Reputation: 384

I'm having trouble figuring out the difference between these two blocks of code

Alright, this is a really quick question: why does this first block of code compile, but the second one doesn't? They seem like they should be equivalent, since all that I change is the variable declaration/references.

First:

int memberStudents(struct studentType x, Snodeptr students, Snodeptr *s) {
    Snodeptr p = *s;

    while (p->next != NULL) {
        if (strcmp(x.sid, p->student.sid) == 0)
            return 1;

        p = p->next;
    }

    return 0;
}

Second:

int memberStudents(struct studentType x, Snodeptr students, Snodeptr *s) {
    while (s->next != NULL) {
        if (strcmp(x.sid, s->student.sid) == 0)
            return 1;

            s = s->next;
    }

    return 0;
}

I want to change the Snodeptr s so that it points to the proper place, but when I try the second block of code I get an error saying there is a request for member 'next' in something not a struct or union.

Upvotes: 1

Answers (4)

simonc

Reputation: 42165

In the first block, the while loop operates on a Snodeptr instance. In the second block you're operating on a Snodeptr*.

Upvotes: 2

Happy Green Kid Naps

Reputation: 1673

I expect this (slightly modified version of your second snippet) should compile:

int memberStudents(struct studentType x, Snodeptr students, Snodeptr *s) {
    while ((*s)->next != NULL) {
        if (strcmp(x.sid, (*s)->student.sid) == 0)
            return 1;

            (*s) = (*s)->next;
    }
    return 0;
}

Upvotes: 1