deleting only non-existing node which is right next to last node in linked list terminates the program

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When I delete any node present in a linked list my code works perfectly. let's say my linked list has 10 nodes, if I want to delete 12th, 13th, 14th... nodes my program gives me the expected message.

But if I want to delete 11th node(which is adjacent to the last node), my program terminates with exit code -1073741819 (0xC0000005) 

int delete()
{
    int position, count = 1;
    printf( "\nwrite your position" );
    scanf( "%d", &position );

    struct node *p, *q;
    p = head;
    if ( position == 0 ) {
        p = p->next;
        head = p;
        return 0;
    }
    while ( p != NULL && count != position ) {
        count++;
        p = p->next;
    }
    count = 0;
    if ( p == NULL ) {
        printf( "link list is empty or link not found\n" );
        return 0;
    }
    else {
        q = p->next;
        p->next = q->next;
    }
}
c
linked-list
singly-linked-list
asked on Stack Overflow Dec 15, 2019 by taretor • edited Dec 15, 2019 by Student

2 Answers

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when i delete qny node present in a linked list my code works perfect

No, it doesn't. It looks good for deleting the node at index 0, but for any other positive index n, it attempts to delete the node at index n+1 by advancing pointer p to point to node n and then manipulating p->next.

but if i want to delete 11th node(which is adjacent to last node) ,my program terminates with exit code -1073741819 (0xC0000005)

I don't believe that, but I would believe that the program fails when you try to delete the last node (rather than one past the last). In that case, p is advanced to point to the last node, whose next pointer is null. Therefore this code:

    q=p->next;
    p->next=q->next;

sets q to a null pointer and then attempts to dereference that pointer.

answered on Stack Overflow Dec 15, 2019 by John Bollinger
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When p is NULL then this statement is not valid

p->next = q->next;

so, the solution is adding p->next == NULL statement to if condition like this:-

if ( p == NULL || p->next == NULL ) {
    printf( "link list is empty or link not found\n" );
    return 0;
}

now the correct code is 

int delete()
{
    int position, count = 1;
    printf( "\nwrite your position" );
    scanf( "%d", &position );

    struct node *p, *q;
    p = head;
    if ( position == 0 ) {
        p = p->next;
        head = p;
        return 0;
    }
    while ( p != NULL && count != position ) {
        count++;
        p = p->next;
    }
    count = 0;
    if ( p == NULL || p->next == NULL ) {
        printf( "link list is empty or link not found\n" );
        return 0;
    }
    else {
        q = p->next;
        p->next = q->next;
    }
}
answered on Stack Overflow Dec 15, 2019 by taretor • edited Dec 15, 2019 by Student

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