Pointer declaration

Introduction

Pointers let you store the address of a variable so you can work with the variable's location directly.

When you want to change a variable's value inside a function.

When you need to work with arrays or strings efficiently.

When you want to manage dynamic memory.

When you want to pass large data structures without copying them.

When you need to create complex data structures like linked lists.

Syntax

C

type *pointerName;

The asterisk (*) shows that the variable is a pointer.

The pointer stores the memory address of a variable of the specified type.

Examples

Declares a pointer p that can hold the address of an int variable.

C

int *p;

Declares a pointer cptr that can hold the address of a char variable.

C

char *cptr;

Declares a pointer fptr that can hold the address of a float variable.

C

float *fptr;

Sample Program

This program shows how to declare a pointer, assign it the address of a variable, and access the value through the pointer.

C

#include <stdio.h>

int main() {
    int num = 10;
    int *ptr = &num;  // ptr stores the address of num

    printf("Value of num: %d\n", num);
    printf("Address of num: %p\n", (void*)&num);
    printf("Value stored in ptr (address of num): %p\n", (void*)ptr);
    printf("Value pointed to by ptr: %d\n", *ptr);

    return 0;
}

Important Notes

Use the ampersand (&) to get the address of a variable.

Use the asterisk (*) to access the value stored at the pointer's address.

Always initialize pointers before using them to avoid errors.

Summary

Pointers store memory addresses of variables.

Use * to declare a pointer and to access the value it points to.

Use & to get the address of a variable.

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