C++ Linked List Implementation Using Template

Templates in C++ is a tool for generic programming. In general we want to make program that is independent of input type (integer, real, strings etc.).

Here we want to create a List class that in generic in nature and works or all sort of input type like strings , integers, float, double, chars etc.

#include <iostream>
#include <string>
using namespace std;

template <class T> class List;

template <class T>
class Node
{
    friend class List<T>;
    T val;
    Node<T> *link; 
    public:
        Node() {}
        Node(T v) : val(v), link(NULL) {}
        Node(T v, Node<T> *p) : val(v), link(p) {}
};

template <class T>
class List
{
    int size;
    Node<T> *head;
    public:
        List() : size(0) {
            head = new Node<T>();
        }
        void append(T);
        void prepend(T);
        void insertAt(T, int);
        void show() const;
        inline int len() { return size; }
};

template <class T>
void List<T>::append(T item)
{
    Node<T> *pivot = new Node<T>(item);
    if (size == 0) {
        head->link = pivot;
    }
    else {
        Node<T> *temp = head;
        while (temp->link != NULL) {
            temp = temp->link; 
        }
        temp->link = pivot;
    }
    size++;
}

template <class T>
void List<T>::insertAt(T item, int pos)
{
    Node<T> *pivot = new Node<T>(item);

    if (pos <= size+1 && pos > 0) {
        int i = 0;
        Node<T> *temp = head, *prev;
        while (i != pos) {
            ++i;
            prev = temp;
            temp = temp->link;
        }
        pivot->link = temp;
        prev->link = pivot;
        size++;
    }
    else {
        cerr << "Invalid Position '" << pos << "' Sprecified." << endl;
    }
}

template <class T>
void List<T>::prepend(T item)
{
    Node<T> *pivot = new Node<T>(item);
    if (size == 0) {
        head->link = pivot;
    }
    else {
        Node<T> *temp = head->link;
        head->link = pivot;
        pivot->link = temp;
    }
    size++;
}

template <class T>
void List<T>::show() const
{
    Node<T> *tmp = head->link;
    cout << "[";
    while (tmp != NULL) {
        cout << tmp->val << "," << ends;
        tmp = tmp->link;
    }
    cout << "\b\b]" << endl;
}

int main()
{
    List<int> a;
    
    a.append(2);
    a.append(3);
    a.prepend(1);
    a.append(5);
    a.show();
    a.insertAt(-1, 0);
    a.insertAt(4, 4);
    a.insertAt(6, 6);
    a.show();
    cout << "Length Of The List Of Integers: " << a.len() << endl;
    
    List<string> b;
    
    b.append("Cat");
    b.append("Dog");
    b.append("Mouse");
    b.append("Bird");
    b.show();
    cout << "Length Of The List Of Strings: "<< b.len() << endl;
    
    return 0;   
}

[1, 2, 3, 5]
Invalid Position '0' Sprecified.
[1, 2, 3, 4, 5, 6]
Length Of The List Of Integers: 6
[Cat, Dog, Mouse, Bird]
Length Of The List Of Strings: 4

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