C Program to Reverse the Linked List

How to reverse the linked list?

Linked list are not stored in adjacent locations and array occupy continuous locations.

Printing nodes from tail to head pointer.

C Program to Reverse the Linked List

#include<stdio.h>  

//structure contains data and link
struct node
{
    int data;
    struct node *link;
};

void append(struct node **head, int data)
{
    struct node *temp, *tail;
    temp = *head;

    // if linked list is empty, adding as first node.
    if(*head == NULL)
    {
        temp = malloc( sizeof (struct node));
        temp->data = data;
        temp->link = NULL;
        *head = temp;
    }
    // adding in the last if linked list is not empty
    else
    {
        //Move to last node
        while(temp->link != NULL)
        {
            temp = temp->link;
        }
        tail = malloc( sizeof (struct node));
        tail->data = data;
        tail->link = NULL;
        temp->link = tail;
    }
    
}

// displays the linked list from head to tail nodes
void display(struct node *head)
{
    printf("\n");
    // traversing entire linked list
    printf("\nhead==>");
    while(head != NULL)
    {
        printf("%d-->", head->data);
        head = head->link;
    }
    printf("tail");
}

// finds the number of nodes added in the linked list.
int count(struct node *head)
{
    int c = 0;
    while(head != NULL)                                                         
    {                                                                           
        head = head->link;          
        c++;
    } 
    return c;
}

// deletes the linked list elements
int delete(struct node **head, int data)
{
    struct node *old, *temp;
    temp = *head;

    while(temp != NULL)
    {
        if(temp->data == data)
        {
            // deleting first node if data matches
            if(temp == *head)
            {
                *head = temp->link;
                free(temp);
                return 1;
            }
            // deleting other nodes except first node
            else
            {
                old->link = temp->link;
                free(temp);
                return 1;
            }
        }
        // old points to the previous node
        old = temp;
        temp = temp->link;
    }
    return 0;
}

// reverses the linked list from tail to head nodes
void reverse(struct node **head)
{
    struct node *temp1, *temp2, *temp3;
    temp1 = *head;
    temp2 = NULL;

    while(temp1!=NULL)
    {
        temp3 = temp2;
        temp2 = temp1;
        temp1 = temp1->link;
        temp2->link = temp3;
    }
    *head = temp2;
}


void main()                                                                     
{       
    int op, data, loc;                                                                        
    struct node *ptr;                                                           
    // Empty linked list                                                        
    ptr = NULL;                                                                 
                                                                                
    printf("\nNumber of elements in the linked list: %d", count(ptr));          
    append(&ptr, 1);                                                            
    append(&ptr, 2);                                                            
    append(&ptr, 3);                                                            
                                                                                
    display(ptr);       
    printf("\nNumber of elements in the linked list: %d", count(ptr));

    do
    {
        printf("\nLinked List\n---------------\n1.Add element in end\n2.reverse\n3.delete\n4.display\n5.count\n0.exit");
        printf("\nEnter choice: ");
        scanf("%d", &op);
        switch(op)
        {
            case 1:
                printf("\nEnter element: ");                                    
                scanf("%d", &data);                                             
                append(&ptr, data);  
                break;
            case 2:
                printf("\nReverse linked list: ");
                reverse(&ptr);
                break;
                
            case 3:
                printf("\nEnter element: ");                                    
                scanf("%d", &data);                                             
                delete(&ptr, data);  
                break;
            case 4:
                display(ptr);
                break;
            case 5:
                printf("\nNumber of elements in the linked list: %d", count(ptr));
                break;
        }
    }while(op>=1 && op<=4);
}       
                                                                                                                                                                                                                                                                                                                                                                                                           

$ cc reverse-linked-list.c 
reverse-linked-list.c: In function ‘append’:
reverse-linked-list.c:18:16: warning: implicit declaration of function ‘malloc’ [-Wimplicit-function-declaration]
         temp = malloc( sizeof (struct node));
                ^~~~~~
reverse-linked-list.c:18:16: warning: incompatible implicit declaration of built-in function ‘malloc’
reverse-linked-list.c:18:16: note: include ‘’ or provide a declaration of ‘malloc’
reverse-linked-list.c:31:16: warning: incompatible implicit declaration of built-in function ‘malloc’
         tail = malloc( sizeof (struct node));
                ^~~~~~
reverse-linked-list.c:31:16: note: include ‘’ or provide a declaration of ‘malloc’
reverse-linked-list.c: In function ‘delete’:
reverse-linked-list.c:76:17: warning: implicit declaration of function ‘free’ [-Wimplicit-function-declaration]
                 free(temp);
                 ^~~~
reverse-linked-list.c:76:17: warning: incompatible implicit declaration of built-in function ‘free’
reverse-linked-list.c:76:17: note: include ‘’ or provide a declaration of ‘free’
reverse-linked-list.c:83:17: warning: incompatible implicit declaration of built-in function ‘free’
                 free(temp);
                 ^~~~
reverse-linked-list.c:83:17: note: include ‘’ or provide a declaration of ‘free’

$ ./a.out 

Number of elements in the linked list: 0

head==>1-->2-->3-->tail
Number of elements in the linked list: 3
Linked List
---------------
1.Add element in end
2.reverse
3.delete
4.display
5.count
0.exit
Enter choice: 1

Enter element: 4

Linked List
---------------
1.Add element in end
2.reverse
3.delete
4.display
5.count
0.exit
Enter choice: 4


head==>1-->2-->3-->4-->tail
Linked List
---------------
1.Add element in end
2.reverse
3.delete
4.display
5.count
0.exit
Enter choice: 2

Reverse linked list
Linked List
---------------
1.Add element in end
2.reverse
3.delete
4.display
5.count
0.exit
Enter choice: 4


head==>4-->3-->2-->1-->tail
Linked List
---------------
1.Add element in end
2.reverse
3.delete
4.display
5.count
0.exit
Enter choice: 5

Number of elements in the linked list: 4
Linked List
---------------
1.Add element in end
2.reverse
3.delete
4.display
5.count
0.exit
Enter choice: 2

Reverse linked list
Linked List
---------------
1.Add element in end
2.reverse
3.delete
4.display
5.count
0.exit
Enter choice: 4


head==>1-->2-->3-->4-->tail
Linked List
---------------
1.Add element in end
2.reverse
3.delete
4.display
5.count
0.exit
Enter choice: 0