First, Single, and their OrDefault variants in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get the first number from the list.

C Sharp (C#)

var numbers = new List<int> {1, 2, 3};
int first = numbers.[1]();

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

AFirst

BSingle

CLast

DCount

Attempts:

3 left

💡 Hint

Common Mistakes

Using Single() when there are multiple elements causes an error.

The First() method returns the first element in the list.

2fill in blank

medium

Complete the code to get the single element from the list that equals 5.

C Sharp (C#)

var numbers = new List<int> {5};
int single = numbers.[1](n => n == 5);

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

AFirst

BLast

CSingle

DWhere

Attempts:

3 left

💡 Hint

Common Mistakes

Using First() may return the first match even if there are multiple.

The Single() method returns the only element that matches the condition. It throws an error if there are zero or more than one matches.

3fill in blank

hard

Fix the error in the code to safely get the first element or default if none exists.

C Sharp (C#)

var emptyList = new List<int>();
int firstOrDefault = emptyList.[1]();

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

ASingleOrDefault

BFirstOrDefault

CFirst

DSingle

Attempts:

3 left

💡 Hint

Common Mistakes

Using First() causes an exception if the list is empty.

FirstOrDefault() returns the first element or the default value (0 for int) if the list is empty, avoiding exceptions.

4fill in blank

hard

Fill both blanks to get the single element matching the condition or default if none exists.

C Sharp (C#)

var numbers = new List<int> {1, 2, 3};
int result = numbers.[1](n => n == 2).[2]();

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

AWhere

BFirstOrDefault

CSingleOrDefault

DFirst

Attempts:

3 left

💡 Hint

Common Mistakes

Using SingleOrDefault() directly may throw if multiple matches.

Use Where() to filter, then FirstOrDefault() to get the first matching element or default if none.

5fill in blank

hard

Fill all three blanks to get the single element matching the condition or default if none exists, using method chaining.

C Sharp (C#)

var words = new List<string> {"apple", "banana", "cherry"};
string word = words.[1](w => w.StartsWith("b")).[2]().[3]();

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

AWhere

BSingleOrDefault

CToList

DFirstOrDefault

Attempts:

3 left

💡 Hint

Common Mistakes

Skipping ToList() may cause errors if multiple matches exist.

Filter with Where(), convert to list with ToList(), then get single or default with SingleOrDefault().