new operator in C++ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to allocate memory for an integer using the new operator.

C++

int* ptr = [1] int;

Drag options to blanks, or click blank then click option'

Anew

Bmalloc

Calloc

Dcreate

Attempts:

3 left

💡 Hint

Common Mistakes

Using malloc instead of new in C++.

Forgetting to use the new operator before the type.

The new operator allocates memory for an integer and returns a pointer to it.

2fill in blank

medium

Complete the code to allocate an array of 5 doubles using the new operator.

C++

double* arr = [1] double[5];

Drag options to blanks, or click blank then click option'

Anew

Bmalloc

Ccreate

Dalloc

Attempts:

3 left

💡 Hint

Common Mistakes

Using malloc which is a C function, not recommended in C++.

Forgetting the brackets for array allocation.

The new operator allocates memory for an array of doubles.

3fill in blank

hard

Fix the error in the code to correctly allocate a single float using new.

C++

float* fptr = [1] float();

Drag options to blanks, or click blank then click option'

Amalloc

Balloc

Ccreate

Dnew

Attempts:

3 left

💡 Hint

Common Mistakes

Using malloc which returns void* and requires casting.

Using incorrect keywords like create or alloc.

The new operator correctly allocates and initializes a float.

4fill in blank

hard

Fill both blanks to allocate and initialize an array of 3 integers with zeros using new.

C++

int* arr = [1] int[2];

Drag options to blanks, or click blank then click option'

Anew

B[3]{}

C()

D{}

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses instead of brackets for arrays.

Forgetting to use new keyword.

The new operator with square brackets allocates an array of integers.

5fill in blank

hard

Fill all three blanks to allocate an array of 4 chars and initialize them to zero using new.

C++

char* buffer = [1] char[2] [3];

Drag options to blanks, or click blank then click option'

Anew

B[4]

C()

D{}

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses instead of braces for initialization.

Forgetting to use new or brackets.

The new operator with brackets allocates an array, and braces initialize all elements to zero.

Practice

1. What does the new operator do in C++?

easy

A. Allocates memory dynamically and returns a pointer to it

B. Deletes a variable from memory

C. Declares a normal variable on the stack

D. Copies data from one variable to another

Solution

1. Step 1: Understand the purpose of new

   The new operator is used to allocate memory on the heap during program execution.

2. Step 2: Identify what new returns

   It returns a pointer to the allocated memory so the program can use it.

3. Final Answer:

   Allocates memory dynamically and returns a pointer to it -> Option A

4. Quick Check:

   new = allocate memory [OK]

Hint: Remember: new creates memory and gives a pointer [OK]

Common Mistakes:

• Confusing new with delete
• Thinking new declares stack variables
• Assuming new copies data

2. Which of the following is the correct syntax to allocate an integer using new?

easy

A. int p = new int;

B. int p = new int();

C. int *p = new int[];

D. int *p = new int;

Solution

1. Step 1: Check pointer declaration

   Using new returns a pointer, so the variable must be a pointer type like int *.

2. Step 2: Verify syntax correctness

   int *p = new int; correctly allocates an int and assigns its address to p.

3. Final Answer:

   int *p = new int; -> Option D

4. Quick Check:

   Pointer = new type [OK]

Hint: new returns pointer, so use pointer variable [OK]

Common Mistakes:

• Declaring variable without pointer
• Using parentheses incorrectly
• Assigning new to non-pointer variable

3. What is the output of this code?

int *arr = new int[3]{10, 20, 30};
std::cout << arr[1] << std::endl;
delete[] arr;

medium

A. 20

B. 10

C. 30

D. Runtime error

Solution

1. Step 1: Understand array allocation with new

   The code creates an array of 3 integers with values 10, 20, 30.

2. Step 2: Access the second element

   Array indexing starts at 0, so arr[1] is the second element, which is 20.

3. Final Answer:

   20 -> Option A

4. Quick Check:

   arr[1] = 20 [OK]

Hint: Remember array index starts at 0 [OK]

Common Mistakes:

• Confusing index 1 with index 0
• Forgetting to use delete[] for arrays
• Expecting runtime error without cause

4. Identify the error in this code snippet:

int *p = new int;
*p = 5;
delete p;
delete p;

medium

A. Incorrect use of new operator

B. Missing initialization of pointer

C. Double deletion of the same pointer

D. No error, code is correct

Solution

1. Step 1: Analyze pointer allocation and deletion

   Pointer p is allocated memory and deleted once correctly.

2. Step 2: Check for repeated delete

   Deleting p a second time causes undefined behavior (double deletion error).

3. Final Answer:

   Double deletion of the same pointer -> Option C

4. Quick Check:

   delete twice = error [OK]

Hint: Delete pointer only once to avoid errors [OK]

Common Mistakes:

• Deleting pointer twice
• Not deleting allocated memory
• Confusing delete and delete[]

5. You want to create a dynamic 2D array of integers with 3 rows and 2 columns using new. Which code correctly allocates and deallocates this array?

hard

A. int *arr = new int[3*2];
// use arr
delete arr;

B. int **arr = new int*[3];
for(int i=0; i<3; i++) arr[i] = new int[2];
// use arr
for(int i=0; i<3; i++) delete[] arr[i];
delete[] arr;

C. int **arr = new int[3][2];
// use arr
delete[] arr;

D. int arr[3][2];
// use arr
// no delete needed

Solution

1. Step 1: Allocate 2D array dynamically

   int **arr = new int*[3]; for(int i=0; i<3; i++) arr[i] = new int[2]; // use arr for(int i=0; i<3; i++) delete[] arr[i]; delete[] arr; correctly creates an array of pointers for rows, then allocates each row as an array of ints.

2. Step 2: Properly deallocate memory

   Each row is deleted with delete[], then the array of pointers is deleted with delete[].

3. Final Answer:

   Uses an array of pointers, allocating each row separately -> Option B

4. Quick Check:

   Nested new and delete[] for 2D arrays [OK]

Hint: Use nested new and delete[] for 2D arrays [OK]

Common Mistakes:

• Using delete instead of delete[] for arrays
• Not deleting all allocated rows
• Trying to allocate 2D array with single new incorrectly