Question

C++

Modify this to use a separate Boolean member to keep track of whether the queue is empty rather than require that one array position remain empty.

#include <stdio.h>

#include <stdlib.h>

#include <limits.h>

// A structure to represent a queue

struct Queue

{

int front, rear, size;

unsigned capacity;

int* array;

};

// function to create a queue of given capacity.

// It initializes size of queue as 0

struct Queue* createQueue(unsigned capacity)

{

struct Queue* queue = (struct Queue*) malloc(sizeof(struct Queue));

queue->capacity = capacity;

queue->front = queue->size = 0;

queue->rear = capacity - 1; // This is important, see the enqueue

queue->array = (int*) malloc(queue->capacity * sizeof(int));

return queue;

}

// Queue is full when size becomes equal to the capacity

int isFull(struct Queue* queue)

{ return (queue->size == queue->capacity); }

// Queue is empty when size is 0

int isEmpty(struct Queue* queue)

{ return (queue->size == 0); }

// Function to add an item to the queue.

// It changes rear and size

void enqueue(struct Queue* queue, int item)

{

if (isFull(queue))

return;

queue->rear = (queue->rear + 1)%queue->capacity;

queue->array[queue->rear] = item;

queue->size = queue->size + 1;

printf("%d enqueued to queue\n", item);

}

// Function to remove an item from queue.

// It changes front and size

int dequeue(struct Queue* queue)

{

if (isEmpty(queue))

return INT_MIN;

int item = queue->array[queue->front];

queue->front = (queue->front + 1)%queue->capacity;

queue->size = queue->size - 1;

return item;

}

// Function to get front of queue

int front(struct Queue* queue)

{

if (isEmpty(queue))

return INT_MIN;

return queue->array[queue->front];

}

// Function to get rear of queue

int rear(struct Queue* queue)

{

if (isEmpty(queue))

return INT_MIN;

return queue->array[queue->rear];

}

// Driver program to test above functions./

int main()

{

struct Queue* queue = createQueue(1000);

enqueue(queue, 210);

enqueue(queue, 111);

enqueue(queue, 121);

enqueue(queue, 122);

enqueue(queue, 134);

enqueue(queue, 144);

printf("%d dequeued from queue\n\n", dequeue(queue));

printf("Front item is %d\n", front(queue));

printf("Rear item is %d\n", rear(queue));

return 0;

}

Answer 1

Solution:

Code implmenetation:

#include <stdio.h>

#include <stdlib.h>
#include<stdbool.h> // #include for bool type.
#include <limits.h>

// A structure to represent a queue

struct Queue

{

int front, rear, size;

unsigned capacity;

int* array;

};

// function to create a queue of given capacity.

// It initializes size of queue as 0

struct Queue* createQueue(unsigned capacity)

{

struct Queue* queue = (struct Queue*) malloc(sizeof(struct Queue));

queue->capacity = capacity;

queue->front = queue->size = 0;

queue->rear = capacity - 1; // This is important, see the enqueue

queue->array = (int*) malloc(queue->capacity * sizeof(int));

return queue;

}

// Queue is full when size becomes equal to the capacity

int isFull(struct Queue* queue)

{ return (queue->size == queue->capacity); }

// Queue is empty when size is 0
// isEmpty() function of boolean type returns true if queue is empty else false.
bool isEmpty(struct Queue* queue)

{
if(queue->front<0 || queue->front > queue->rear)
return true; // returns true.
else
return false; // returns false.
  
}

// Function to add an item to the queue.

// It changes rear and size

void enqueue(struct Queue* queue, int item)

{

if (isFull(queue))

return;

queue->rear = (queue->rear + 1)%queue->capacity;

queue->array[queue->rear] = item;

queue->size = queue->size + 1;

printf("%d enqueued to queue\n", item);

}

// Function to remove an item from queue.

// It changes front and size

int dequeue(struct Queue* queue)

{

if (isEmpty(queue))

return INT_MIN;

int item = queue->array[queue->front];

queue->front = (queue->front + 1)%queue->capacity;

queue->size = queue->size - 1;

return item;

}

// Function to get front of queue

int front(struct Queue* queue)

{

if (isEmpty(queue))

return INT_MIN;

return queue->array[queue->front];

}

// Function to get rear of queue

int rear(struct Queue* queue)

{

if (isEmpty(queue))

return INT_MIN;

return queue->array[queue->rear];

}

// Driver program to test above functions./

int main()

{

struct Queue* queue = createQueue(1000);

enqueue(queue, 210);

enqueue(queue, 111);

enqueue(queue, 121);

enqueue(queue, 122);

enqueue(queue, 134);

enqueue(queue, 144);

printf("%d dequeued from queue\n\n", dequeue(queue));

printf("Front item is %d\n", front(queue));

printf("Rear item is %d\n", rear(queue));

return 0;

}

Code screenshot:

Code output screenshot: