Dynamic Stack Using Resizable Array in DSA C - Execution Trace

Concept Flow - Dynamic Stack Using Resizable Array

Start

↓

Push Operation

↓

Check if array is full?

No→Add element at top

Yes↓

Double array size

↓

Copy old elements to new array

↓

Add element at top

↓

Update top pointer

↓

Done

↓

Pop Operation

↓

Check if stack empty?

Yes→Error: Underflow

No↓

Remove element at top

↓

Update top pointer

↓

Check if array too empty?

Yes↓

Halve array size

↓

Copy elements to smaller array

↓

Done

This flow shows how the stack uses an array that grows or shrinks dynamically when pushing or popping elements.

Execution Sample

DSA C

push(10)
push(20)
push(30)
pop()
push(40)

This code pushes three elements, pops one, then pushes another, showing dynamic resizing.

Execution Table

Step	Operation	Array Size	Top Index	Pointer Changes	Visual State
1	push(10)	2	0	top=0	[10, _] (top at index 0)
2	push(20)	2	1	top=1	[10, 20] (top at index 1)
3	push(30) triggers resize	4	2	resize array to 4, top=2	[10, 20, 30, _] (top at index 2)
4	pop()	4	1	top=1	[10, 20, _, _] (top at index 1)
5	push(40)	4	2	top=2	[10, 20, 40, _] (top at index 2)

💡 Execution stops after the last push; array resized once when full.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5
array_size	2	2	2	4	4	4
top_index	-1	0	1	2	1	2
stack_elements	[]	[10]	[10,20]	[10,20,30]	[10,20]	[10,20,40]

Key Moments - 3 Insights

Why does the array size double when pushing the third element?

At step 3 in execution_table, the array is full (size 2, top at 1). To add a new element, the array doubles to size 4 to have space.

Why does the top index decrease after pop at step 4?

Pop removes the top element, so top index moves down from 2 to 1, reflecting the new top element at index 1.

Why is the array size not reduced after popping one element?

The array size shrinks only when the number of elements is much smaller than the array size to save space, which does not happen at step 4.

Visual Quiz - 3 Questions

Look at the execution_table, what is the array size after step 3?

A 2

B 4

C 3

D 5

💡 Hint

Check the 'Array Size' column at step 3 in execution_table.

At which step does the top index move from 1 to 2?

A Step 3

B Step 4

C Step 2

D Step 5

💡 Hint

Look at 'Top Index' changes in execution_table between steps 2 and 3.

If we pop twice after step 5, what will happen to the array size?

A It will stay the same

B It will double

C It will halve

D It will reset to zero

💡 Hint

Recall that array size halves when stack is much emptier, as explained in key_moments.

Concept Snapshot

Dynamic Stack Using Resizable Array:
- Uses array to store stack elements
- Push adds element; if full, array size doubles
- Pop removes element; if too empty, array size halves
- Top index tracks current top
- Efficient memory use by resizing dynamically

Full Transcript

This visualization shows how a dynamic stack works using a resizable array. When pushing elements, if the array is full, it doubles in size to fit more elements. When popping elements, if the stack becomes too empty, the array halves its size to save space. The top index points to the current top element. The execution table traces each push and pop, showing array size, top index, and the stack's visual state. Key moments clarify why resizing happens and how the top index changes. The quiz tests understanding of array size changes and top index movements.