Stack • Core Implementation

Stack using Arrays

The most straightforward way to build a Stack is by wrapping a standard Array and using a single integer variable `top` to keep track of the highest index.

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The Top Pointer

We initialize `top = -1`. This conceptually means "the array is completely empty". It's an index pointer, not a physical memory address.

Pushing

To push, we first increment `top`, and then place the element at `array[top]`. We must check if `top == size - 1` to prevent buffer overflow.

Popping

To pop, we read `array[top]` and then decrement `top`. We don't even need to "delete" the data from the array—it will just get overwritten next time we push!

Array `arr` (Size 4)

◀Top: -1

Code Tracker

:::

1let top = -1;

2function push(x) {

3 if (top >= size - 1) return 'Overflow';

4 top++;

5 arr[top] = x;

6}

7function pop() {

8 if (top < 0) return 'Underflow';

9 let val = arr[top];

10 top--;

11 return val;

12}

Stack Arrays

Stack Arrays

Stack using Arrays

The Top Pointer

Pushing

Popping

Stack using Arrays

The Top Pointer

Pushing

Popping