Why collections over arrays in C Sharp (C#) - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a list of integers.

C Sharp (C#)

List<int> numbers = new List<int>[1];

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

A()

B[]

C{}

D<>

Attempts:

3 left

💡 Hint

Common Mistakes

Using square brackets [] instead of parentheses.

Using curly braces {} which are for collection initializers.

In C#, to create a new list, you use parentheses () after the constructor name.

2fill in blank

medium

Complete the code to add an element to the list.

C Sharp (C#)

numbers.[1](5);

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

AAppend

BAdd

CInsert

DPush

Attempts:

3 left

💡 Hint

Common Mistakes

Using Append which is not a method on List.

Using Push which is used in stacks.

The Add method is used to add an element to a List in C#.

3fill in blank

hard

Fix the error in the code to check if the list contains the number 10.

C Sharp (C#)

bool hasTen = numbers.[1](10);

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

AHas

BIncludes

CExists

DContains

Attempts:

3 left

💡 Hint

Common Mistakes

Using Has which is not a List method.

Using Includes which is from JavaScript.

The Contains method checks if a list has a specific element.

4fill in blank

hard

Fill both blanks to create a dictionary and add a key-value pair.

C Sharp (C#)

Dictionary<string, int> ages = new Dictionary<string, int>[1];
ages.[2]("Alice", 30);

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

A()

BAdd

CInsert

D{}

Attempts:

3 left

💡 Hint

Common Mistakes

Using curly braces {} to create the dictionary without initial values.

Using Insert which is not a Dictionary method.

Use parentheses () to create the dictionary and Add to add a key-value pair.

5fill in blank

hard

Fill all three blanks to create a list, add an element, and check its count.

C Sharp (C#)

List<string> fruits = new List<string>[1];
fruits.[2]("Apple");
int count = fruits.[3];

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

A()

BAdd

CCount

DLength

Attempts:

3 left

💡 Hint

Common Mistakes

Using Length which is for arrays, not lists.

Forgetting parentheses when creating the list.

Create the list with (), add with Add, and get the number of items with Count.

Practice

1. Why might you choose a collection like List<T> over an array in C#?

easy

A. Because collections can change size dynamically while arrays have fixed size.

B. Because arrays have more built-in methods than collections.

C. Because collections use less memory than arrays.

D. Because arrays can store different data types in the same array.

Solution

1. Step 1: Understand array size behavior

   Arrays in C# have a fixed size once created and cannot grow or shrink.

2. Step 2: Understand collection size behavior

   Collections like List<T> can dynamically add or remove items, changing their size.

3. Final Answer:

   Because collections can change size dynamically while arrays have fixed size. -> Option A

4. Quick Check:

   Collections grow/shrink; arrays fixed size [OK]

Hint: Remember: arrays fixed size, collections flexible size [OK]

Common Mistakes:

• Thinking arrays can resize automatically
• Believing collections use less memory always
• Confusing data type storage capabilities

2. Which of the following is the correct way to declare a collection that can grow in size in C#?

easy

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

B. List<int> numbers = new List<int>();

C. int numbers = new List<int>();

D. ArrayList numbers = new int[5];

Solution

1. Step 1: Check syntax for array declaration

   int[] numbers = new int[5]; declares a fixed-size array, not a collection.

2. Step 2: Check syntax for collection declaration

   List<int> numbers = new List<int>(); correctly declares a generic list collection that can grow.

3. Final Answer:

   List<int> numbers = new List<int>(); -> Option B

4. Quick Check:

   List<T> syntax is for growable collections [OK]

Hint: Use List<T> for growable collections, arrays need size upfront [OK]

Common Mistakes:

• Using array syntax when collection is needed
• Assigning wrong types to variables
• Confusing ArrayList with arrays

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

List<int> nums = new List<int>() {1, 2, 3};
nums.Add(4);
Console.WriteLine(nums.Count);

medium

A. Compilation error

B. 3

C. 0

D. 4

Solution

1. Step 1: Understand initial list size

   The list nums starts with 3 elements: 1, 2, 3.

2. Step 2: Analyze the Add method effect

   Calling nums.Add(4); adds one more element, increasing count to 4.

3. Final Answer:

   4 -> Option D

4. Quick Check:

   List.Count reflects added elements [OK]

Hint: Add increases collection size; Count shows current size [OK]

Common Mistakes:

• Assuming Count stays 3 after Add
• Confusing Count with capacity
• Expecting compilation error due to Add

4. Identify the error in this code snippet:

int[] arr = new int[3];
arr.Add(5);

medium

A. Array size must be declared as 5.

B. int[] cannot store integers.

C. Arrays do not have an Add method.

D. The array must be initialized with values.

Solution

1. Step 1: Check array methods

   Arrays in C# do not have an Add method; this method belongs to collections like List.

2. Step 2: Understand array limitations

   Arrays have fixed size and cannot add elements dynamically.

3. Final Answer:

   Arrays do not have an Add method. -> Option C

4. Quick Check:

   Arrays lack Add method [OK]

Hint: Arrays fixed size, no Add method; use List for adding [OK]

Common Mistakes:

• Trying to add elements to arrays
• Confusing array size with element count
• Assuming arrays have collection methods

5. You need to store a list of user names that can change during program execution. Which approach is best and why?

hard

A. Use a List<string> because it can grow and shrink as users are added or removed.

B. Use an array because it is faster and fixed size is enough.

C. Use a fixed-size array and recreate it every time the list changes.

D. Use a string variable to store all names separated by commas.

Solution

1. Step 1: Analyze data size flexibility needs

   User names list changes size, so fixed size arrays are inconvenient.

2. Step 2: Choose collection type for dynamic data

   List<string> allows adding/removing names easily without recreating the structure.

3. Final Answer:

   Use a List<string> because it can grow and shrink as users are added or removed. -> Option A

4. Quick Check:

   Dynamic data needs collections like List [OK]

Hint: Dynamic data? Use List<T> for easy resizing [OK]

Common Mistakes:

• Choosing fixed arrays for changing data
• Using strings to store multiple values unsafely
• Recreating arrays repeatedly instead of collections