1 00:00:00,450 --> 00:00:07,140 ‫So now we're going to create our push member function for our STACK class and PUSH is going to look 2 00:00:07,140 --> 00:00:09,090 ‫like this. 3 00:00:09,360 --> 00:00:16,650 ‫And because we're using a linked list to implement our stack, we can borrow from the pre append function. 4 00:00:17,070 --> 00:00:21,110 ‫So we'll start push off like this, we'll pass it a value. 5 00:00:21,120 --> 00:00:26,790 ‫We'll use that value to create a new node like this. 6 00:00:27,120 --> 00:00:32,850 ‫And if you wrote this function, borrowing from the pre pin function, you probably started this out 7 00:00:32,850 --> 00:00:33,990 ‫with an if statement. 8 00:00:33,990 --> 00:00:39,090 ‫If the height is equal to zero, that is this situation. 9 00:00:39,980 --> 00:00:48,110 ‫We'll set top to be equal to new node like this and then we'll write our code for when we do have items 10 00:00:48,110 --> 00:00:53,750 ‫in the stack, we'll say else and we'll build out this else statement. 11 00:00:54,670 --> 00:01:01,480 ‫We'll set new node next to be equal to top new node next is that yellow arrow there. 12 00:01:01,480 --> 00:01:06,790 ‫When we set it to top, we're having it point to the same node that top is pointing to. 13 00:01:07,710 --> 00:01:14,640 ‫And the wolves say top is equal to new node that moves that up and adds that node into the stack. 14 00:01:15,560 --> 00:01:18,590 ‫So let's add this in with the rest of our code. 15 00:01:19,040 --> 00:01:24,740 ‫So this is probably what your code looks like if you borrowed from the pre penned function. 16 00:01:25,130 --> 00:01:31,430 ‫But because we don't have a tail or the equivalent of tail, we would call that bottom here. 17 00:01:31,670 --> 00:01:39,320 ‫We don't need to have a separate if statement for when the stack is empty and then an alt statement 18 00:01:39,320 --> 00:01:41,900 ‫for when the stack has items. 19 00:01:42,320 --> 00:01:49,160 ‫We only needed to do this in the pre pin function because the linked list had a tail. 20 00:01:49,550 --> 00:01:57,650 ‫So we can use just these two lines that are in the ELT statement and remove the if and else. 21 00:01:58,310 --> 00:02:04,970 ‫So I'm going to move this up and show that this actually works for an empty stack. 22 00:02:05,810 --> 00:02:10,010 ‫First we have new node, next equals top. 23 00:02:10,460 --> 00:02:18,560 ‫So you can see here that new node next equals null pointer and top equals null pointer. 24 00:02:18,980 --> 00:02:21,560 ‫So that actually doesn't change anything. 25 00:02:21,560 --> 00:02:30,020 ‫Then we move to the next line, top equals new node, and that adds that new node onto our stack. 26 00:02:30,690 --> 00:02:36,090 ‫Now the only thing left to do is to increase the height by one. 27 00:02:36,600 --> 00:02:42,870 ‫So I do want to say that if you wrote it the other way with the if and the else, it is still going 28 00:02:42,870 --> 00:02:44,550 ‫to work just fine. 29 00:02:44,970 --> 00:02:48,420 ‫But doing it this way is a little bit more concise. 30 00:02:48,870 --> 00:02:56,430 ‫So we'll look at this code in a moment in vs code, and when we do, we'll create a new stack with one 31 00:02:56,430 --> 00:03:02,880 ‫node with a value of two, and then we'll run our push function and push on a node with a value of one 32 00:03:02,880 --> 00:03:06,810 ‫and that will print out that stack and we should see one, two. 33 00:03:07,200 --> 00:03:10,140 ‫So let's flip over and take a look at this. 34 00:03:10,850 --> 00:03:18,950 ‫So there is our push member function added to our stack class and I'm going to scroll up a bit here. 35 00:03:19,160 --> 00:03:25,550 ‫And this line here creates that stack with a node with a value of two, and then we're going to run, 36 00:03:25,550 --> 00:03:29,660 ‫push and add that second node with a value of one. 37 00:03:29,660 --> 00:03:37,160 ‫And then with this line we'll print that out and I'll run this and you can see that our stack has one 38 00:03:37,160 --> 00:03:42,830 ‫and two, and that is our function for push.