How do you find the middle of a linked list? Write a C program to return the middle of a linked list

There are several methods to find the middle element in linked list, Here i have written two method which seems good.

Method-1

#include<stdio.h>
#include<ctype.h>
#include<stdlib.h>

typedef struct node
{
        int value;
        struct node *next;
        struct node *prev;
}mynode ;

void add_node(struct node **head, int value);
void print_list(char *listName, struct node *head);
void getTheMiddle(mynode *head);

// The main function..

int main()
{

        mynode *head;

        head = (struct node *)NULL;

        add_node(&head, 1);
        add_node(&head, 10);
        add_node(&head, 5);
        add_node(&head, 70);
        add_node(&head, 9);
        add_node(&head, -99);
        add_node(&head, 0);
        add_node(&head, 555);
        add_node(&head, 55);

        print_list("myList", head);

        getTheMiddle(head);

        //getch();
        return(0);
}

// This function uses one slow and one fast
// pointer to get to the middle of the LL.
// The slow pointer is advanced only by one node
// and the fast pointer is advanced by two nodes!

void getTheMiddle(mynode *head)
{

        mynode *p = head;
        mynode *q = head;

        if(q!=NULL)
        {
                while((q->next)!=NULL && (q->next->next)!=NULL)
                {
                        p=(p!=(mynode *)NULL?p->next:(mynode *)NULL);
                        q=(q!=(mynode *)NULL?q->next:(mynode *)NULL);
                        q=(q!=(mynode *)NULL?q->next:(mynode *)NULL);
                }
                printf("The middle element is [%d]",p->value);


        }

}

// Function to add a node

void add_node(struct node **head, int value)
{

        mynode *temp, *cur;

        temp = (mynode *)malloc(sizeof(mynode));
        temp->next=NULL;
        temp->prev=NULL;

        if(*head == NULL)
        {
                *head=temp;
                temp->value=value;
        }
        else
        {
                for(cur=*head;cur->next!=NULL;cur=cur->next);
                cur->next=temp; temp->prev=cur; temp->value=value;
        }
}

// Function to print the linked list...

void print_list(char *listName, struct node *head)
{
        mynode *temp;

        printf("\n[%s] -> ", listName);

        for(temp=head;temp!=NULL;temp=temp->next)
        {
                printf("[%d]->",temp->value);
        }
        printf("NULL\n");
}

***********************************************************************************

***********************************************************************************

Method-2  

#include<stdio.h>
#include<ctype.h>
#include<stdlib.h>

typedef struct node
{
int value;
struct node *next;
struct node *prev;
}mynode ;



void add_node(struct node **head, int value);
void print_list(char *listName, struct node *head);
mynode *getTheMiddle(mynode *head);

// The main function..
int main()
{
mynode *head, *middle;
head = (struct node *)NULL;

add_node(&head, 1);
add_node(&head, 10);
add_node(&head, 5);
add_node(&head, 70);
add_node(&head, 9);
add_node(&head, -99);
add_node(&head, 0);
add_node(&head, 555);
add_node(&head, 55);

print_list("myList", head);
middle = getTheMiddle(head);
printf("\nMiddle node -> [%d]\n\n", middle->value);

getch();
return(0);
}


// Function to get to the middle of the LL
mynode *getTheMiddle(mynode *head)
{
mynode *middle = (mynode *)NULL;
int i;

for(i=1; head!=(mynode *)NULL; head=head->next,i++)
{
if(i==1)
middle=head;
else if ((i%2)==1)
middle=middle->next;
}

return middle;
}


// Function to add a new node to the LL
void add_node(struct node **head, int value)
{
mynode *temp, *cur;
temp = (mynode *)malloc(sizeof(mynode));
temp->next=NULL;
temp->prev=NULL;

if(*head == NULL)
{
*head=temp;
temp->value=value;
}
else
{
for(cur=*head;cur->next!=NULL;cur=cur->next);
cur->next=temp;
temp->prev=cur;
temp->value=value;
}
}


// Function to print the LL
void print_list(char *listName, struct node *head)
{
mynode *temp;

printf("\n[%s] -> ", listName);
for(temp=head;temp!=NULL;temp=temp->next)
{
printf("[%d]->",temp->value);
}

printf("NULL\n");

}



NOTE:
In a similar way, we can find the 1/3 th node of linked list by changing (i%2==1) to (i%3==1) and in the same way we can find nth node of list by changing (i%2==1) to (i%n==1) but make sure ur (n<=i).