Array Deletion at End in DSA C++ - Build from Scratch

Array Deletion at End

📖 Scenario: You are managing a list of tasks to do today. Sometimes, you finish the last task and want to remove it from your list.

🎯 Goal: Build a simple program that stores a list of tasks in an array and removes the last task when done.

📋 What You'll Learn

Create an array called tasks with exactly 5 task names as strings

Create an integer variable called size to store the current number of tasks

Write code to remove the last task by decreasing size by 1

Print the tasks remaining in the array after deletion using a for loop

💡 Why This Matters

🌍 Real World

Managing lists like tasks, shopping items, or appointments often requires adding or removing items from the end.

💼 Career

Understanding how to manipulate arrays and track their size is fundamental for software development and data handling.

1

Create the tasks array

Create a string array called tasks with these exact values: "Laundry", "Dishes", "Homework", "Groceries", "Call Mom".

DSA C++

// Your code here

Hint

Use std::string tasks[5] = { ... }; to create the array with exact task names.

2

Set the size variable

Create an integer variable called size and set it to 5 to represent the number of tasks in the array.

DSA C++

std::string tasks[5] = {"Laundry", "Dishes", "Homework", "Groceries", "Call Mom"};
// Your code here

Hint

Use int size = 5; to store the number of tasks.

3

Remove the last task

Decrease the value of size by 1 to remove the last task from the list.

DSA C++

std::string tasks[5] = {"Laundry", "Dishes", "Homework", "Groceries", "Call Mom"};
int size = 5;
// Your code here

Hint

Use size = size - 1; to reduce the number of tasks by one.

4

Print remaining tasks

Use a for loop with int i = 0 to i < size to print each task in tasks on its own line.

DSA C++

std::string tasks[5] = {"Laundry", "Dishes", "Homework", "Groceries", "Call Mom"};
int size = 5;
size = size - 1;
// Your code here

Hint

Use for (int i = 0; i < size; i++) and std::cout << tasks[i] << std::endl; to print tasks.

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