queue.c

queue.c

contents ::

  app.c
  graph.c
  graph.h
  mylib.c
  mylib.h
  queue.c
  queue.h

#include <stdio.h>
#include <stdlib.h>
#include "mylib.h"
#include "queue.h"
#include "graph.h"

/* The queue structure */
struct queue_c {
  int *the_q;
  int front;
  int end;
  int size;
};
//static int size = 0;

/* creates a new queue */
queue queue_new(int size){
  queue q = emalloc(sizeof *q);
  q->the_q = emalloc(size * sizeof q->the_q[0]);
  q->size=size;
  q->front=0;
  q->end=0;
  return q;
}

/*
  returns the size of the queue
  this should be the number of items
  actually in the queue
*/

int queue_size(queue q){
  return q->end - q->front;
}

/*
  inserts an item onto the queue
  if there is room returns 1 for "all good"
  if the queue is full returns 0
  for "all is not so good"
*/
void queue_enqueue(queue q, int i){
  if(queue_size(q)<q->size){
    q->the_q[q->end%q->size]=i;
    q->end++;
    // return 1;
  } else {
    printf("Sorry queue full\n");
    // return 0;
  }
}

/*
  returns the item at the front of the queue
  if there is an item to return it returns it,
  if there is not then it returns -1
  ********************************************
  returning -1 is ok for the implementation of the
  graph but if we want to put something onto the
  stack that could possibly return -1, then we will
  have to exit the program if there is nothing on
  the queue to return, else make sure that error
  checking is preformed before this is called.
*/
int queue_dequeue(queue q){
  if(queue_size(q)>0){
    int value = q->the_q[q->front%q->size];
    q->front++;
    return value;
  } else {
    printf("Sorry queue empty\n");
    return -1; /* I don't really feel -1 is satisfacory value to return */
  }
}

James Little