Linked list[solved]

Question

Push element at head
I wrap my head around this problem since quite a long time but I can't seem to find how to do it: I want to make a VOID function that adds a element at the front of the list. I got a code here but it doesn't seem to work...
Could anybody help me please ?
https://code.sololearn.com/cpyoytLae1BU/?ref=app

Answer 1

the while loop inside "add_front" isn't quite right, just make it:

while((*c)->next){ // iterate through list until we reach tail not NULL
c = &(*c)->next;
}

and as @andriy kan did mentioned you need to swap the function names.

Answer 2

🇮🇳Omkar🕉
May be you are compiling 🦄Uni🦄's code on C++ compiler?
Errors you are writing about are given by C++ compiler, but not C compiler.
The code is valid C code, but not valid C++ code.

Answer 3

Mohamed ELomari thank you it worked !
But I don't understand the thing with the functions name...

Answer 4

🇮🇳Omkar🕉 oh right I see thank you

Answer 5

In your code function names contradict what they do:
in add_back you are trying to insert an item in front of a list
and in add_front you are trying to append an item to the end of a list.

I changed the function names as they should be. If you need your function naming just swap the function names.

I fixed only add_front and add_back. The rest of the code should work.

void add_front(cell *c, int n){
cell p=malloc(sizeof(cell));
p->val=n;
p->next=*c;
*c = p;
}

void add_back(cell *c, int n){
cell p=malloc(sizeof(cell));
p->val=n;
p->next=NULL;

if(!*c){
*c = p;
}else{
cell ptr = *c;
while(ptr->next) ptr = ptr->next;
ptr->next = p;
}
}

Answer 6

🦄Uni🦄 ,
You are using opposite naming of what we do by convention.

Suppose this is linked list:
list = a -> b -> c
when we use push_back() it means we are adding new element to 'rear' of list.

list.add_back(d);
//a->b->c->d

but in your code add_back() adds an element before the passed node(cell)

add_back(&c,k);
// a->b->k->c

Same goes for add_front()
by convention add_front will mean adding element at 'front' position, i.e as first element.

but in your code add_front() adds element after passed node (cell).

You can use whatever name you want 👀 but most of the people like to see it how it is by convention.

Answer 7

🦄Uni🦄

Correction that wrote Mohamed ELomari :
while((*c)->next){ // iterate through list until we reach tail not NULL
c = &(*c)->next;
}

is not enough to fix your code!

If you look at my corrections you could see that I also appended an additional check on empty list.

Without that check your code get access violation again if you try to add_back an item to an empty_list:

for example, try this:
int main() {
cell c=NULL;
add_back(&c, 1); // function add_back raise access violation
//....

also, code

cell ptr = *c;
while(ptr->next) ptr = ptr->next;

is more effective than

while((*c)->next){
c = &(*c)->next;
}

because the second one do the additional dereference operation in the loop

Answer 8

Blake and Nada Nedal please do not post irrelevant answers on this thread.

Answer 9

Mohamed ELomari
Your new code fix access violation issue.

My point was that 🦄Uni🦄 marked code with
while((*c)->next){
as correct answer
but it is not correct as the code doesn't check *c on NULL

To use extra dereference or do not is a matter of personal preference for the programmer.

Using of dereference operation at each iteration of a loop has some overhead.
For x86 platform it is not a big deal. Moreover, extra dereference may be optimized out with -O3 flag (max optimization for performance).
But for small devices where performance is a matter and its compiler is not such a good optimizer I prefer iterate over a list without additional dereference operation (as in my code). But it is only my preference.

Answer 10

Erisa Murati please do not spam this thread with irrelevant answers.

Answer 11

Segmentation faults 😁.

There are many things going wrong. first thing is typedef .

clang 5.0.2 gives error for redefinition :
'struct cell *' vs 'cell'

next thing to consider is that malloc returns a void pointer so you need to typecast it before assignment.

like this :
type * p = (type *) malloc(sizeof(type));

There are many other things that I failed to fix 😁. Just listed a few so that you can work on fixing them. Hope it helps.

Answer 12

andriy kan ,
Oh yes. Thanks for correction.

I compiled code without saving it. By default it's compiled as C++.

In C it's valid 👍
Thanks again.

Answer 13

@andriy kan this can fix the access violation issue and it does not have the if else statement:

void add_back(cell *c, int n){
cell p=malloc(sizeof(cell));
p->val=n;
while(*c) {
c=&(*c)->next;
}
p->next = *c;
*c = p;
}

Answer 14

Java

Answer 15

#include#
Int main()