
        else
            lval = leftNode->data;
        if(rightNode == NULL) {
            rval = 0;
        }
        else
            rval = rightNode->data;

        if(leftNode == NULL && rightNode == NULL) {
            calculating = false;
            if(carry != 0) {
                newHex->insertTail(carry);
            }
            break;
        }
        sum = lval + rval + carry;
        carry = 0;
        if(sum >= 16) {
            carry = 1;
            sum -= 16;
        }
        cout << "Segmentation Fault Below :)"  << endl;
        newHex->insertTail(sum);
    }
    return newHex;
};
listnode* LList::next() {
    listnode* temp = view;
    if(temp != NULL)
        view = view->next;
    if(view == NULL) {
    }
    return temp;
};

LList::LList(){
    head = NULL;
    view = NULL;
};

void LList::print() {
    listnode * temp;
    int i = 0;
    string printValues;
    temp = head;
    while(temp != NULL) {
        int var = temp -> data;
        char character = ' ';
        if(i % 3 == 0 && i != 0)
            printValues += ',';
        i++;    
        if(var > 9 && var < 16)
        {
            character = static_cast <char>(var + 65 - 10);
        }else if (var <= 9 && var >= 0)
            character = static_cast <char>(var + 48);
        printValues += character;
        temp = temp -> next;
    }
    string tempValues;
    for(int i = printValues.length() - 1; i >= 0; i--)
        tempValues += printValues[i];
    cout << tempValues;
    cout << endl;
};
 void LList::read() {
    string userval;
    int i;
    bool parsing = true;
    char curval;
    vector <int> values;
    clean();
    while(parsing) {
        cin >> userval;
        for(unsigned int i = 0; i < userval.length(); i++) {
            curval = userval[i];    //this is your character
            if(curval >= 48 && curval <= 57)
                values.push_back(static_cast <int>(curval - 
            48));
            if(curval >= 65 && curval <= 70)
                values.push_back(static_cast <int>(curval - 
            65 + 10));
            if(curval == ' ')
                break;
            if(curval == SENTINEL) {
                parsing = false;
                break;
            }   
        }
    }
    for(int i = values.size() -1; i >= 0; i--) {
        insertTail(values[i]);
    }
}; 
void LList::insertTail(element val) {
    listnode * temp;
    temp = new listnode;
    temp -> data = val;
    temp -> next = NULL;
    if(head == NULL) {
        head = temp;
        view = head;
    }
    else
        tail -> next = temp;
    tail = temp;
};
void LList::clean() {
    while(head != NULL)
        deleteHead();
};
void validCommands() {
    cout << "Valid commands are:" << endl;
    cout << "  e enter  enter the current ";
    cout << "hexadecimal ";
    cout << "number from the keyboard" << endl;
    cout << "  a add        add a new hexadecimal ";
    cout << "number to the current hex. number" << endl;
    cout << "  m multiply   ";
    cout << "multiply a new hexadecimal number ";
    cout << "by the current hex. number" << endl;
    cout << "  h help   show this help menu" << endl;
    cout << "  q quit   quit the program" << endl << endl;
};
/*
void LList::multiply(LList operand) {
    int left, right, product, carry;
    listnode* operandNext = operand.next();
    listnode* currentNode = this->head;
    while(operandNext != NULL) {
        left = operandNext->data;
        right = currentNode->data;
        product = left * right;
        carry = 0;
        if(product >= 16) {
            product -= 16;
            carry = 1;
        }
        if(currentNode == NULL) {
            this->insertTail(left);
        }
        currentNode->data = product;
        currentNode = currentNode->next;
        operandNext = operandNext->next;
    }
};
*/
element LList::deleteHead() {
    listnode * temp;
    temp = head;
    head = head -> next;
    delete temp;
    return temp -> data;
};
LList::~LList(){
    delete head;
};
int main() {
    LList L, add,multiply;
    Calculator calc;
    L.insertTail(0);
    char option;
    bool run;
    cout << "Hexadecimal Calculator, Ver 1.0.0 n";
    cout << endl;

    do {
    cout << "Current Hexadecimal number is: ";
    L.print();
    cout << endl;
    cout << "Command (h for help): ";
    cin >> option;
    cout << endl << endl;
        switch(option) {
            case 'e' : 
                cout << "Enter a hexadecimal number ";
                cout << "followed by #: ";
                L.read();
                cout << endl << "Entering completed.";
                cout << endl << endl;
            break;
            case 'a' :  
                cout << "Adding a new hexadecimal number ";
                cout << "to the current hex. number" << endl;
                cout << endl;
                cout << "Enter a hexadecimal ";
                cout << "number, follow by #: ";
                add.read();
                cout << endl << "Addition completed.";
                cout << endl;
                L = *calc.add(L, add);
                cout << endl;
                break;
            case 'm' : 
                cout << "Multiplying a new hexadecimal ";
                cout << "number ";
                cout << "to the current hex. number" << endl;
                cout << endl;
                cout << "Enter a hexadecimal ";
                cout << "number, follow by #: ";
                //multiply.read();
                cout << endl << "Multiplication completed.";
                cout << endl;
                //L.multiply(multiply);
                cout << endl;
                break;
            case 'h' : validCommands();
            break;
            case 'q' : run = false;
            break;
        };
    } while (run);
        exit(0);
}