How to insert nodes into list by looping? - c

Question

How to Implement in right way to store values into linked list? In this example the last element will be "0" . Is there a possible to write the content of while loop that allows me don't create the last node which will be "0" after allocating in while loop?
void store(Stack *a, t_important *data)
{
int i;
Stack *tmp;
tmp = a;
i = 0;
while(i < data->length)
{
tmp->n = data->collection_of_ints[i];
tmp->next = malloc(sizeof(Stack));
tmp = tmp->next;
i++;
}
}
Input:
2->6->0->1->3->5->4
Output:
2->6->0->1->3->5->4->0
It is my main function in where i call the store function.
int main(int ac, char **av)
{
Actions action;
Stack *a;
Stack *b;
t_important *data;
if(ac < 2)
return (-1);
data = malloc(sizeof(*data));
stack_nums_counter(av, data);
collect(av, data);
__check__collection(data);
__collecting_ints(data);
action = init();
a = NULL;
b = NULL;
store(&a, data);
__sort_a__(&a, &b, data, action);
return (0);
}

Answer 1

I would make store take a Stack** instead:
void store(Stack **a, t_important *data) {
// find last `next`
while(*a) a = &(*a)->next;
// insert values
for(int i = 0; i < data->length; ++i)
{
*a = malloc(sizeof **a);
(*a)->n = data->collection_of_ints[i];
a = &(*a)->next;
}
*a = NULL; // terminate the linked list
}
and then call it like so
Stack *my_stack = NULL;
store(&my_stack, &some_t_important_instance);
If you instead want to insert the important data first in the linked list, you skip the first while loop to find the last next member:
void store(Stack **a, t_important *data) {
Stack *old_first = *a;
// insert values
for(int i = 0; i < data->length; ++i)
{
*a = malloc(sizeof **a);
(*a)->n = data->collection_of_ints[i];
a = &(*a)->next;
}
// link the last inserted node to the old first node
*a = old_first;
}

Answer 2

You always have uninitialized last node of the stack
tmp->next = malloc(sizeof(Stack));
tmp = tmp->next;
So when the stack is outputted then the program invokes undefined behavior.
Also it seems within the caller instead of declaring a pointer of the type Stack * you declared an object of the type Stack and are passing a pointer to it. It is a bad approach.
Nevertheless using your approach the function can be defined the following way
void store(Stack *a, t_important *data)
{
int i;
Stack *tmp;
tmp = a;
i = 0;
while(i < data->length)
{
if ( i != 0 )
{
tmp->next = malloc(sizeof(Stack));
tmp = tmp->next;
}
tmp->n = data->collection_of_ints[i];
tmp->next = NULL;
i++;
}
}