array in circular queue not getting initialised

Question

I am having problem in the c implementation of circular queue. The enqueue operation is not working properly. The value is not getting initialised in the array.

the structure for queue is:

typedef struct
{   
    int a[5];
    int tail;
    int head;
    int cap;
 }Que;

the enqueue function:

    int enque(Que *q,int num) 
 {
    if((q->head)==(q->tail ))
        return -1;
    if(q->head==-1)
        q->head=0;
    q->a[q->tail]=num;
    (q->tail) ++;
    if(q->tail ==q->cap)
    q->tail=0;
    return 0;
}

the dequeue function:

    int deque(Que *q)
{
    if((q->head)==-1)
     return -1;

    int b= q->a[q->head];
    (q->head)++;
    if(q->head==q->cap)
        q->head=0;
    if(q->head==q->tail)
        q->head=-1;

    return b;
}

the head is position of the index to be dequeued and tail is the index where the element has to be added. The initial values of head is -1 , tail is 0 and cap is 5. These values have been set by another function.

@Klas Lindbäck Here is the complete code:

#include <stdlib.h>
#include <stdio.h>
typedef struct
{   
int a[5];
    int tail;
    int head;
    int cap;
}Que;
int deque(Que *q)
{
    if((q->head)==-1)
     return -1;

    int b= q->a[q->head];
    (q->head)++;
    if(q->head==q->cap)
        q->head=0;
    if(q->head==q->tail)
        q->head=-1;

    return b;
}
void initialize(Que *q)
{
    q->head=-1;
    q->tail=0;
    q->cap=5;
}
int enque(Que *q,int num) 
{
    if((q->head)==(q->tail ))
        return -1;
    if(q->head==-1)
        q->head=0;
    q->a[q->tail]=num;
    printf("%d \n",q->a[q->tail]);
    (q->tail) ++;
    if(q->tail ==q->cap)
    q->tail=0;
    return 0;
}
int main()
{
    Que q;
    initialize(&q);
    int i=1;
    for(;i<=5;i++)
    {
        int num;
        printf("input a number: ");
        scanf("%d",num);
        enque(&q,num);
    }
    int c=q.a[0];
    printf("%d  %d  %d\n",q.a[2],c,q.a[3]);

}

Klas Lindbäck · Accepted Answer · 2013-04-17 15:07:15Z

1

I cannot find anything wrong in your enque/deque functions. The problem lies elsewhere.

I tested your code with the following main:

int main(int argc, char**argv) {
  int var = 7456;
  Que q;
  q.head=-1; q.tail=0; q.cap=5;

  enque(&q, 12);
  enque(&q, 6);
  printf("First queue value =%d\n", deque(&q));
  return 0;
}

and the output was

First queue value =12

Edit:

Error is here:

    scanf("%d",num);

Change it to:

    scanf("%d", &num);

edited Apr 17, 2013 at 15:07

answered Apr 17, 2013 at 13:53

Klas Lindbäck

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1 Comment

Klas Lindbäck Over a year ago

Problem found. See Edit in my answer.

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