Program to reverse a linked list
 
 

/*  Program to reverse a linked list */


#include <stdio.h>
#include <conio.h>
#include <alloc.h>

/* structure containing a data part and link part */
struct node
{
    int data ;
    struct node *link ;
} ;

void addatbeg ( struct node **, int ) ;
void reverse ( struct node ** ) ;
void display ( struct node * ) ;
int count ( struct node * ) ;

void main( )
{
    struct node *p ;
    p = NULL ;  /* empty linked list */

    addatbeg ( &p, 7 ) ;
    addatbeg ( &p, 43 ) ;
    addatbeg ( &p, 17 ) ;
    addatbeg ( &p, 3 ) ;
    addatbeg ( &p, 23 ) ;
    addatbeg ( &p, 5 ) ;

    clrscr( ) ;
    display ( p ) ;
    printf ( "\nNo. of elements in the linked list = %d", count ( p ) ) ;

    reverse ( &p ) ;
    display ( p ) ;
    printf ( "\nNo. of elements in the linked list = %d", count ( p ) ) ;
}

/* adds a new node at the beginning of the linked list */
void addatbeg ( struct node **q, int num )
{
    struct node *temp ;

    /* add new node */
    temp = malloc ( sizeof ( struct node ) ) ;
    temp -> data = num ;
    temp -> link = *q ;
    *q = temp ;
}

void reverse ( struct node **x )
{
    struct node *q, *r, *s ;

    q = *x ;
    r = NULL ;

    /* traverse the entire linked list */
    while ( q != NULL )
    {
        s = r ;
        r = q ;
        q = q -> link ;
        r -> link = s ;
    }

    *x = r ;
}

/* displays the contents of the linked list */
void display ( struct node *q )
{
    printf ( "\n" ) ;

    /* traverse the entire linked list */
    while ( q != NULL )
    {
        printf ( "%d ", q -> data ) ;
        q = q -> link ;
    }
}

/* counts the number of nodes present in the linked list */
int count ( struct node * q )
{
    int c = 0 ;

    /* traverse the entire linked list */
    while ( q != NULL )
    {
        q = q -> link ;
        c++ ;
    }
    return c ;
}