front and rear pointers of circular queue are exceeding the size of array which can be seen in the print statement the input given for size was 3 where pointers go till the value 4 and 6.It would be helpful if someone could point out where I am going wrong. The input on which I tested was 20 (size of number ), 3(size of queue) ,7 0 1 2 0 3 0 4 2 3 0 3 2 1 2 0 1 7 0 1 (numbers) . output should be page fault - 15 and hit - 5 but it was 9 and 11.

#include<stdio.h>
#include<math.h>
#include<stdlib.h>

struct queue{
    int size;
    int f;
    int r;
    int *arr;
};

int isEmpty(struct queue *q)
{
    if(q->f == -1 || q->r == -1)
    {
        return 1;
    }
    return 0;  
}

int isFull(struct queue *q)
{
    if(q->r == q->f-1 || (q->f == 0 && q->r == q->size - 1))
    {
        return 1;
    }
    return 0;  
}

void enqueue(struct queue *q ,int data)
{
    // if(isFull(q))
    // {
    //     printf("Queue Overflow\n");
    //     return;
    // }
    if(isEmpty(q))
    {
        q->f=0;
        q->r=0;
    }
    else if(q->r == q->size-1 && q->f !=0)
    {
        q->r = 0;
    }
    else
    {
        q->r = q->r   1;
    }
    q->arr[q->r] = data;
    // printf("%d\n",q->arr[q->r]);
}

void dequeue(struct queue *q)
{
    // int val = -1;

    // if(isEmpty(q))
    // {
    //     printf("Queue Underflow\n");
    //     return val;
    // }

    // val = q->arr[q->f];

    if(q->r == q->f)
    {
        q->f = -1;
        q->r = -1;
    }
    else if(q->f == q->size-1)
    {
        q->f = 0;
    }
    else
    {        
        q->f = q->f   1;
    }    
    // return val;
}

int isPresent(struct queue *q ,int data)
{
    for(int i=q->f;i!=q->r;i  )
    {
        if(i == q->size-1)
        {
            if(data == q->arr[i])
            {
                return 1;
            }
            i = -1;
            continue;
        }
        if(data == q->arr[i])
        {
            return 1;
        }
    }
    if(data == q->arr[q->r])
    {
        return 1;
    }

    return 0;
}

int main(void)
{
    int m,n;
    int hit=0,miss=0;
    struct queue *q;
    q->f = -1;
    q->r = -1;

    printf("Enter the amount of numbers:\n");
    scanf("%d",&n);
 
    printf("Enter the Frame no.:\n");
    scanf("%d",&m);
    
    int num[n];
    q->size = m;
    q->arr = (int *)malloc(q->size*sizeof(int));
    
    
    printf("Enter the numbers:\n");
    for(int i=0;i<n;i  )
    {
        scanf("%d",&num[i]);
    }
    
    
    for(int i=0;i<n;i  )
    {
        printf("\n%d\n",q->f);
        printf("%d\n",q->r);
        if(!isFull(q))
        {
            enqueue(q,num[i]);
            // miss  ;
        }
        else if(isPresent(q,num[i]))
        {
            hit  ;
        }
        else
        {
            dequeue(q);
            enqueue(q,num[i]);
            miss  ;
        }
    }

    printf("Page Fault:%d\n",miss);
    printf("Hit:%d\n",hit);
    return 0;
}

CodePudding user response：

Compiling the code in the question with warnings enabled reveals that q is used uninitialized in line 113, q->f = -1;. In the prior line, struct queue *q;, q is defined but not given any value. Because of this, the behavior of the program is not defined by the C standard, and there is no reason the “output should be page fault.“

You must initialize q by setting it to point to suitable memory, perhaps allocated with malloc, or otherwise redesign your program so that q is not used before it is initialized.

Enable warnings in your compiler and elevate warnings to errors. With Clang, start with -Wmost -Werror. With GCC, start with -Wall -Werror. With MSVC, start with /W3 /WX.