Pointer declaration in C++ - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this pointer declaration code?

Consider the following C++ code snippet. What will be printed when it runs?

C++

#include <iostream>
int main() {
    int x = 10;
    int* p = &x;
    std::cout << *p << std::endl;
    return 0;
}

A Address of x

B 0

C Compilation error

D 10

💡 Hint

Remember that *p means the value pointed to by p.

The pointer p holds the address of x. Using *p accesses the value stored at that address, which is 10.

❓ Predict Output

intermediate

What is the value of variable 'p' after this declaration?

Look at this code snippet. What does the pointer 'p' hold immediately after declaration?

C++

int* p;

A It holds the address of some variable

B It holds nullptr

C It holds a garbage (undefined) value

D It holds 0

💡 Hint

Uninitialized pointers do not automatically point to nullptr.

Declaring a pointer without initializing it means it contains whatever random data was in memory at that location, called a garbage value.

❓ Predict Output

advanced

What error does this pointer declaration cause?

What error will this code produce?

C++

int* p = 5;

A Compilation error: cannot convert int to int*

B Runtime error: segmentation fault

C Warning but compiles

D No error, p points to address 5

💡 Hint

You cannot assign an integer directly to a pointer without casting.

Assigning an integer literal to a pointer without a cast is invalid in C++ and causes a compilation error.

❓ Predict Output

advanced

What is the output of this pointer declaration and dereference?

What will this program print?

C++

#include <iostream>
int main() {
    int x = 7;
    int* p = &x;
    *p = 20;
    std::cout << x << std::endl;
    return 0;
}

A 20

B Garbage value

C Compilation error

D 7

💡 Hint

Changing *p changes the value of x because p points to x.

The pointer p points to x. Changing *p changes x's value to 20, so printing x outputs 20.

🧠 Conceptual

expert

Which pointer declaration is correct for a pointer to a constant integer?

You want to declare a pointer that points to an integer value that cannot be changed through the pointer. Which declaration is correct?

A int* const p;

B const int* p;

C const int* const p;

D int const p*;

💡 Hint

The const keyword before int means the value pointed to is constant.

const int* p means p points to a constant int value (value cannot be changed via p). int* const p means p itself is constant (cannot point elsewhere), but value can change. const int* const p means both pointer and value are constant. int const p* is invalid syntax.

Practice

1. Which of the following correctly declares a pointer to an integer in C++?

easy

A. ptr int*;

B. int ptr*;

C. *int ptr;

D. int *ptr;

Solution

1. Step 1: Understand pointer declaration syntax

   In C++, a pointer to a type is declared by writing the type followed by an asterisk (*) and then the pointer name.

2. Step 2: Check each option

   int *ptr; uses int *ptr; which is the correct syntax. Other options place the asterisk incorrectly.

3. Final Answer:

   int *ptr; -> Option D

4. Quick Check:

   Pointer declaration = type *name [OK]

Hint: Remember: type *name; declares a pointer [OK]

Common Mistakes:

• Placing * after the variable name
• Using * before the type keyword
• Omitting the * entirely

2. Which of the following is the correct syntax to declare a pointer to a double variable named p?

easy

A. double *p;

B. p double*;

C. *double p;

D. double p*;

Solution

1. Step 1: Recall pointer declaration rules

   The pointer declaration syntax is type *pointerName;. The asterisk (*) must come immediately before the pointer name.

2. Step 2: Evaluate options

   double *p; correctly declares double *p;. Other options have misplaced asterisks or wrong order.

3. Final Answer:

   double *p; -> Option A

4. Quick Check:

   Pointer to double = double *p; [OK]

Hint: Put * right before pointer name, after type [OK]

Common Mistakes:

• Writing * after the variable name
• Placing * before the type keyword
• Swapping variable and type order

3. What is the output of the following code?

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

medium

A. Garbage value

B. Address of x

C. 10

D. Compilation error

Solution

1. Step 1: Understand pointer initialization

   The pointer p is assigned the address of x using &x. So p points to x.

2. Step 2: Dereference pointer to get value

   The expression *p accesses the value stored at the address p points to, which is 10.

3. Final Answer:

   10 -> Option C

4. Quick Check:

   *p gives value at address = 10 [OK]

Hint: Dereference pointer *p to get variable value [OK]

Common Mistakes:

• Printing pointer variable instead of dereferenced value
• Confusing & (address) with * (dereference)
• Expecting address output instead of value

4. Identify the error in the following code snippet:

int a = 5;
int *ptr;
*ptr = a;

medium

A. Pointer ptr is not initialized before dereferencing

B. Variable a is not declared

C. Incorrect pointer declaration syntax

D. Missing semicolon after declaration

Solution

1. Step 1: Check pointer initialization

   The pointer ptr is declared but not assigned any address before dereferencing.

2. Step 2: Understand dereferencing uninitialized pointer

   Dereferencing *ptr without initialization leads to undefined behavior or runtime error.

3. Final Answer:

   Pointer ptr is not initialized before dereferencing -> Option A

4. Quick Check:

   Uninitialized pointer dereference = error [OK]

Hint: Always initialize pointer before using *ptr [OK]

Common Mistakes:

• Dereferencing pointer before assigning address
• Assuming declaration initializes pointer
• Ignoring runtime errors from uninitialized pointers

5. Given the code below, which pointer declaration correctly allows p to point to a constant integer value?

const int val = 100;
// Which declaration is correct?

hard

A. int *p = &val;

B. const int *p = &val;

C. int *const p = &val;

D. int *p const = &val;

Solution

1. Step 1: Understand pointer to const int

   To point to a constant integer, the pointer must be declared as pointing to a const int to prevent modification.

2. Step 2: Analyze options

   int *p = &val; cannot assign const int* to int* (discards qualifiers). const int *p = &val; correctly declares pointer to const int. int *const p = &val; declares const pointer to int (type mismatch). int *p const = &val; invalid syntax.

3. Final Answer:

   const int *p = &val; -> Option B

4. Quick Check:

   Pointer to const int = const int *p [OK]

Hint: Use const int *p to point to constant int [OK]

Common Mistakes:

• Using int *p to point to const int
• Confusing const pointer and pointer to const
• Misplacing const keyword