Why pointers are needed in C++ - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a pointer to an integer.

C++

int x = 10;
int * [1] = &x;

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

Ap

B*p

C&p

Dp*

Attempts:

3 left

💡 Hint

Common Mistakes

Using '*' in the variable name instead of in the type declaration.

We declare a pointer variable by specifying its name, here p. The asterisk (*) is used when defining the pointer type, not in the variable name.

2fill in blank

medium

Complete the code to access the value pointed to by the pointer.

C++

int x = 20;
int *p = &x;
int y = [1]p;

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

A*

B->

C&

D%

Attempts:

3 left

💡 Hint

Common Mistakes

Using '&' instead of '*' to access the value.

The asterisk (*) operator is used to dereference a pointer, which means accessing the value stored at the address the pointer holds.

3fill in blank

hard

Fix the error in the code to correctly assign the pointer.

C++

int x = 30;
int *p;
p = [1]x;

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

Ap

Bx

C*x

D&x

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning the value instead of the address to the pointer.

To assign a pointer to the address of a variable, use the address-of operator '&'.

4fill in blank

hard

Fill both blanks to create a pointer to a pointer and access the original value.

C++

int x = 40;
int *p = &x;
int **pp = [1];
int y = [2]pp;

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

A&p

B*pp

C**pp

Dp

Attempts:

3 left

💡 Hint

Common Mistakes

Using single dereference when double is needed.

Assigning pointer value instead of its address.

To create a pointer to a pointer, assign the address of the first pointer using '&p'. To access the original value, dereference twice using '**pp'.

5fill in blank

hard

Fill all three blanks to create a dynamic array, assign values, and access an element.

C++

int *arr = new int[[1]];
arr[0] = [2];
int first = arr[[3]];

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

A5

B10

C0

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong index to access array element.

Assigning value to wrong index.

We create a dynamic array of size 5, assign 10 to the first element (index 0), and access that element.

Practice

1. Why do we need pointers in C++ programming?

easy

A. To directly access and modify memory locations

B. To write comments in the code

C. To create loops easily

D. To define new data types

Solution

1. Step 1: Understand what pointers represent

   Pointers store the address of a variable in memory, not the variable's value itself.

2. Step 2: Recognize the benefit of direct memory access

   This allows programs to directly access and modify data stored in memory, which is not possible with normal variables alone.

3. Final Answer:

   To directly access and modify memory locations -> Option A

4. Quick Check:

   Pointers = direct memory access [OK]

Hint: Pointers hold addresses to access data directly [OK]

Common Mistakes:

• Thinking pointers are used for comments
• Confusing pointers with loops
• Believing pointers define new data types

2. Which of the following is the correct way to declare a pointer to an integer in C++?

easy

A. int *ptr;

B. int ptr*;

C. *int ptr;

D. pointer int ptr;

Solution

1. Step 1: Recall pointer declaration syntax

   In C++, a pointer to a type is declared by placing an asterisk (*) before the pointer name after the type.

2. Step 2: Match the correct syntax

   Among the options, only 'int *ptr;' correctly declares a pointer to an integer.

3. Final Answer:

   int *ptr; -> Option A

4. Quick Check:

   Pointer declaration = type *name [OK]

Hint: Pointer syntax: type *pointerName; [OK]

Common Mistakes:

• Placing * after the pointer name
• Using invalid keywords like 'pointer'
• Misplacing the asterisk before the type

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

int x = 10;
int *p = &x;
*p = 20;
std::cout << x;

medium

A. Compilation error

B. 10

C. Address of x

D. 20

Solution

1. Step 1: Understand pointer assignment and dereferencing

   Pointer p stores the address of x. Using *p = 20; changes the value at that address, which is x.

2. Step 2: Determine the value of x after modification

   Since *p = 20 modifies x, printing x outputs 20.

3. Final Answer:

   20 -> Option D

4. Quick Check:

   *p changes x = 20 [OK]

Hint: Dereference pointer to change original variable [OK]

Common Mistakes:

• Thinking *p prints address instead of value
• Assuming x remains unchanged
• Confusing pointer declaration with value assignment

4. Identify the error in this code snippet:

int a = 5;
int *p;
*p = a;
std::cout << *p;

medium

A. Variable a is not declared

B. Pointer p is not initialized before dereferencing

C. Incorrect pointer syntax

D. Missing semicolon after declaration

Solution

1. Step 1: Check pointer initialization

   Pointer p is declared but not assigned any address before using *p = a;, which causes undefined behavior.

2. Step 2: Understand consequences of uninitialized pointer

   Dereferencing an uninitialized pointer leads to runtime errors or crashes.

3. Final Answer:

   Pointer p is not initialized before dereferencing -> Option B

4. Quick Check:

   Initialize pointer before use [OK]

Hint: Always assign pointer before dereferencing [OK]

Common Mistakes:

• Ignoring pointer initialization
• Assuming variable a is missing
• Thinking syntax is incorrect

5. You want a function to modify an integer variable defined in main(). Which is the best way to achieve this using pointers?

hard

A. Pass the variable's value to the function

B. Use a global variable instead

C. Pass the variable's pointer to the function and modify via dereferencing

D. Return a new value from the function and assign it in main()

Solution

1. Step 1: Understand function parameter passing

   Passing a variable's value copies it, so changes inside the function don't affect the original.

2. Step 2: Use pointers to modify original variable

   Passing the variable's pointer allows the function to access and change the original variable by dereferencing the pointer.

3. Final Answer:

   Pass the variable's pointer to the function and modify via dereferencing -> Option C

4. Quick Check:

   Pointer parameter modifies original variable [OK]

Hint: Pass pointer to function to change original variable [OK]

Common Mistakes:

• Passing value only modifies copy
• Using global variables unnecessarily
• Relying on return value instead of pointers