Collection initialization syntax in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this C# collection initialization?

Consider the following C# code snippet that initializes a list of integers. What will be the content of the list after initialization?

C Sharp (C#)

var numbers = new List<int> { 1, 2, 3, 4, 5 };

A [1, 2, 3, 4, 5]

B [5, 4, 3, 2, 1]

C []

D [0, 1, 2, 3, 4]

💡 Hint

Look at the values inside the curly braces after the list declaration.

The list is initialized with the values 1 through 5 in order, so the list contains [1, 2, 3, 4, 5].

📝 Syntax

intermediate

Which option correctly initializes a dictionary with string keys and int values?

You want to create a dictionary in C# with keys "apple", "banana", and "cherry" and values 1, 2, and 3 respectively. Which of the following collection initializations is correct?

A var dict = new Dictionary<string, int> { ["apple"] = 1, ["banana"] = 2, ["cherry"] = 3 };

B var dict = new Dictionary<string, int> { ("apple", 1), ("banana", 2), ("cherry", 3) };

C var dict = new Dictionary<string, int> { "apple": 1, "banana": 2, "cherry": 3 };

D var dict = new Dictionary<string, int> { {"apple", 1}, {"banana", 2}, {"cherry", 3} };

💡 Hint

Dictionary initialization uses curly braces with key-value pairs inside another set of braces.

The correct syntax for initializing a dictionary uses curly braces with each key-value pair enclosed in its own braces: { {key, value}, ... }.

❓ optimization

advanced

Which initialization is more efficient for a large list of integers?

You need to initialize a list of 1000 integers from 1 to 1000 in C#. Which option is more efficient in terms of performance and memory?

A var list = new List<int>(Enumerable.Range(1, 1000));

B var list = new List<int>(); list = Enumerable.Range(1, 1000).ToList();

C var list = new List<int> { 1, 2, 3, ..., 1000 }; // manually typed

D var list = new List<int>(); for(int i=1; i<=1000; i++) { list.Add(i); }

💡 Hint

Consider built-in methods that generate sequences efficiently.

Using Enumerable.Range with the List constructor creates the list in one step efficiently. Manually adding or typing all values is less efficient.

🔧 Debug

advanced

What error does this collection initialization cause?

Examine the following C# code snippet: var set = new HashSet { 1, 2, 3, 2, 4 }; What happens when this code runs?

A Compilation error due to duplicate values in initialization.

B The HashSet contains {1, 2, 3, 4} with no error.

C Runtime error due to duplicate values.

D The HashSet contains {1, 2, 3, 2, 4} including duplicates.

💡 Hint

Think about how HashSet handles duplicates.

HashSet automatically ignores duplicate values, so the set contains unique values only without errors.

🧠 Conceptual

expert

Which statement about collection initializers in C# is true?

Select the correct statement about collection initializers in C#.

A Collection initializers automatically sort the collection after initialization.

B Collection initializers can only be used with arrays and lists.

C Collection initializers require the collection to have an Add method.

D Collection initializers can only add primitive types to collections.

💡 Hint

Think about what the compiler uses to add items during initialization.

Collection initializers work by calling the Add method on the collection for each item.