数据结构C++，线性表学习

#include <iostream>
#include <sstream>
#include <algorithm>
#include <iterator>
#include <cmath>

template<class T>
struct chainNode{
    T element;
    chainNode<T> *next;
    chainNode() {}
    chainNode(const T& element) {
        this->element = element;
    }
    chainNode(const T& element, chainNode<T>* next) {
        this->element = element;
        this->next = next;
    }
};

template<class T>
class linearList{
public:
    virtual ~linearList() {}
    virtual bool empty() const = 0;
    virtual int size() const = 0;
    virtual T& get(int theIndex) const = 0;
    virtual int indexOf(const T& theElement) const = 0;
    virtual void erase(int theIndex) = 0;
    virtual void insert(int theIndex, const T& theElement) = 0;
    virtual void output(std::ostream& out) const = 0;
};

template<class T>
class chain:public linearList<T> {
public:
    chain(int initialCapacity = 10);
    chain(const chain<T>&);
    ~chain();

    bool empty() const {return listSize == 0;}
    int size() const {return listSize;}
    T& get(int theIndex) const;
    int indexOf(const T& theElement) const;
    void erase(int theIndex);
    void insert(int theIndex, const T& theElement);
    void output(std::ostream& out) const;
protected:
    void checkIndex(int theIndex) const;
    chainNode<T>* firstNode;
    int listSize;
};

template<class T>
chain<T>::chain(int initialCapacity) {
    if(initialCapacity < 1) {
        std::ostringstream s;
        s<<"Initial capacity = "<<initialCapacity<<" must be > 0";
        return;
    }
    firstNode = NULL;
    listSize = 0;
}

template<class T>
chain<T>::chain(const chain<T>& theList) {
    listSize = theList.listSize;
    if(listSize == 0) {
        firstNode = NULL;
        return;
    }
    chainNode<T>* sourceNode = theList.firstNode;
    firstNode = new chainNode<T>(sourceNode->element);
    sourceNode = sourceNode->next;
    chainNode<T>* targetNode = firstNode;

    while(sourceNode != NULL) {
        targetNode->next = new chainNode<T>(sourceNode->element);
        targetNode = targetNode->next;
        sourceNode = sourceNode->next;
    }
    targetNode->next = NULL;
}

template<class T>
chain<T>::~chain() {
    while(firstNode != NULL) {
        chainNode<T>* nextNode = firstNode->next;
        delete firstNode;
        firstNode = nextNode;
    }
}

template<class T>
void chain<T>::checkIndex(int theIndex) const {
    if(theIndex<0 || theIndex>=listSize) {
        std::ostringstream s;
        s<<"index = "<<theIndex<<" size = "<<listSize;
        return;
    }
}

template<class T>
T& chain<T>::get(int theIndex) const {
    checkIndex(theIndex);

    chainNode<T>* currentNode = firstNode;
    for(int i=0; i<theIndex; i++) {
        currentNode = currentNode->next;
    }
    return currentNode->element;
}

template<class T>
int chain<T>::indexOf(const T& theElement) const {
    chainNode<T>* currentNode = firstNode;
    int index=0;
    while(currentNode != NULL && currentNode->element != theElement) {
        currentNode = currentNode->next;
        index++;
    }
    if(currentNode == NULL)
        return -1;
    else
        return index;
}

template<class T>
void chain<T>::erase(int theIndex) {
    checkIndex(theIndex);

    chainNode<T>* deleteNode;
    if(theIndex == 0) {
        deleteNode = firstNode;
        firstNode = firstNode->next;
    } else {
        chainNode<T>* p = firstNode;
        for(int i=0; i<theIndex-1; i++)
            p = p->next;
        deleteNode = p->next;
        p->next = p->next->next;
    }
    listSize--;
    delete deleteNode;
}

template<class T>
void chain<T>::insert(int theIndex, const T& theElement) {
    if(theIndex<0 || theIndex>listSize) {
        std::ostringstream s;
        s<<"index = "<<theIndex<<" size = "<<listSize;
        return;
    }
    if(theIndex == 0) {
        firstNode = new chainNode<T>(theElement, firstNode);
    } else {
        chainNode<T>* p=firstNode;
        for(int i=0; i<theIndex; i++)
            p = p->next;
        p->next = new chainNode<T>(theElement, p->next);
    }
    listSize++;
}

template<class T>
void chain<T>::output(std::ostream& out) const {
    for(chainNode<T>* currentNode=firstNode; currentNode != NULL; currentNode = currentNode->next)
        out<<currentNode->element<<" ";
}

template<class T>
std::ostream& operator<<(std::ostream& out, const chain<T>& x) {
    x.output(out);
    return out;
}

int main() {
    int a[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};

    chain<int> mychain(10);
    for(int i=0; i<sizeof(a)/sizeof(a[0]); i++) {
        std::cout<<i<<": "<<a[i]<<"\n";
        mychain.insert(0, a[i]);
    }
    std::cout<<mychain;

    return 0;
}