delete operator in C++ - Mini Project: Build & Apply

Using the delete operator in C++

📖 Scenario: Imagine you are managing memory manually in a small C++ program. You create a dynamic integer variable but need to free its memory properly to avoid waste.

🎯 Goal: You will create a dynamic integer pointer, assign a value, then use the delete operator to free the memory, and finally print a message confirming deletion.

📋 What You'll Learn

Create a dynamic integer pointer called ptr using new and assign it the value 10

Create a boolean variable called isDeleted and set it to false

Use the delete operator on ptr and set isDeleted to true

Print "Memory deleted: true" exactly

💡 Why This Matters

🌍 Real World

Manual memory management is important in systems programming, embedded devices, and performance-critical applications.

💼 Career

Understanding how to allocate and free memory safely is a key skill for C++ developers working on software that controls hardware or requires efficient resource use.

1

Create a dynamic integer pointer

Create a dynamic integer pointer called ptr using new and assign it the value 10.

C++

// Your code here

Hint

Use new int(10) to allocate memory and assign 10.

2

Create a boolean flag for deletion

Create a boolean variable called isDeleted and set it to false.

C++

int* ptr = new int(10);
// Your code here

Hint

Use bool isDeleted = false; to create the flag.

3

Delete the dynamic memory and update flag

Use the delete operator on ptr and then set isDeleted to true.

C++

int* ptr = new int(10);
bool isDeleted = false;
// Your code here

Hint

Use delete ptr; to free memory and then isDeleted = true;.

4

Print confirmation message

Print the message "Memory deleted: true" exactly using std::cout.

C++

int* ptr = new int(10);
bool isDeleted = false;
delete ptr;
isDeleted = true;
// Your code here

Hint

Use std::cout << "Memory deleted: true" << std::endl; to print.

Practice

1. What is the main purpose of the delete operator in C++?

easy

A. To allocate new memory

B. To free memory allocated with new

C. To copy objects

D. To declare variables

Solution

1. Step 1: Understand memory allocation

   The new operator allocates memory dynamically on the heap.

2. Step 2: Role of delete

   The delete operator frees that allocated memory to avoid leaks.

3. Final Answer:

   To free memory allocated with new -> Option B

4. Quick Check:

   delete frees memory [OK]

Hint: Remember: new allocates, delete frees memory [OK]

Common Mistakes:

• Confusing delete with new
• Using delete to copy objects
• Thinking delete declares variables

2. Which of the following is the correct syntax to delete a dynamically allocated array arr?

easy

A. delete arr;

B. delete array arr;

C. delete arr[];

D. delete[] arr;

Solution

1. Step 1: Identify array deletion syntax

   For arrays allocated with new[], use delete[] to free all elements properly.

2. Step 2: Match correct syntax

   delete[] arr; correctly deletes the entire array.

3. Final Answer:

   delete[] arr; -> Option D

4. Quick Check:

   Use delete[] for arrays [OK]

Hint: Use delete[] for arrays, delete for single objects [OK]

Common Mistakes:

• Using delete instead of delete[] for arrays
• Placing brackets after variable name incorrectly
• Writing delete array arr (invalid syntax)

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

int* p = new int(10);
std::cout << *p << std::endl;
delete p;
// std::cout << *p << std::endl; // Uncommenting this line causes what?

medium

A. 10 and then 10 again

B. Compilation error at delete

C. 10 and then undefined behavior

D. Runtime error at new

Solution

1. Step 1: Analyze output before delete

   The pointer p points to an int with value 10, so *p prints 10.

2. Step 2: Effect of delete and accessing pointer

   After delete p;, the memory is freed. Accessing *p after delete causes undefined behavior (may crash or print garbage).

3. Final Answer:

   10 and then undefined behavior -> Option C

4. Quick Check:

   Access after delete = undefined behavior [OK]

Hint: Don't use pointer after delete; it's unsafe [OK]

Common Mistakes:

• Assuming deleted pointer still holds valid data
• Expecting compilation error on delete
• Ignoring undefined behavior risks

4. Identify the error in this code snippet:

int* arr = new int[5];
delete arr;

medium

A. Should use delete[] instead of delete

B. Should use delete without brackets

C. No error, code is correct

D. Should not delete dynamically allocated arrays

Solution

1. Step 1: Check allocation type

   arr is allocated with new int[5], which creates an array.

2. Step 2: Correct deletion method

   Arrays must be deleted with delete[] arr; to properly free all elements.

3. Final Answer:

   Should use delete[] instead of delete -> Option A

4. Quick Check:

   Array delete needs delete[] [OK]

Hint: Match new[] with delete[] always [OK]

Common Mistakes:

• Using delete for arrays causes undefined behavior
• Thinking delete works for both single and arrays
• Ignoring memory leaks from wrong delete

5. Consider this code:

int** matrix = new int*[3];
for (int i = 0; i < 3; ++i) {
    matrix[i] = new int[4];
}
// Code to delete matrix properly?

Which is the correct way to delete all allocated memory?

hard

A. for (int i = 0; i < 3; ++i) delete[] matrix[i]; delete[] matrix;

B. for (int i = 0; i < 3; ++i) delete matrix[i]; delete[] matrix;

C. delete[] matrix; delete[] matrix[0];

D. delete matrix; delete matrix[0];

Solution

1. Step 1: Understand allocation

   Each matrix[i] is an array allocated with new int[4], so must be deleted with delete[].

2. Step 2: Delete outer array

   The matrix pointer itself is an array of pointers allocated with new int*[3], so delete with delete[] matrix;.

3. Final Answer:

   for (int i = 0; i < 3; ++i) delete[] matrix[i]; delete[] matrix; -> Option A

4. Quick Check:

   Match new[] with delete[] at all levels [OK]

Hint: Delete inner arrays with delete[], then outer with delete[] [OK]

Common Mistakes:

• Using delete instead of delete[] for inner arrays
• Deleting outer array with delete instead of delete[]
• Forgetting to delete inner arrays causing leaks