Project 1 - Creation of user defined data type to implement the user interfaces for working with ‘Set’ (Mathematical Set theory)

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

struct node
{
int num;
struct node *next;
};

void create(struct node **);
void findunion(struct node *, struct node *, struct node **);
void findintersect(struct node *, struct node *, struct node **);
void display(struct node *);
void release(struct node **);

int main()
{
struct node *phead, *qhead, *intersect, *unionlist;

phead = qhead = intersect = unionlist = NULL;
printf("Enter elements in the list 1\n");
create(&phead);
printf("\nEnter elements in the list 2\n");
create(&qhead);
findunion(phead, qhead, &unionlist);
findintersect(phead, qhead, &intersect);
printf("\nDisplaying list 1:\n");
display(phead);
printf("Displaying list 2:\n");
display(qhead);
printf("Displaying the union of the 2 lists:\n");
display(unionlist);
printf("Displaying the intersection of the 2 lists:\n");
if (intersect == NULL)
{
printf("Null\n");
}
else
{
display(intersect);
}
release(&phead);
release(&qhead);
release(&unionlist);
release(&intersect);

return 0;
}

void findintersect(struct node *p, struct node *q, struct node **intersect)
{
struct node *ptemp, *qtemp, *itemp, *irear, *ifront;

ptemp = p;
while (ptemp != NULL)
{
qtemp = q;
ifront = *intersect;
while (qtemp != NULL && ptemp->num != qtemp->num)
{
qtemp = qtemp->next;
}
if (qtemp != NULL)
{
if (ifront != NULL)
{
if (ifront->num == qtemp->num)
{
ptemp = ptemp->next;
continue;
}
ifront = ifront->next;
}
itemp = (struct node *)malloc(sizeof(struct node));
itemp->num = qtemp->num;
itemp->next = NULL;
if (*intersect == NULL)
{
*intersect = itemp;
}
else
{
irear->next = itemp;
}
irear = itemp;
}
ptemp = ptemp->next;
}
}

void findunion(struct node *p, struct node *q, struct node **unionlist)
{
struct node *utemp, *ufront, *urear;
int flag = 0;

while (p != NULL)
{
ufront = *unionlist;
while (ufront != NULL)
{
if (ufront->num == p->num)
{
flag = 1;
}
ufront = ufront->next;
}
if (flag)
{
flag = 0;
}
else
{
utemp = (struct node *)malloc(sizeof(struct node));
utemp->num = p->num;
utemp->next = NULL;
if (*unionlist == NULL)
{
*unionlist = utemp;
}
else
{
urear->next = utemp;
}
urear = utemp;
}
p = p->next;
}
while (q != NULL)
{
ufront = *unionlist;
while (ufront != NULL)
{
if (ufront->num == q->num)
{
flag = 1;
}
ufront = ufront->next;
}
if (flag)
{
flag = 0;
}
else
{
utemp = (struct node *)malloc(sizeof(struct node));
utemp->num = q->num;
utemp->next = NULL;
if (*unionlist == NULL)
{
*unionlist = utemp;
}
else
{
urear->next = utemp;
}
urear = utemp;
}
q = q->next;
}
}

void create(struct node **head)
{
struct node *temp, *rear;
int ch, a;

do
{
printf("Enter a number: ");
scanf("%d", &a);
temp = (struct node *)malloc(sizeof(struct node));
temp->num = a;
temp->next = NULL;
if (*head == NULL)
{
*head = temp;
}
else
{
rear->next = temp;
}
rear = temp;
printf("Do you want to continue [1/0] ? ");
scanf("%d", &ch);
} while (ch != 0);
}

void display(struct node *head)
{
while (head != NULL)
{
printf("%d ", head->num);
head = head->next;
}
printf("\n");
}

void release(struct node **head)
{
struct node *temp = *head;
while ((*head) != NULL)
{
(*head) = (*head)->next;
free (temp);
temp = *head;
}
}