Array Deletion at End in DSA C++ - Execution Trace

Concept Flow - Array Deletion at End

Start with array and size

↓

Check if array is empty?

↓

Reduce size by 1

↓

Updated array size

↓

End

Start with the array and its size, check if it's empty. If not, reduce the size by one to delete the last element.

Execution Sample

DSA C++

int arr[5] = {10, 20, 30, 40, 50};
int size = 5;
// Delete last element
if (size > 0) {
  size--;
}

This code deletes the last element of the array by reducing the size variable.

Execution Table

Step	Operation	Array Size	Notes	Visual State
1	Start with array and size=5	5	None	[10, 20, 30, 40, 50] size=5
2	Check if size > 0	5	None	[10, 20, 30, 40, 50] size=5
3	Reduce size by 1	4	None	[10, 20, 30, 40] size=4
4	End	4	None	[10, 20, 30, 40] size=4

💡 Size reduced from 5 to 4, last element logically deleted

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
size	5	5	4	4
arr	[10,20,30,40,50]	[10,20,30,40,50]	[10,20,30,40,50]	[10,20,30,40,50]

Key Moments - 2 Insights

Why does the array still show all elements after deletion?

Because the physical array elements remain unchanged; only the size variable is reduced to ignore the last element, as shown in execution_table step 3.

What happens if we try to delete when size is zero?

The deletion does not happen because the condition size > 0 fails, stopping the process as shown in concept_flow and execution_table step 2.

Visual Quiz - 3 Questions

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

A 4

B 5

C 3

D 0

💡 Hint

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

At which step does the size variable change?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at variable_tracker for 'size' changes and execution_table operations.

If size was 0 at start, what would happen?

A Size reduces to -1

B Deletion stops, size remains 0

C Array elements are removed physically

D Program crashes

💡 Hint

Refer to concept_flow decision for empty array and execution_table step 2.

Concept Snapshot

Array Deletion at End:
- Keep track of array size
- Check if size > 0 before deleting
- Deletion means reducing size by 1
- Physical array unchanged, size controls valid elements
- Prevent deletion if array empty

Full Transcript

This concept shows how to delete the last element of an array by reducing the size variable. The array itself remains unchanged physically, but the size variable controls how many elements are considered valid. The process starts by checking if the array is empty (size > 0). If not empty, the size is reduced by one, effectively deleting the last element. If empty, deletion stops. This method avoids shifting elements and is efficient for deletion at the end.

Practice

1. What happens to the size of an array when you delete an element from the end in a dynamic array?

easy

A. The size decreases by one

B. The size remains the same

C. The size increases by one

D. The size becomes zero

Solution

1. Step 1: Understand dynamic array size behavior

   When an element is deleted from the end, the array size reduces by one because one element is removed.

2. Step 2: Confirm size change after deletion

   Deleting from the end does not affect other elements, only reduces size by one.

3. Final Answer:

   The size decreases by one -> Option A

4. Quick Check:

   Size after deletion = original size - 1 [OK]

Hint: Deleting at end reduces size by one [OK]

Common Mistakes:

• Thinking size remains same after deletion
• Assuming size increases after deletion
• Confusing deletion at end with deletion at start

2. Which of the following is the correct syntax to delete the last element from a vector named vec in C++?

easy

A. vec.erase_end();

B. vec.delete_last();

C. vec.remove_end();

D. vec.pop_back();

Solution

1. Step 1: Recall vector deletion syntax

   The standard method to remove the last element from a vector in C++ is pop_back().

2. Step 2: Verify other options

   Other methods like delete_last(), remove_end(), and erase_end() do not exist in C++ STL vector.

3. Final Answer:

   vec.pop_back(); -> Option D

4. Quick Check:

   Use pop_back() to delete last element [OK]

Hint: Use pop_back() to remove last element in vector [OK]

Common Mistakes:

• Using non-existent methods like delete_last()
• Confusing erase() with erase_end()
• Trying to use remove_end() which is invalid

3. What will be the output of the following C++ code?

std::vector<int> v = {10, 20, 30, 40};
v.pop_back();
for(int x : v) std::cout << x << " ";

medium

A. 10 20 30 40

B. 20 30 40

C. 10 20 30

D. 10 20 40

Solution

1. Step 1: Understand pop_back effect on vector

   pop_back() removes the last element, which is 40 in this vector.

2. Step 2: Print remaining elements

   After removal, vector contains 10, 20, 30. Loop prints these with spaces.

3. Final Answer:

   10 20 30 -> Option C

4. Quick Check:

   Last element removed, output = 10 20 30 [OK]

Hint: pop_back() removes last element before printing [OK]

Common Mistakes:

• Printing original vector without deletion
• Confusing which element is removed
• Forgetting pop_back() modifies vector

4. Identify the error in the following code that attempts to delete the last element of an array:

int arr[3] = {1, 2, 3};
arr.pop_back();

medium

A. pop_back() deletes first element, not last

B. pop_back() is not a member of built-in arrays

C. Array size is zero, cannot delete

D. No error, code is correct

Solution

1. Step 1: Check array type and methods

   Built-in arrays in C++ do not have member functions like pop_back().

2. Step 2: Understand correct usage

   pop_back() is a method of std::vector, not raw arrays.

3. Final Answer:

   pop_back() is not a member of built-in arrays -> Option B

4. Quick Check:

   pop_back() only works with vectors, not arrays [OK]

Hint: pop_back() works only on vectors, not raw arrays [OK]

Common Mistakes:

• Assuming pop_back() works on raw arrays
• Ignoring that arrays have fixed size
• Thinking pop_back() deletes first element

5. You have a vector v with elements {5, 10, 15, 20, 25}. You want to delete the last two elements and then print the vector. Which code snippet correctly does this?

hard

A. v.erase(v.end()-2, v.end()); for(auto x : v) std::cout << x << ' ';

B. v.pop_back(); for(auto x : v) std::cout << x << ' ';

C. v.remove_end(); v.remove_end(); for(auto x : v) std::cout << x << ' ';

D. v.pop_back(2); for(auto x : v) std::cout << x << ' ';

Solution

1. Step 1: Understand methods to delete multiple elements

   pop_back() removes only one element at a time. To remove two, it must be called twice. erase() can remove a range efficiently.

2. Step 2: Analyze the snippets

   The snippet v.erase(v.end()-2, v.end()); for(auto x : v) std::cout << x << ' '; correctly removes the last two elements. The snippet with a single v.pop_back(); removes only one element. remove_end() does not exist. pop_back(2) uses invalid syntax.

3. Final Answer:

   v.erase(v.end()-2, v.end()); for(auto x : v) std::cout << x << ' '; -> Option A

4. Quick Check:

   erase() with range removes last two elements efficiently [OK]

Hint: Use erase(end()-2, end()) to delete last two elements [OK]

Common Mistakes:

• Using pop_back() only once instead of twice
• Using non-existent remove_end() method
• Not knowing erase() can remove ranges