Arrays vs Other Data Structures When to Choose Arrays in DSA C - Build Both Approaches

Arrays vs Other Data Structures: When to Choose Arrays

📖 Scenario: You are working on a simple inventory system for a small bookstore. You need to store the prices of books in a way that allows quick access by position because the store owner often asks for the price of a book by its shelf number.

🎯 Goal: Build a program that uses an array to store book prices, then calculates how many books are priced below a certain threshold. This will help the store owner quickly find affordable books.

📋 What You'll Learn

Create an array called book_prices with exactly these 5 prices: 120, 85, 150, 60, 90

Create an integer variable called price_limit and set it to 100

Use a for loop with variable i to count how many books have prices less than price_limit

Print the count of affordable books using printf

💡 Why This Matters

🌍 Real World

Arrays are used in many real-world applications where you need to store a fixed number of items and access them quickly by their position, like storing prices, scores, or sensor readings.

💼 Career

Understanding arrays is fundamental for programming jobs because they are the building blocks for more complex data structures and algorithms.

1

Create the array of book prices

Create an integer array called book_prices with these exact values: 120, 85, 150, 60, 90

DSA C

// Your code here

Hint

Use the syntax int array_name[size] = {values}; to create the array.

2

Set the price limit

Create an integer variable called price_limit and set it to 100

DSA C

int book_prices[5] = {120, 85, 150, 60, 90};
// Your code here

Hint

Use int price_limit = 100; to create the variable.

3

Count books priced below the limit

Create an integer variable called count and set it to 0. Then use a for loop with variable i from 0 to 4 to check each price in book_prices. Inside the loop, if book_prices[i] is less than price_limit, increase count by 1.

DSA C

int book_prices[5] = {120, 85, 150, 60, 90};
int price_limit = 100;
// Your code here

Hint

Initialize count to zero before the loop. Use for (int i = 0; i < 5; i++) to loop through the array.

4

Print the count of affordable books

Use printf to print the value of count with the message: "Number of affordable books: %d\n"

DSA C

int book_prices[5] = {120, 85, 150, 60, 90};
int price_limit = 100;
int count = 0;
for (int i = 0; i < 5; i++) {
    if (book_prices[i] < price_limit) {
        count++;
    }
}
// Your code here

Hint

Use printf("Number of affordable books: %d\n", count); to print the result.

Practice

1. Which of the following is the best reason to choose an array over other data structures like linked lists or trees?

easy

A. When you need fast access to elements by index

B. When you want to easily insert or delete elements anywhere

C. When you need a flexible size that changes often

D. When you want to store key-value pairs

Solution

1. Step 1: Understand array access

   Arrays store elements in contiguous memory, so accessing by index is very fast (constant time).

2. Step 2: Compare with other structures

   Linked lists and trees have slower access by index because they require traversal. Arrays are best for fast index access.

3. Final Answer:

   When you need fast access to elements by index -> Option A

4. Quick Check:

   Fast index access = B [OK]

Hint: Arrays give fast index access, unlike linked lists [OK]

Common Mistakes:

• Thinking arrays are best for frequent insertions/deletions
• Confusing arrays with key-value stores
• Assuming arrays resize automatically

2. Which of the following is the correct way to declare an integer array of size 5 in C?

easy

A. int arr = new int[5];

B. int arr[5];

C. int arr();

D. array<int> arr(5);

Solution

1. Step 1: Recall C array syntax

   In C, arrays are declared with the type, name, and size in square brackets, like int arr[5];.

2. Step 2: Check other options

   int arr(); uses parentheses which is a function declaration. int arr = new int[5]; is C++ style with new. array<int> arr(5); is not valid C syntax.

3. Final Answer:

   int arr[5]; -> Option B

4. Quick Check:

   C arrays use square brackets for size = C [OK]

Hint: C arrays use square brackets for size declaration [OK]

Common Mistakes:

• Using parentheses instead of square brackets
• Using C++ style new keyword in C
• Confusing array declaration with function declaration

3. What will be the output of the following C code?

int arr[3] = {10, 20, 30};
printf("%d", arr[1]);

medium

A. 10

B. Compilation error

C. 20

D. 30

Solution

1. Step 1: Understand array initialization

   The array arr has elements 10 at index 0, 20 at index 1, and 30 at index 2.

2. Step 2: Identify printed element

   The code prints arr[1], which is the second element, value 20.

3. Final Answer:

   20 -> Option C

4. Quick Check:

   arr[1] = 20 [OK]

Hint: Array indexing starts at 0, so arr[1] is second element [OK]

Common Mistakes:

• Confusing index 1 with first element
• Expecting compilation error due to syntax
• Mixing up array initialization order

4. Identify the error in the following C code snippet that uses an array:

int arr[3];
arr[3] = 100;
printf("%d", arr[3]);

medium

A. Array index out of bounds error

B. Syntax error in array declaration

C. Missing semicolon after declaration

D. No error, code runs fine

Solution

1. Step 1: Check array size and indexing

   The array arr has size 3, so valid indices are 0, 1, and 2.

2. Step 2: Analyze the assignment and print

   The code assigns and prints arr[3], which is outside the valid range, causing out of bounds access.

3. Final Answer:

   Array index out of bounds error -> Option A

4. Quick Check:

   Index 3 invalid for size 3 array = A [OK]

Hint: Array indices go from 0 to size-1 only [OK]

Common Mistakes:

• Assuming index 3 is valid for size 3 array
• Thinking syntax error due to semicolon
• Believing code runs without error

5. You need to store a fixed number of sensor readings that will not change in size and require fast access by position. Which data structure is the best choice and why?

hard

A. Binary tree, because it keeps data sorted automatically

B. Linked list, because it allows easy insertion and deletion

C. Hash table, because it stores key-value pairs efficiently

D. Array, because it provides fast indexed access and fixed size

Solution

1. Step 1: Analyze requirements

   The sensor readings count is fixed and will not change, and fast access by position is needed.

2. Step 2: Match data structure features

   Arrays have fixed size and allow fast access by index. Linked lists are slower for access. Hash tables and trees serve different purposes.

3. Final Answer:

   Array, because it provides fast indexed access and fixed size -> Option D

4. Quick Check:

   Fixed size + fast access = Array = A [OK]

Hint: Fixed size and fast access? Choose array [OK]

Common Mistakes:

• Choosing linked list for fixed size data
• Confusing hash table use case
• Thinking binary tree is best for fixed size arrays