C++ || Snippet – Custom Template Linked List Sample Code

This page will consist of sample code for a singly linked list, which is loosely based on the built in C++ “List” library. Provided in the linked list class are the following functions:
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* PushFront - Adds new item to the front of the list (LIFO) * PushBack - Adds new item to the back of the list (FIFO) * PopFront - Returns & removes first item from the list * PopBack - Returns & removes last item from the list * Front - Returns (but does not delete) the first item from the list * Back - Returns (but does not delete) the last item from the list * Delete - Searches and deletes the requested item * Display - Display all the current contents in the list * Replace - Replaces existing item from the list with a new item If existing item cannot be found, the new item is added to the back of the list * InsertBefore - Inserts new item before the existing item. If existing item cannot be found, the new item is added to the back of the list * InsertAfter - Inserts new item after the existing item. If existing item cannot be found, the new item is added to the back of the list * InsertInOrder - Inserts new item in numerical order, from lowest to highest * Size - Return the current size of the list * MakeEmpty - Initializes the list to an empty state
From the following, the functions of interest to look out for are the “Delete, Display, Replace, InsertBefore, InsertAfter, and InsertInOrder” functions as they are typically used as programming assignments in many C++ Data structures courses to further demonstrate how linked lists operate.
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// ============================================================================// Author: Kenneth Perkins// Date: Jul 26, 2012// Taken From: http://programmingnotes.org/// File: LinkedList.h// Description: This is a class which implements various functions which// demonstrates the use of a Linked List. // ============================================================================#include <iostream> template <class ItemType>class LinkedList{public: LinkedList(); /* Function: Constructor initializes list Precondition: None Postcondition: Defines private variables */ bool IsEmpty(); /* Function: Determines whether queue is empty Precondition: List has been created Postcondition: The function = true if the list is empty and the function = false if list is not empty */ void PushFront(ItemType item); /* Function: Adds new item to the front of the list (LIFO) Precondition: List has been created and is not full Postcondition: Item is in the list */ void PushBack(ItemType item); /* Function: Adds new item to the back of the list (FIFO) Precondition: List has been created and is not full Postcondition: Item is in the list */ ItemType PopFront(); /* Function: Returns & removes first item from the last Precondition: List has been initialized Postcondition: The first item in the list is removed */ ItemType PopBack(); /* Function: Returns & removes last item from the list Precondition: List has been initialized Postcondition: The last item in the list is removed */ ItemType Front(); /* Function: Returns (but does not delete) the first item from the list Precondition: List has been initialized Postcondition: The first item in the list is removed */ ItemType Back(); /* Function: Returns (but does not delete) the last item from the list Precondition: List has been initialized Postcondition: The last item in the list is removed */ void Delete(ItemType item); /* Function: Searches and deletes the requested item Precondition: List has been created and is not empty Postcondition: Item removed from the list */ void Display(); /* Function: Display all the current contents in the list Precondition: List has been created and is not empty Postcondition: List is displayed to the screen */ void Replace(ItemType initial, ItemType replace); /* Function: Replaces existing item from the list with a new item Precondition: List has been created and is not empty Postcondition: Initial item is replaced with the new one */ void InsertBefore(ItemType initial, ItemType newItem); /* Function: Inserts new item before the existing item Precondition: List has been created and is not empty Postcondition: New item is inserted before the existing item */ void InsertAfter(ItemType initial, ItemType newItem); /* Function: Inserts new item after the existing item Precondition: List has been created and is not empty Postcondition: New item is inserted after the existing item */ void InsertInOrder(ItemType item); /* Function: Inserts new item in numerical order, from lowest to highest Precondition: List has been created and is not empty Postcondition: The list is sorted in numerical order */ int Size(); /* Function: Return the current size of the list Precondition: List has been initialized Postcondition: The size of the list is returned */ void MakeEmpty(); /* Function: Initializes the list to an empty state Precondition: List has been created Postcondition: List no longer exists */ ~LinkedList(); /* Function: Deletes all the items in the list Precondition: List has been declared Postcondition: List no longer exists */ private: struct node { ItemType info; node* next; }; node* head; int size;}; //========================= Implementation ================================// template <class ItemType>LinkedList<ItemType>::LinkedList(){ head = NULL; size = 0;}// end of LinkedList template <class ItemType>bool LinkedList<ItemType>::IsEmpty(){ return (head==NULL);}// end of IsEmpty template <class ItemType>void LinkedList<ItemType>::PushFront(ItemType item){ // LIFO node* temp = new node; temp-> info = item; temp-> next = head; head = temp; ++size;}// end of PushFront template <class ItemType>void LinkedList<ItemType>::PushBack(ItemType item){ // FIFO node* temp = new node; temp->info = item; temp->next = NULL; if(IsEmpty()) { head=temp; } else { node* temp2 = head; while(temp2->next!=NULL) { temp2=temp2->next; } temp2->next=temp; } ++size;}// end of PushBack template <class ItemType>ItemType LinkedList<ItemType>::PopFront(){ if(IsEmpty()) { std::cout<<"\nLIST EMPTY\n"; } else { ItemType item = head-> info; node* temp = head; head = head-> next; delete temp; --size; return item; }}// end of PopFront template <class ItemType>ItemType LinkedList<ItemType>::PopBack(){ if(IsEmpty()) { std::cout<<"\nLIST EMPTY\n"; } else if(size == 1) { ItemType item = PopFront(); return item; } else { node* temp = head; ItemType item; while(temp->next != NULL) { if(temp->next->next==NULL) { node* temp2=temp->next; temp->next=temp->next->next; item = temp2-> info; delete temp2; break; } temp=temp->next; } --size; return item; } }// end of PopBack template <class ItemType>ItemType LinkedList<ItemType>::Front(){ if(IsEmpty()) { std::cout<<"\nLIST EMPTY\n"; } else { return head-> info; }}// end of Front template <class ItemType>ItemType LinkedList<ItemType>::Back() { if(IsEmpty()) { std::cout<<"\nLIST EMPTY\n"; } else { node* temp = head; while(temp->next != NULL) { temp = temp-> next; } ItemType item = temp-> info; return item; } }// end of Back template <class ItemType>void LinkedList<ItemType>::Delete(ItemType item){ node* temp=head; if(IsEmpty()) { return; } else if(temp->info==item) { head=head->next; delete temp; --size; } else { while(temp->next!=NULL) { if(temp->next->info==item) { node* temp2=temp->next; temp->next=temp->next->next; delete temp2; --size; break; } temp=temp->next; } }}// end of Delete template <class ItemType>void LinkedList<ItemType>::Display(){ node* temp=head; while(temp!=NULL) { std::cout<<temp->info<<std::endl; temp=temp->next; }}// end of Display template <class ItemType>void LinkedList<ItemType>::Replace(ItemType initial, ItemType replace){ node* temp=head; if(IsEmpty()) { PushFront(replace); } else if(temp->info==initial) { temp->info=replace; } else { while(temp->next!=NULL) { if(temp->info==initial) { temp->info=replace; break; } temp=temp->next; } if(temp->next==NULL) { PushBack(replace); } }}// end of Replace template <class ItemType>void LinkedList<ItemType>::InsertBefore(ItemType initial, ItemType newItem){ node* temp=head; node* temp2=new node; temp2->info=initial; temp2->next=NULL; if(IsEmpty()) { PushFront(newItem); } else if(temp->info==initial) { temp->info=newItem; temp2->next=temp->next; temp->next=temp2; ++size; } else { while(temp->next!=NULL) { if(temp->info==initial) { temp->info=newItem; temp2->next=temp->next; temp->next=temp2; ++size; break; } temp=temp->next; } if(temp->next==NULL) { PushBack(newItem); } }}// end of InsertBefore template <class ItemType>void LinkedList<ItemType>::InsertAfter(ItemType initial, ItemType newItem){ node* temp=head; node* temp2=new node; temp2->info=newItem; temp2->next=NULL; if(IsEmpty()) { PushFront(newItem); } else if(temp->info==initial) { temp2->next=temp->next; temp->next=temp2; ++size; } else { while(temp->next!=NULL) { if(temp->info==initial) { temp2->next=temp->next; temp->next=temp2; ++size; break; } temp=temp->next; } if(temp->next==NULL) { PushBack(newItem); } }}// end of InsertAfter template <class ItemType>void LinkedList<ItemType>::InsertInOrder(ItemType item){ if(IsEmpty()) { PushFront(item); } else { node* temp=head; node* temp2=new node; if(item <=(temp->info)) { ItemType placeHolder=temp->info; temp2->info=placeHolder; temp->info=item; temp2->next=temp->next; temp->next=temp2; ++size; } else { while(temp->next!=NULL) { if(((temp->info) <= item) && (item <= (temp->next->info))) { temp2->info=item; temp2->next=temp->next; temp->next=temp2; ++size; return; } temp=temp->next; } if(temp->next==NULL) { PushBack(item); } } }}// end of InsertInOrder template <class ItemType>int LinkedList<ItemType>::Size(){ if(IsEmpty()) { std::cout<<"\nLIST EMPTY\n"; } return size;}// end of Size template <class ItemType>void LinkedList<ItemType>::MakeEmpty(){ if(!IsEmpty()) { std::cout << "\nDestroying nodes...\n"; while(!IsEmpty()) { node* temp = head; //std::cout << temp-> info << '\n'; head = head-> next; delete temp; } size = 0; }}// end of MakeEmpty template <class ItemType>LinkedList<ItemType>::~LinkedList(){ MakeEmpty();}// http://programmingnotes.org/
===== DEMONSTRATION HOW TO USE =====
Use of the above template class is the same as its STL counterpart. Here is a sample program demonstrating its use.
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#include <iostream>#include <string>#include "LinkedList.h"using namespace std; int main(){ // declare variables, using a string as // the item type for the class. // NOTE: you can also use an int, float, double etc. // instead of a string LinkedList<string> list; // demontrate the "InOrder" function cout<<"** These are names of fruits sorted in order" <<" using the 'InsertInOrder()' function:\n\n"; list.InsertInOrder("Tomato"); list.InsertInOrder("Orange"); list.InsertInOrder("Apple"); list.InsertInOrder("Plum"); list.Display(); cout<<"\nThere is currently "<<list.Size()<<" items in the list\n\n"; // demonstrate the "Delete" function cout<<"\n** Here is the same list with the word 'Plum' deleted" << "\nusing the 'Delete()' function:\n\n"; list.Delete("Plum"); list.Display(); cout<<"\nThere is currently "<<list.Size()<<" items in the listnn"; // demonstrate the "InsertAfter" function cout<<"\n** Now the word 'Bike' will be added to the list," <<"\nright after the word 'Apple' using the " <<"'InsertAfter()' function:\n\n"; list.InsertAfter("Apple","Bike"); list.Display(); cout<<"\nThere is currently "<<list.Size()<<" items in the list\n\n"; // demonstrate the "InsertBefore" function cout<<"\n** Now the name 'Jessica' will be added to the list," <<"\nright before the word 'Orange' using the " <<"'InsertBefore()' function:\n\n"; list.InsertBefore("Orange","Jessica"); list.Display(); cout<<"\nThere is currently "<<list.Size()<<" items in the list\n\n"; // demonstrate the "Replace" function cout<<"\n** The word 'Orange' will now be replaced with the name," <<"\n'Kat' using the 'Replace()' function:\n\n"; list.Replace("Orange","Kat"); list.Display(); cout<<"\nThere is currently "<<list.Size()<<" items in the list\n\n";}// http://programmingnotes.org/
Once compiled, you should get this as your output
** These are names of fruits sorted in order using the 'InsertInOrder()' function:
Apple
Orange
Plum
TomatoThere is currently 4 items in the list
** Here is the same list with the word 'Plum' deleted
using the 'Delete()' function:Apple
Orange
TomatoThere is currently 3 items in the list
** Now the word 'Bike' will be added to the list,
right after the word 'Apple' using the 'InsertAfter()' function:Apple
Bike
Orange
TomatoThere is currently 4 items in the list
** Now the name 'Jessica' will be added to the list,
right before the word 'Orange' using the 'InsertBefore()' function:Apple
Bike
Jessica
Orange
TomatoThere is currently 5 items in the list
** The word 'Orange' will now be replaced with the name,
'Kat' using the 'Replace()' function:Apple
Bike
Jessica
Kat
Tomato
There is currently 5 items in the list
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