Why Arrays Exist and What Problem They Solve in DSA C# - See It Work

Why Arrays Exist and What Problem They Solve

📖 Scenario: Imagine you run a small bookstore. You want to keep track of the prices of exactly 5 popular books you sell every day. You need a simple way to store these prices so you can quickly find and update them.

🎯 Goal: You will create an array to store the prices of 5 books. Then, you will set a price limit and find which books cost less than or equal to that limit. Finally, you will print those prices.

📋 What You'll Learn

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

Create an integer variable called priceLimit and set it to 100

Use a for loop with variable i to check each price in bookPrices

Inside the loop, add prices less than or equal to priceLimit to a new list called affordableBooks

Print the affordableBooks list prices separated by spaces

💡 Why This Matters

🌍 Real World

Stores and manages lists of items like prices, scores, or measurements in many apps.

💼 Career

Understanding arrays is essential for programming jobs that handle collections of data efficiently.

1

Create the array of book prices

Create an array called bookPrices with these exact prices: 120, 85, 150, 60, 90

DSA C#

// Create the array bookPrices with the given prices
// Your code here

Hint

Use int[] bookPrices = { ... }; to create the array with the exact prices.

2

Set the price limit

Create an integer variable called priceLimit and set it to 100

DSA C#

int[] bookPrices = {120, 85, 150, 60, 90};
// Create priceLimit variable and set it to 100
// Your code here

Hint

Use int priceLimit = 100; to create the variable.

3

Find affordable books using a loop

Create a list of integers called affordableBooks. Use a for loop with variable i to check each price in bookPrices. Inside the loop, if the price is less than or equal to priceLimit, add it to affordableBooks

DSA C#

int[] bookPrices = {120, 85, 150, 60, 90};
int priceLimit = 100;
// Create affordableBooks list
// Use for loop with i to check prices
// Add prices <= priceLimit to affordableBooks
// Your code here

Hint

Remember to create affordableBooks as a list before the loop. Use for (int i = 0; i < bookPrices.Length; i++) to loop through the array.

4

Print the affordable book prices

Use Console.WriteLine to print all prices in affordableBooks separated by spaces

DSA C#

using System.Collections.Generic;

int[] bookPrices = {120, 85, 150, 60, 90};
int priceLimit = 100;
List affordableBooks = new List();
for (int i = 0; i < bookPrices.Length; i++)
{
    if (bookPrices[i] <= priceLimit)
    {
        affordableBooks.Add(bookPrices[i]);
    }
}
// Print affordableBooks prices separated by spaces
// Your code here

Hint

Use Console.WriteLine(string.Join(" ", affordableBooks)); to print the list separated by spaces.

Practice

1. Why do arrays exist in programming languages like C#?

easy

A. To store multiple values of the same type in a single, fixed-size structure

B. To store different types of data in one variable

C. To perform mathematical calculations faster

D. To replace all other data structures

Solution

1. Step 1: Understand the purpose of arrays

   Arrays are designed to hold multiple values of the same type together in one place.

2. Step 2: Recognize the fixed size nature

   Arrays have a fixed size, meaning the number of elements is set when created.

3. Final Answer:

   To store multiple values of the same type in a single, fixed-size structure -> Option A

4. Quick Check:

   Arrays = fixed-size same-type storage [OK]

Hint: Arrays hold same-type items in fixed size [OK]

Common Mistakes:

• Thinking arrays can store different data types
• Believing arrays can change size dynamically
• Confusing arrays with lists or other collections

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

easy

A. int numbers = new int[5];

B. int[] numbers = new int[5];

C. int[] numbers = int[5];

D. array int numbers = new int(5);

Solution

1. Step 1: Recall C# array declaration syntax

   In C#, arrays are declared with the type followed by square brackets and initialized with 'new' keyword and size in brackets.

2. Step 2: Match syntax with options

   int[] numbers = new int[5]; matches the correct syntax: int[] numbers = new int[5];

3. Final Answer:

   int[] numbers = new int[5]; -> Option B

4. Quick Check:

   C# array declaration = int[] name = new int[size]; [OK]

Hint: Use type[], new keyword, and size in brackets [OK]

Common Mistakes:

• Missing square brackets after type
• Using parentheses instead of brackets for size
• Declaring array without 'new' keyword

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

int[] arr = new int[3];
arr[0] = 10;
arr[1] = 20;
arr[2] = 30;
for(int i = 0; i < arr.Length; i++)
{
    Console.Write(arr[i] + " ");
}

medium

A. Error: Index out of range

B. 0 0 0

C. 10 20 30

D. 10 20 30 0

Solution

1. Step 1: Analyze array initialization and assignments

   The array of size 3 is created with default values 0, then elements at indexes 0,1,2 are assigned 10, 20, 30 respectively.

2. Step 2: Trace the for loop output

   The loop prints each element separated by space: 10 20 30

3. Final Answer:

   10 20 30 -> Option C

4. Quick Check:

   Print assigned values in order [OK]

Hint: Arrays print assigned values in order [OK]

Common Mistakes:

• Assuming default values print instead of assigned
• Off-by-one errors in loop causing index errors
• Confusing output format with commas or no spaces

4. Identify the error in this C# code snippet that tries to create an array and assign values:

int[] nums = new int[2];
nums[0] = 5;
nums[1] = 10;
nums[2] = 15;

medium

A. Array size is too small for index 2 assignment

B. Syntax error in array declaration

C. Cannot assign values after array creation

D. Missing semicolon after array initialization

Solution

1. Step 1: Check array size and index usage

   The array is created with size 2, so valid indexes are 0 and 1 only.

2. Step 2: Identify invalid index assignment

   Assigning to nums[2] is out of bounds and causes runtime error.

3. Final Answer:

   Array size is too small for index 2 assignment -> Option A

4. Quick Check:

   Array size limits valid indexes [OK]

Hint: Array indexes start at 0 and end at size-1 [OK]

Common Mistakes:

• Trying to assign outside array bounds
• Confusing array size with last index
• Ignoring runtime exceptions from invalid index

5. You want to store daily temperatures for a week and calculate the average. Which problem does using an array solve best in this scenario?

hard

A. It stores temperatures with different data types together

B. It automatically sorts temperatures as they are added

C. It dynamically resizes when more days are added

D. It allows storing all temperatures in one fixed-size structure for easy access

Solution

1. Step 1: Understand the problem requirements

   We need to store exactly 7 temperature values, one for each day, and access them easily.

2. Step 2: Identify array benefits

   Arrays provide fixed-size storage with fast access by index, perfect for known-size data like a week.

3. Final Answer:

   It allows storing all temperatures in one fixed-size structure for easy access -> Option D

4. Quick Check:

   Fixed-size storage for known data length [OK]

Hint: Use arrays for fixed-size, same-type data [OK]

Common Mistakes:

• Thinking arrays auto-sort data
• Expecting arrays to resize dynamically
• Mixing data types in one array