Pointer declaration - 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.

beginner

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

Use the syntax: int *ptr; where 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 to the type specified before it.

intermediate

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

Both declare a pointer to an int. The placement of * does not change the meaning; it's a style choice.

intermediate

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

The pointer contains a garbage address and 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 *float ptr;

D ptr float*;

The correct syntax is float *ptr; where the asterisk indicates a pointer.

What does the pointer variable store?

A The value of another variable

B The memory address of another variable

C The size of a variable

D The type of a variable

Pointers store the memory address where another variable is located.

How do you declare a pointer to a character?

A ptr char*;

B char ptr*;

C *char ptr;

D char* ptr;

The correct declaration is char* ptr;.

What is wrong with this declaration? int ptr;

A It declares an integer variable, not a pointer

B It declares a pointer to a pointer

C It declares a pointer correctly

D It declares a pointer to a float

Without the asterisk, int ptr; declares a normal integer variable, not a pointer.

Which symbol is used to declare a pointer variable?

A #

B &

C *

D $

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

Describe how to declare a pointer to an integer and explain what it stores.

Think about how you tell the computer to hold an address instead of a value.

Explain why it is important to initialize a pointer before using it.

Imagine using a map with a wrong address.

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