C Programming Code Examples
C > Linked Lists Code Examples
Program to Implement Doubly Linked List using Singly Linked List
/* Program to Implement Doubly Linked List using Singly Linked List
This C Program implements doubly linked list using singly linked list. It makes use of 2 pointers, one points at the current node, other points at the head. When user requests to move back, the pointer from head travels to a previous node of the current pointer. The pointer to previous node is the resulting node. */
#include <stdio.h>
#include <stdlib.h>
struct node
{
int j;
struct node *next;
};
void create(struct node **);
void move (struct node *);
void release(struct node **);
void display(struct node *);
int main()
{
struct node *p = NULL, *q = NULL;
int result, count;
printf("Enter data into the list\n");
create(&p);
printf("Displaying list:\n");
display(p);
move(p);
release (&p);
return 0;
}
void move(struct node *head)
{
struct node *p, *q;
int ch;
p = q = head;
printf("\nPointer at %d\n", head->j);
do
{
printf("Select option:\n1. Move front\n2. Move back\n3. Exit\nYour choice: ");
scanf("%d", &ch);
switch(ch)
{
case 1: if(q->next != NULL)
{
q = q->next;
printf("\nPointer at %d\n", q->j);
}
else
{
printf("\nPointer at last node %d. Cannot move ahead.\n", q->j);
}
break;
case 2: while (p->next != q)
{
p = p->next;
}
if (p == q)
{
printf("\nPointer at first node %d. Cannot move behind.\n", q->j);
}
else
{
q = p;
p = head;
printf("\nPointer at %d\n", q->j);
}
break;
case 3: return;
default: printf("\nInvalid choice entered. Try again\n");
}
} while (1);
}
void create(struct node **head)
{
int c, ch;
struct node *temp, *rear;
do
{
printf("Enter number: ");
scanf("%d", &c);
temp = (struct node *)malloc(sizeof(struct node));
temp->j = c;
temp->next = NULL;
if (*head == NULL)
{
*head = temp;
}
else
{
rear->next = temp;
}
rear = temp;
printf("Do you wish to continue [1/0]: ");
scanf("%d", &ch);
} while (ch != 0);
printf("\n");
}
void display(struct node *head)
{
while (head != NULL)
{
printf("%d\t", head->j);
head = head->next;
}
printf("\n");
}
void release(struct node **head)
{
struct node *temp;
while ((*head) != NULL)
{
temp = *head;
(*head) = (*head)->next;
free(temp);
}
}
Pointers in C are easy and fun to learn. Some C programming tasks are performed more easily with pointers, and other tasks, such as dynamic memory allocation, cannot be performed without using pointers. So it becomes necessary to learn pointers to become a perfect C programmer. Let's start learning them in simple and easy steps. As you know, every variable is a memory location and every memory location has its address defined which can be accessed using ampersand (&) operator, which denotes an address in memory. Consider the following example, which prints the address of the variables defined. A pointer is a variable whose value is the address of another variable, i.e., direct address of the memory location. Like any variable or constant, you must declare a pointer before using it to store any variable address. The general form of a pointer variable declaration is:
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The if-else statement is used to perform two operations for a single condition. The if-else statement is an extension to the if statement using which, we can perform two different operations, i.e., one is for the correctness of that condition, and the other is for the incorrectness of the condition. Here, we must notice that if and else block cannot be executed simiulteneously. Using if-else statement is always preferable since it always invokes an otherwise case with every if condition.
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