List Implementation of Queue using C program

Data Structures using C Language / List Implementation of Queue using C program

Program

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

struct node 
{
int data;
struct node * next;
};
struct node * front = NULL;
struct node * rear = NULL;

void enqueue(int value) {
struct node * ptr;
ptr = (struct node * ) malloc(sizeof(struct node));
ptr->data = value;
ptr-> next = NULL;
if ((front == NULL) && (rear == NULL)) 
front = rear = ptr;
else 
{
rear->next = ptr;
rear = ptr;
}
printf("Node Inserted\n\n");
}

int dequeue() 
{
if (front == NULL) 
{
printf("\nUnderflow\n");
return -1;
} else {
struct node * temp = front;
int temp_data = front->data;
front = front->next;
free(temp);
return temp_data;
}
}

void show() {
struct node * temp;
if ((front == NULL) && (rear == NULL)) 
printf("\nQueue is Empty\n");
else {
printf("The queue is \n");
temp = front;
while (temp) {
printf("%d--->", temp->data);
temp = temp-> next;
}
printf("NULL\n\n");
}
}

int main() {
int choice, value;
printf("\nQueue Implementation using Linked List\n");
while (choice != 4) 
{
printf("1.Enqueue\t2.Dequeue\t3.Display\t4.Exit\n");
printf("\nEnter your choice : ");
scanf("%d", & choice);
switch (choice) {
case 1:printf("\nEnter a value to insert: ");scanf("%d", & value);enqueue(value);break;
case 2:printf("Popped element is :%d\n", dequeue());break;
case 3:show();break;
case 4:exit(0);break;
default:printf("\nWrong Choice\n");
}
}
return 0;
}

Output

Queue Implementation using Linked List
1.Enqueue      2.Dequeue     3.Display         4.Exit
Enter your choice: 1
Enter a value to insert : 9
Node Inserted
1.Enqueue      2.Dequeue     3.Display         4.Exit
Enter your choice: 1
Enter a value to insert : 3
Node Inserted
1.Enqueue      2.Dequeue     3.Display         4.Exit
Enter your choice: 1
Enter a value to insert : 6
Node Inserted
1.Enqueue      2.Dequeue     3.Display         4.Exit
Enter your choice: 3
936Null.

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