Linked Lists Help C++ - c++

Question

I am having trouble in C++ putting and displaying array into a linked list. I'm having lots of trouble with linked lists in general
Here is my code. It only displays the first number. (It should display 19 21 17 22 33)
#include <iostream>
using namespace std;
struct node {
int age;
node *next;
};
void display(node *t)
{
node *temp = t;
cout << temp->age << " ";
}
int main()
{
int Age[5] = { 19, 21, 17, 22, 33 };
node* List = new node;
List = NULL;
node* temp2 = List;
while (temp2 != NULL)
{
temp2 = temp2->next;
node* List = new node;
List = NULL;
node* temp2 = List;
}
for (int i = 0; i < 5; i++)
{
temp2 = new node;
temp2 -> age = Age[i];
temp2 -> next = NULL;
if (List == NULL)
List = temp2;
}
display(List);
system("PAUSE");
return 0;
}

Answer 1

Take the following code as an example. Note that you have to delete all created nodes at the end of program to avoid memory leaks.
#include <iostream>
#include <cstddef>
using namespace std;
struct node {
int age;
node* next;
};
void display(node* list) {
while (list != NULL) {
cout << list->age << ' ';
list = list->next;
}
}
node* create(int age) {
node* t = new node;
t->age = age;
t->next = NULL;
return t;
}
void add(node* list, node* t) {
while (list->next != NULL) {
list = list->next;
}
list->next = t;
}
void release(node* list) {
while (list != NULL) {
node* t = list;
list = list->next;
delete t;
}
}
int main() {
int arr[5] = { 19, 21, 17, 22, 33 };
node* list = create(arr[0]);
for (int i = 1; i < 5; i++) {
node* t = create(arr[i]);
add(list, t);
}
display(list);
release(list);
system("PAUSE");
return 0;
}

Answer 2

There's a lot going on here. I'd recommend you look through some tutorials to help solidify your understanding of pointers and linked lists.
To answer your question, let's step through what's happening:
In your main function, you dynamically allocate a node object and have List point to this object. Then, you set List to NULL. When you initialize the node pointer temp2 to List, temp2 also points to NULL.
Because temp2 = NULL, you skip over the following while loop.
In the first iteration of your for loop, you re-assign temp2 to a newly created object, then set the age for that node to the Age[0]. When we get to your if statement, List = NULL so we enter the conditional statement and set List to temp2 where temp2->age = Age[0].
For each additional iteration of your for loop, List no longer is equal to NULL so you never enter your if statement again. List still points to the node where age = Age[0].
When you get to your display function, assuming it was written to loop through a linked list, your List pointer is a list with one node where age = 19. Assuming your had a linked list with multiple valid nodes, your display() function doesn't iterate over them.