Thread: FIFO Queue

I am trying to understand queue in c language. I have gone through page Programming Concepts: Queues - Wikibooks, open books for an open world

Code:

#include<stdio.h>

#include<stdlib.h> 
    
struct Queue  
{ 
  int data;              
  struct Queue *Next;  
}; 




int main() 
{ 
  struct Node* Front = NULL; 
  
  return 0; 
}

I am planning two write two functions, enqueue to insert data into queue and dequeue to delete. I don't understand how to implement.

I would apricate for any help

Originally Posted by Salem

Code:

void queueInit(struct Queue *q);  // Initialise

.

Salem, Thank you

What function queueInit(struct Queue *q); supposed to do ?

Originally Posted by gajya

Salem, Thank you

What function queueInit(struct Queue *q); supposed to do ?

When you are seated at a table in a restaurant, what does the table look like?

That's what queueInit() does. It "sets the table." It doesn't know who is going to eat, or how many, or what they will have. It just ensures that there is a clean table, with napkins, maybe some condiments, maybe some small plates and water glasses, maybe a tablecloth, the chairs are straight and in the right position, etc.

If your queue is using an array, then there are probably some integers telling how many values are stored. At the start, queueInit would set them to zero.

If your queue is using a linked list, then there might be an integer length, which should start at zero. And there would be a "head" pointer to the first node in the linked list, which should be set to null.

If your queue is using a dictionary, then there should be an empty dictionary.

If your queue is using a file, there should be a filename, maybe a file handle or file pointer, all set up.

The point is, whatever your queue does, the queueInit() function should set it up to the "empty" state.

Originally Posted by Sir Galahad

(Setting all pointers to zero, for example.)

I think I have done

Code:

#include<stdio.h>#include<stdlib.h> 
    
struct Queue {
  int data[10];
  int front;
  int back;
};


void queueInit(struct Queue *q)  // Initialise
{
	
    q-> data[10] = 0;
	q-> front = NULL;
	q-> back = NULL;
}




int main() 
{ 
   struct Queue *q =  NULL;
   q = malloc(sizeof(*q));
  
   queueInit(q); 
   
  return 0; 
}

Originally Posted by laserlight

The idea is to pass a pointer to a struct Queue object to queueInit so that queueInit can supply the initial values which will then be reflected in the object from the caller. You don't have to use dynamic memory allocation for this, e.g., to keep things simple you could have written:

Am I doing that ?
Both pointers initially at 0

Code:

#include<stdio.h>

#include<stdlib.h> 
    
struct Queue {
  int data[10];
  int front;
  int back;
};




void queueInit(struct Queue *q)  // Initialise
{
	q->data[0] = 0; 
	q->front = 0;
    q->back = 0;	
	
}


int main() 
{ 
   struct Queue *q = NULL;


   queueInit(&q);  
   
  return 0; 
}

Originally Posted by Salem

Enqueue is
q->data[q->front++] = data;

Dequeue is
return q->data[q->back++];

I don't understand these two lines exactly what happens

Code:

#include<stdio.h>  

#include<stdlib.h> 


#define size  10
#define  True  1
       
struct Queue {
  int data[size];
  int front;
  int back;
};
  
  
void queueInit(struct Queue *q)  // Initialise
{
    q->data[0] = 0;
    q->front = 0;
    q->back = 0;     
} 
  
 int queueIsEmpty() // is it empty?
 {
     if (size < 0)
         return True; 
 }
  
  int queueIsFull()  // is it Full?
 {
     if ( size == 10)
         return True; 
 }
 
void queueEnqueue(struct Queue *q, int data)  // enqueue a value
{
    if (queueIsEmpty()== 1)
    {
        
    }

}


void queueDequeue(struct Queue *q, int *data) // dequeue a value
{
    if (queueIsFull()== 1)
    {
        
    }
}
   
int main() 
{ 
 
  struct Queue q;
  queueInit(&q); 
  queueEnqueue(&q, 1);  // enqueue a value
     
  return 0; 
}

Originally Posted by Salem

Your size is the size of the array, which is constant.

You want the number of elements presently stored in the queue.
In rather simplistic terms, this is just front - back.

sorry but still I don't have clear idea

Code:

#include<stdio.h>   
#include<stdlib.h> 
 
 
#define size  10
#define  True  1
        
struct Queue {
  int data[size];
  int front;
  int back;
};
   
   
void queueInit(struct Queue *q)  // Initialise
{
    q->data[0] = 0;
    q->front = 0;
    q->back = 0;     
} 
   
 int queueIsEmpty() // is it empty?
 {
     if (size < 0)
         return True; 
 }
   
  int queueIsFull()  // is it Full?
 {
     if ( size == 10)
         return True; 
 }
  
void queueEnqueue(struct Queue *q, int data)  // enqueue a value
{
    if (queueIsEmpty()== 1)
    {
         q->data[0] = data;
		 printf ("%d",  q->data);
		 q->front++; 
		 
    }
 
}
 
 
int main() 
{ 
  
  struct Queue q;
  queueInit(&q); 
  queueEnqueue(&q, 1);  // enqueue a value
 
  return 0; 
}