printing unwanted empty line in C

Question

I am writing a program that converts strings to linked lists, and alters them, in C.

For some reason after I call my reverse function, and then print the list, it will print a new line before printing the reversed list.

for example, say my 'list' contains... a->p->p->l->e->NULL

in main() if i call... print(list); print(list);

my output:

apple
apple

BUT, in main() if i call... print(list); list=reverse(list); print(list);

my output:

apple 
/*empty line*/ 
elppa

here is my rev()

node *rev(node *head){

    node *r_head = NULL;
    while (head) {
        node *next = head->next;
        head->next = rev_head;
        r_head = head;
        head = next;
    }

    return r_head;
}

Answer 1

It seems like you're reversing the list a little too well; the NULL at the end of your list is becoming the new head, which is creating that empty space you were concerned about.

To fix it, I would suggest checking if head->next is NULL inside your while loop:

node *rev(node *head){

    node *r_head = NULL;
    while (head->next) {
        node *next = head->next;
        head->next = rev_head;
        r_head = head;
        head = next;
    }
    r_head = head;

    return r_head;
}

This code has not been tested, but I believe it should work.

Answer 2

If you have a carriage return in your string right before your NULL character, it will take the place of the first character, hence starting the second string with an additional return.

As a suggestion, take your carriage return outside of the string.

Answer 3

Although your question left out all the details, my ESP tells me that you used some variant of gets for your input function, which also captures the newline:

gets() ==> "A P P L E [newline]"

Then when you reversed it, you ended up with

"[newline] E L P P A"

And when you printed out the original string and new string back to back, you got:

"A P P L E [NL] [NL] E L P P A"

And, if you had attached a debugger and stepped through your code, like all developers should, you would already have the answer!