Pointer declaration in C++ - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a pointer in C++?

A pointer is a variable that stores the memory address of another variable. It 'points' to the location where data is stored.

beginner

How do you declare a pointer to an integer in C++?

You declare it using the syntax: int* ptr; Here, ptr is a pointer to an integer.

beginner

What does the asterisk (*) mean in a pointer declaration?

The asterisk (*) indicates that the variable is a pointer type, meaning it holds the address of a variable of the specified type.

beginner

Explain the difference between int* ptr; and int *ptr;.

Both are the same. The position of the asterisk (*) does not change the meaning. It just shows ptr is a pointer to an int.

intermediate

What happens if you declare a pointer but do not initialize it?

The pointer will contain a garbage (random) address. Using it without initialization can cause errors or crashes.

Which of the following declares a pointer to a float?

A float* ptr;

B float ptr*;

C ptr* float;

D float &ptr;

The correct syntax is float* ptr; which declares ptr as a pointer to a float.

What does the pointer variable store?

A The size of a variable

B The value of another variable

C The memory address of another variable

D The type of a variable

Pointers store the memory address of another variable, not the value itself.

How do you declare a pointer to an integer named p?

A int p*;

B int &p;

C int p;

D int* p;

The correct declaration is int* p; which means p is a pointer to an int.

What is the value of an uninitialized pointer?

A Random garbage address

B NULL

C The address of the pointer itself

D 0

An uninitialized pointer contains a random garbage address and should not be used before initialization.

Which symbol is used to declare a pointer?

A &

B *

C #

D $

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

Describe how to declare a pointer to a variable in C++ and explain what it stores.

Think about how you tell the computer to remember where something is stored.

What risks are there if you use a pointer without initializing it first?

Consider what happens if you try to use a random address.

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