Linked List implementation of Queue.

Queue_LinkedList.c

/*Queue - Linked List implementation*/
#include<stdio.h>
#include<stdlib.h>
struct Node {
	int data;
	struct Node* next;
};
// Two glboal variables to store address of front and rear nodes. 
struct Node* front = NULL;
struct Node* rear = NULL;

// To Enqueue an integer
void Enqueue(int x) {
	struct Node* temp = 
		(struct Node*)malloc(sizeof(struct Node));
	temp->data =x; 
	temp->next = NULL;
	if(front == NULL && rear == NULL){
		front = rear = temp;
		return;
	}
	rear->next = temp;
	rear = temp;
}

// To Dequeue an integer.
void Dequeue() {
	struct Node* temp = front;
	if(front == NULL) {
		printf("Queue is Empty\n");
		return;
	}
	if(front == rear) {
		front = rear = NULL;
	}
	else {
		front = front->next;
	}
	free(temp);
}

int Front() {
	if(front == NULL) {
		printf("Queue is empty\n");
		return;
	}
	return front->data;
}

void Print() {
	struct Node* temp = front;
	while(temp != NULL) {
		printf("%d ",temp->data);
		temp = temp->next;
	}
	printf("\n");
}

int main(){
	/* Drive code to test the implementation. */
	// Printing elements in Queue after each Enqueue or Dequeue 
	Enqueue(2); Print(); 
	Enqueue(4); Print();
	Enqueue(6); Print();
	Dequeue();  Print();
	Enqueue(8); Print();
}

There is a mistake in dequeue method ..you need to do temp = temp->next;
then free(first); first = temp;
You are freeing the second element each time and if free->next is null then it will crash.

i understand your problem , but see , the case that you're mentioning is when we have only one node in the queue , and here we've explicitly considered that case which is when both front and rear are equal . In that we're deleting simply that one node , not performing
any operation involving , and after the deletion of that single node both front and rear would be pointing to NULL .
I hope i've explained it well .

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