Why structure is used in linked list?

Linked List Program in C

A linked list is a sequence of data structures, which are connected together via links. Linked List is a sequence of links which contains items. Each link contains a connection to another link. Linked list is the second most-used data structure after array.

Implementation in C

#include #include #include #include struct node { int data; int key; struct node *next; }; struct node *head = NULL; struct node *current = NULL; //display the list void printList[] { struct node *ptr = head; printf["\n[ "]; //start from the beginning while[ptr != NULL] { printf["[%d,%d] ",ptr->key,ptr->data]; ptr = ptr->next; } printf[" ]"]; } //insert link at the first location void insertFirst[int key, int data] { //create a link struct node *link = [struct node*] malloc[sizeof[struct node]]; link->key = key; link->data = data; //point it to old first node link->next = head; //point first to new first node head = link; } //delete first item struct node* deleteFirst[] { //save reference to first link struct node *tempLink = head; //mark next to first link as first head = head->next; //return the deleted link return tempLink; } //is list empty bool isEmpty[] { return head == NULL; } int length[] { int length = 0; struct node *current; for[current = head; current != NULL; current = current->next] { length++; } return length; } //find a link with given key struct node* find[int key] { //start from the first link struct node* current = head; //if list is empty if[head == NULL] { return NULL; } //navigate through list while[current->key != key] { //if it is last node if[current->next == NULL] { return NULL; } else { //go to next link current = current->next; } } //if data found, return the current Link return current; } //delete a link with given key struct node* delete[int key] { //start from the first link struct node* current = head; struct node* previous = NULL; //if list is empty if[head == NULL] { return NULL; } //navigate through list while[current->key != key] { //if it is last node if[current->next == NULL] { return NULL; } else { //store reference to current link previous = current; //move to next link current = current->next; } } //found a match, update the link if[current == head] { //change first to point to next link head = head->next; } else { //bypass the current link previous->next = current->next; } return current; } void sort[] { int i, j, k, tempKey, tempData; struct node *current; struct node *next; int size = length[]; k = size ; for [ i = 0 ; i < size - 1 ; i++, k-- ] { current = head; next = head->next; for [ j = 1 ; j < k ; j++ ] { if [ current->data > next->data ] { tempData = current->data; current->data = next->data; next->data = tempData; tempKey = current->key; current->key = next->key; next->key = tempKey; } current = current->next; next = next->next; } } } void reverse[struct node** head_ref] { struct node* prev = NULL; struct node* current = *head_ref; struct node* next; while [current != NULL] { next = current->next; current->next = prev; prev = current; current = next; } *head_ref = prev; } void main[] { insertFirst[1,10]; insertFirst[2,20]; insertFirst[3,30]; insertFirst[4,1]; insertFirst[5,40]; insertFirst[6,56]; printf["Original List: "]; //print list printList[]; while[!isEmpty[]] { struct node *temp = deleteFirst[]; printf["\nDeleted value:"]; printf["[%d,%d] ",temp->key,temp->data]; } printf["\nList after deleting all items: "]; printList[]; insertFirst[1,10]; insertFirst[2,20]; insertFirst[3,30]; insertFirst[4,1]; insertFirst[5,40]; insertFirst[6,56]; printf["\nRestored List: "]; printList[]; printf["\n"]; struct node *foundLink = find[4]; if[foundLink != NULL] { printf["Element found: "]; printf["[%d,%d] ",foundLink->key,foundLink->data]; printf["\n"]; } else { printf["Element not found."]; } delete[4]; printf["List after deleting an item: "]; printList[]; printf["\n"]; foundLink = find[4]; if[foundLink != NULL] { printf["Element found: "]; printf["[%d,%d] ",foundLink->key,foundLink->data]; printf["\n"]; } else { printf["Element not found."]; } printf["\n"]; sort[]; printf["List after sorting the data: "]; printList[]; reverse[&head]; printf["\nList after reversing the data: "]; printList[]; }

If we compile and run the above program, it will produce the following result

Output

Original List: [ [6,56] [5,40] [4,1] [3,30] [2,20] [1,10] ] Deleted value:[6,56] Deleted value:[5,40] Deleted value:[4,1] Deleted value:[3,30] Deleted value:[2,20] Deleted value:[1,10] List after deleting all items: [ ] Restored List: [ [6,56] [5,40] [4,1] [3,30] [2,20] [1,10] ] Element found: [4,1] List after deleting an item: [ [6,56] [5,40] [3,30] [2,20] [1,10] ] Element not found. List after sorting the data: [ [1,10] [2,20] [3,30] [5,40] [6,56] ] List after reversing the data: [ [6,56] [5,40] [3,30] [2,20] [1,10] ]