Why Arrays Exist and What Problem They Solve in DSA C# - Test Your Knowledge

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an array of integers with size 5.

DSA C#

int[] numbers = new int[[1]];

Drag options to blanks, or click blank then click option'

A0

B5

C10

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 as size creates an empty array.

Using 1 or 10 creates wrong size arrays.

The array size must be 5 to hold five integers.

2fill in blank

medium

Complete the code to access the first element of the array.

DSA C#

int first = numbers[[1]];

Drag options to blanks, or click blank then click option'

A0

B1

C5

D-1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1 as index causes skipping the first element.

Using negative or out-of-range indices causes errors.

Array indexing starts at 0, so the first element is at index 0.

3fill in blank

hard

Fix the error in the code to assign value 10 to the third element.

DSA C#

numbers[[1]] = 10;

Drag options to blanks, or click blank then click option'

A1

B3

C2

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using index 3 causes an out-of-range error.

Using index 1 assigns to the second element.

The third element is at index 2 because indexing starts at 0.

4fill in blank

hard

Fill both blanks to create an array and assign value 7 to its last element.

DSA C#

int[] arr = new int[[1]];
arr[[2]] = 7;

Drag options to blanks, or click blank then click option'

A4

B3

C5

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using index equal to size causes error.

Assigning to index 0 assigns first element, not last.

The array size is 5 (C), so the last element is at index 4 (A).

5fill in blank

hard

Fill all three blanks to create an array, assign 3 to first element, and 9 to last element.

DSA C#

int[] data = new int[[1]];
data[[2]] = 3;
data[[3]] = 9;

Drag options to blanks, or click blank then click option'

A0

B4

C5

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using index 5 causes out-of-range error.

Assigning first element at index 1 is incorrect.

The array size is 5, so indices go from 0 to 4. Assign 3 to index 0 (first element) and 9 to index 4 (last element).

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