Pointers and arrays in C++ - Mini Project: Build & Apply

Pointers and Arrays

📖 Scenario: You are learning how to use pointers to access elements in an array. Imagine you have a list of temperatures recorded over a week, and you want to use pointers to read these values.

🎯 Goal: Build a simple C++ program that creates an array of temperatures, uses a pointer to access the array elements, and prints each temperature using the pointer.

📋 What You'll Learn

Create an integer array called temps with exactly 7 values: 23, 25, 22, 20, 24, 26, 21

Create a pointer called ptr that points to the first element of temps

Use a for loop with an integer variable i from 0 to 6 to access array elements via the pointer

Print each temperature value accessed through the pointer inside the loop

💡 Why This Matters

🌍 Real World

Pointers and arrays are used in many programs to efficiently access and manipulate lists of data, such as sensor readings or user inputs.

💼 Career

Understanding pointers and arrays is essential for programming in C++ and systems programming jobs, where memory management and performance are important.

1

Create the array of temperatures

Create an integer array called temps with these exact values: 23, 25, 22, 20, 24, 26, 21.

C++

// Your code here

Hint

Use the syntax int temps[7] = {values}; to create the array.

2

Create a pointer to the array

Create a pointer called ptr that points to the first element of the temps array.

C++

int temps[7] = {23, 25, 22, 20, 24, 26, 21};
// Your code here

Hint

Use int* ptr = temps; to point to the first element of the array.

3

Use a for loop to access array elements via the pointer

Use a for loop with an integer variable i from 0 to 6 to access each element of temps through the pointer ptr. Inside the loop, access the element using *(ptr + i).

C++

int temps[7] = {23, 25, 22, 20, 24, 26, 21};
int* ptr = temps;
// Your code here

Hint

Use for (int i = 0; i < 7; i++) and inside the loop use *(ptr + i) to get each temperature.

4

Print each temperature using the pointer

Inside the for loop, print each temperature accessed through the pointer using std::cout. Print each temperature on its own line.

C++

int temps[7] = {23, 25, 22, 20, 24, 26, 21};
int* ptr = temps;
for (int i = 0; i < 7; i++) {
    int temp = *(ptr + i);
    // Your code here
}

Hint

Use std::cout << temp << std::endl; inside the loop to print each temperature.

Practice

1. What does the name of an array represent in C++?

easy

A. A copy of the entire array

B. The total size of the array

C. The last element of the array

D. A pointer to the first element of the array

Solution

1. Step 1: Understand array name behavior

   In C++, the name of an array acts as a pointer to its first element, not the whole array or size.

2. Step 2: Confirm pointer usage

   This pointer can be used to access elements by pointer arithmetic or indexing.

3. Final Answer:

   A pointer to the first element of the array -> Option D

4. Quick Check:

   Array name = pointer to first element [OK]

Hint: Remember array name points to element zero [OK]

Common Mistakes:

• Thinking array name stores size
• Confusing array name with last element
• Assuming array name copies data

2. Which of the following is the correct way to declare a pointer to an integer array named arr?

easy

A. int *ptr = &arr;

B. int ptr = &arr;

C. int *ptr = arr;

D. int ptr = arr;

Solution

1. Step 1: Understand pointer declaration

   To declare a pointer to an integer, use int *ptr. The array name arr acts as a pointer to its first element.

2. Step 2: Assign pointer correctly

   Assigning ptr = arr; sets the pointer to the first element's address. Using &arr gives the address of the whole array, which has a different type.

3. Final Answer:

   int *ptr = arr; -> Option C

4. Quick Check:

   Pointer to first element = int *ptr = arr [OK]

Hint: Use int *ptr = arr; to point to array start [OK]

Common Mistakes:

• Using &arr instead of arr for pointer
• Declaring pointer as int instead of int*
• Assigning pointer without *

3. What is the output of the following code?

int arr[] = {10, 20, 30};
int *p = arr;
std::cout << *(p + 1) << std::endl;

medium

A. 20

B. 10

C. 30

D. Compilation error

Solution

1. Step 1: Understand pointer arithmetic

   Pointer p points to arr[0]. Adding 1 moves pointer to arr[1].

2. Step 2: Dereference pointer at new position

   Dereferencing *(p + 1) gives the value at arr[1], which is 20.

3. Final Answer:

   20 -> Option A

4. Quick Check:

   *(p + 1) = arr[1] = 20 [OK]

Hint: Pointer + 1 points to next array element [OK]

Common Mistakes:

• Confusing pointer arithmetic with addition of values
• Dereferencing pointer without offset
• Expecting compilation error

4. Identify the error in the following code snippet:

int arr[3] = {1, 2, 3};
int *p = &arr;
std::cout << *(p + 2) << std::endl;

medium

A. Pointer declaration is correct, no error

B. Incorrect pointer assignment: &arr should be arr

C. Dereferencing pointer is invalid syntax

D. Array size is too small for pointer arithmetic

Solution

1. Step 1: Analyze pointer assignment

   arr is an array name acting as pointer to first element. &arr is address of whole array, type int (*)[3], incompatible with int *.

2. Step 2: Correct pointer assignment

   Assigning int *p = arr; is correct to point to first element. Using &arr causes type mismatch and incorrect pointer arithmetic.

3. Final Answer:

   Incorrect pointer assignment: &arr should be arr -> Option B

4. Quick Check:

   Use arr, not &arr, for int* pointer [OK]

Hint: Use arr, not &arr, when assigning int* pointer [OK]

Common Mistakes:

• Using &arr instead of arr for int*
• Ignoring pointer type mismatch warnings
• Assuming &arr points to first element

5. Given the code below, what will be the output?

int arr[] = {5, 10, 15, 20};
int *p = arr + 1;
std::cout << p[2] << std::endl;

hard

A. 20

B. 15

C. Undefined behavior

D. 10

Solution

1. Step 1: Understand pointer initialization

   p = arr + 1; points to arr[1], which is 10.

2. Step 2: Access element using pointer indexing

   p[2] means *(p + 2), which points to arr[3] (1 + 2 = 3), value 20.

3. Final Answer:

   20 -> Option A

4. Quick Check:

   p[2] = arr[3] = 20 [OK]

Hint: Pointer[index] = *(pointer + index) [OK]

Common Mistakes:

• Confusing p[2] with arr[2]
• Forgetting pointer offset starts at arr + 1
• Assuming p[2] is out of bounds