C Program to Segregate Even and Odd Nodes in a Linked List

This C Program modifies the linked list such that all even numbers appear before all the odd number in the modified linked list.

Here is a source code of the C program that modifies the linked list such that all even numbers appear before all the odd number. The C program is successfully compiled and run on a Linux system. The program output is also shown below.

```
/*
```

 * C Program to Modify the Linked List such that All Even Numbers

 * appear before all the Odd Numbers in the Modified Linked List

```
 */
```
```
#include <stdio.h>
```
```
#include <stdlib.h>
```
```
 
```
```
struct node
```
```
{
```
```
    int num;
```
```
    struct node *next;
```
```
};
```
```
 
```
```
void create(struct node **);
```

void generate_evenodd(struct node *, struct node**);

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void release(struct node **);
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void display(struct node *);
```
```
 
```
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int main()
```
```
{
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```
    struct node *p = NULL, *q = NULL;
```
```
    int key, result;
```
```
 
```

    printf("Enter data into the list\n");

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    create(&p);
```

    printf("Displaying the nodes in the list:\n");

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    display(p);
```
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    generate_evenodd(p, &q);
```

    printf("Displaying the list with even and then odd:\n");

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    display(q);
```
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    release(&p);
```
```
 
```
```
    return 0;
```
```
}
```
```
 
```

void generate_evenodd(struct node *list, struct node **head)

```
{
```

    struct node *even = NULL, *odd = NULL, *temp;

```
    struct node *reven, *rodd;
```
```
    while (list != NULL)
```
```
    {
```

        temp = (struct node *)malloc(sizeof(struct node));

```
        temp->num = list->num;
```
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        temp->next = NULL;
```
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        if (list->num % 2 == 0)
```
```
        {
```
```
            if (even == NULL)
```
```
            {
```
```
                even = temp;
```
```
            }
```
```
            else
```
```
            {
```
```
                reven->next = temp;
```
```
            }
```
```
            reven = temp;
```
```
        }
```
```
        else
```
```
        {
```
```
            if (odd == NULL)
```
```
            {
```
```
                odd = temp;
```
```
            }
```
```
            else
```
```
            {
```
```
                rodd->next = temp;
```
```
            }
```
```
            rodd = temp;
```
```
        }
```
```
        list = list->next;
```
```
    }
```
```
    reven->next = odd;
```
```
    *head = even;
```
```
}
```
```
 
```
```
void create(struct node **head)
```
```
{
```
```
    int c, ch;
```
```
    struct node *temp, *rear;
```
```
 
```
```
    do
```
```
    {
```
```
        printf("Enter number: ");
```
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        scanf("%d", &c);
```

        temp = (struct node *)malloc(sizeof(struct node));

```
        temp->num = 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 *p)
```
```
{
```
```
    while (p != NULL)
```
```
    {
```
```
        printf("%d\t", p->num);
```
```
        p = p->next;
```
```
    }
```
```
    printf("\n");
```
```
}
```
```
 
```
```
void release(struct node **head)
```
```
{
```
```
    struct node *temp = *head;
```
```
    *head = (*head)->next;
```
```
    while ((*head) != NULL)
```
```
    {
```
```
        free(temp);
```
```
        temp = *head;
```
```
        (*head) = (*head)->next;
```
```
    }
```
```
}
```

$ gcc evenodd.c 
$ ./a.out
Enter data into the list
Enter number: 1
Do you wish to continue [1/0]: 1
Enter number: 2
Do you wish to continue [1/0]: 1
Enter number: 3
Do you wish to continue [1/0]: 1
Enter number: 4
Do you wish to continue [1/0]: 1
Enter number: 5
Do you wish to continue [1/0]: 1
Enter number: 6
Do you wish to continue [1/0]: 0
 
Displaying the nodes in the list:
1	2	3	4	5	6	
Displaying the list with even and then odd:
2	4	6	1	3	5