Pointer declaration - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a pointer to an integer.

C

int [1] ptr;

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

A*

B&

C#

D%

Attempts:

3 left

💡 Hint

Common Mistakes

Using & instead of * to declare a pointer.

Forgetting the * symbol entirely.

The asterisk (*) is used to declare a pointer variable in C.

2fill in blank

medium

Complete the code to declare a pointer to a character.

C

char [1] ch_ptr;

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

A&

B$

C^

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using & instead of * for pointer declaration.

Using symbols like ^ or $ which are invalid here.

The asterisk (*) is used to declare a pointer variable, here pointing to a char.

3fill in blank

hard

Fix the error in the pointer declaration.

C

float [1] ptr;

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

A*

B#

C&

D@

Attempts:

3 left

💡 Hint

Common Mistakes

Placing & instead of *.

Using invalid symbols like # or @.

The asterisk (*) must be placed before the pointer variable name to declare a pointer.

4fill in blank

hard

Fill both blanks to declare a pointer to a double and initialize it to NULL.

C

double [1] ptr = [2];

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

A*

BNULL

C0

D&

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 instead of NULL for pointer initialization.

Using & instead of * for pointer declaration.

The asterisk (*) declares the pointer, and NULL initializes it to point to nothing.

5fill in blank

hard

Fill all three blanks to declare a pointer to a constant integer and initialize it to NULL.

C

const int [1] ptr = [2]; // pointer to constant int

[3] value = 10;

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

A*

BNULL

Cint

D&

Attempts:

3 left

💡 Hint

Common Mistakes

Using & instead of * for pointer declaration.

Using wrong variable type for value.

Initializing pointer with 0 instead of NULL.

The asterisk (*) declares the pointer, NULL initializes it, and int declares the variable type.

Practice

1. What does the following declaration mean in C?
int *ptr;

easy

A. ptr is a pointer to a character variable

B. ptr is a pointer to an integer variable

C. ptr is an integer variable

D. ptr is a function returning an integer

Solution

1. Step 1: Understand the * symbol in declaration

   The * before ptr means ptr is a pointer variable, not a normal integer.

2. Step 2: Check the type before *

   The type before * is int, so ptr points to an integer variable.

3. Final Answer:

   ptr is a pointer to an integer variable -> Option B

4. Quick Check:

   int *ptr means pointer to int [OK]

Hint: Look for * before variable name to identify pointer [OK]

Common Mistakes:

• Thinking * means multiplication here
• Confusing pointer with normal variable
• Ignoring the type before *

2. Which of the following is the correct way to declare a pointer to a float variable in C?

easy

A. ptr float*;

B. float ptr*;

C. *float ptr;

D. float *ptr;

Solution

1. Step 1: Recall pointer declaration syntax

   Pointer declaration syntax is: type *name; so the * goes between type and variable name.

2. Step 2: Check each option

   float *ptr; matches correct syntax: float *ptr; others have wrong order or missing parts.

3. Final Answer:

   float *ptr; -> Option D

4. Quick Check:

   Pointer syntax = type *name; [OK]

Hint: Always put * between type and variable name [OK]

Common Mistakes:

• Placing * after variable name
• Putting * before type
• Missing * entirely

3. What is the output of this C code?

int x = 10;
int *p = &x;
printf("%d", *p);

medium

A. 10

B. Compilation error

C. Garbage value

D. Address of x

Solution

1. Step 1: Understand pointer initialization

   p is assigned the address of x using &x, so p points to x.

2. Step 2: Dereference pointer to get value

   *p means value at address p, which is x's value 10.

3. Final Answer:

   10 -> Option A

4. Quick Check:

   *p gives value at pointer address [OK]

Hint: Use * to get value from pointer address [OK]

Common Mistakes:

• Printing pointer p instead of *p
• Confusing address and value
• Forgetting & to get address

4. Identify the error in this pointer declaration:

int *p;
p = 5;

medium

A. Error: assigning integer directly to pointer

B. Correct: p points to integer 5

C. Error: missing * in assignment

D. Error: pointer must be initialized with & operator

Solution

1. Step 1: Check pointer assignment rules

   A pointer must hold a memory address, not a direct integer value.

2. Step 2: Analyze given assignment

   Assigning 5 directly to pointer p is invalid; it should be an address like &variable.

3. Final Answer:

   Error: assigning integer directly to pointer -> Option A

4. Quick Check:

   Pointer = address, not direct value [OK]

Hint: Pointers store addresses, never assign raw values directly [OK]

Common Mistakes:

• Assigning integer instead of address
• Forgetting & operator for address
• Confusing pointer and normal variable

5. Given the code below, which pointer declaration correctly allows modifying the value of num through the pointer?

int num = 20;
// Which declaration is correct?

hard

A. int *ptr = num;

B. int ptr = #

C. int *ptr = #

D. int &ptr = num;

Solution

1. Step 1: Understand pointer declaration for modifying variable

   To modify num via pointer, pointer must hold address of num, declared as int *ptr.

2. Step 2: Check each option

   int *ptr = # correctly declares pointer to int and assigns address of num. Others are invalid syntax or wrong types.

3. Final Answer:

   int *ptr = # -> Option C

4. Quick Check:

   Pointer to int = &variable for modification [OK]

Hint: Use int *ptr = &var to modify var via pointer [OK]

Common Mistakes:

• Assigning value instead of address
• Using wrong type for pointer
• Confusing references with pointers