Immediate execution methods in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to immediately execute the LINQ query and get the count of even numbers.

C Sharp (C#)

int[] numbers = {1, 2, 3, 4, 5};
int evenCount = numbers.Where(n => n % 2 == 0).[1]();

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

ASelect

BCount

CWhere

DOrderBy

Attempts:

3 left

💡 Hint

Common Mistakes

Using Select() instead of Count(), which does not return a count.

Using Where() again, which just filters but does not execute.

The Count() method immediately executes the query and returns the number of elements that satisfy the condition.

2fill in blank

medium

Complete the code to immediately execute the LINQ query and convert the result to a list.

C Sharp (C#)

string[] fruits = {"apple", "banana", "cherry"};
var fruitList = fruits.Where(f => f.Contains('a')).[1]();

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

AToArray

BOrderBy

CSelect

DToList

Attempts:

3 left

💡 Hint

Common Mistakes

Using ToArray() which returns an array, not a List.

Using Select() which does not execute the query immediately.

The ToList() method immediately executes the query and returns a List containing the filtered elements.

3fill in blank

hard

Fix the error in the code to immediately get the first element that matches the condition.

C Sharp (C#)

List<int> scores = new() { 70, 85, 90 };
int topScore = scores.Where(s => s > 80).[1]();

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

AFirst

BFirstOrDefault

CSingle

DLast

Attempts:

3 left

💡 Hint

Common Mistakes

Using Single() which expects exactly one element.

Using Last() which returns the last matching element.

The First() method immediately executes the query and returns the first element that matches the condition. It throws an error if no element is found.

4fill in blank

hard

Fill both blanks to immediately get the maximum score from the list.

C Sharp (C#)

List<int> scores = new() { 55, 78, 92, 88 };
int maxScore = scores.[1](s => s).[2]();

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

AMax

BMin

COrderByDescending

DOrderBy

Attempts:

3 left

💡 Hint

Common Mistakes

Using Min() instead of Max().

Using OrderBy() which sorts ascending.

OrderByDescending() sorts the scores from highest to lowest, and Max() returns the maximum value immediately.

5fill in blank

hard

Fill all three blanks to immediately create a dictionary of words and their lengths for words longer than 3 characters.

C Sharp (C#)

string[] words = {"cat", "elephant", "dog", "horse"};
var wordLengths = words.Where(w => w.Length > [1]).ToDictionary([2], [3]);

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

A3

Bw

Cw.Length

D4

Attempts:

3 left

💡 Hint

Common Mistakes

Using 4 instead of 3 for the length filter.

Using incorrect key or value selectors in ToDictionary().

The code filters words longer than 3 characters, then creates a dictionary with the word as the key and its length as the value.

Practice

1. Which of the following methods in C# causes immediate execution of a LINQ query?

easy

A. ToList()

B. Where()

C. Select()

D. OrderBy()

Solution

1. Step 1: Understand deferred vs immediate execution

   Methods like Where(), Select(), and OrderBy() only build the query and do not execute it immediately.

2. Step 2: Identify immediate execution methods

   ToList() forces the query to run and returns a list immediately.

3. Final Answer:

   ToList() -> Option A

4. Quick Check:

   Immediate execution = ToList() [OK]

Hint: Immediate methods like ToList() run queries right away [OK]

Common Mistakes:

• Confusing deferred methods like Where() as immediate
• Thinking Select() executes query immediately
• Assuming OrderBy() runs query instantly

2. Which of the following is the correct syntax to immediately get the count of elements in a LINQ query numbers?

easy

A. int count = numbers.Count;

B. int count = Count(numbers);

C. int count = numbers.Count();

D. int count = numbers.Count[];

Solution

1. Step 1: Recognize Count() as a method

   In LINQ, Count() is a method that must be called with parentheses to execute immediately.

2. Step 2: Check syntax correctness

   numbers.Count() is the correct syntax; Count without parentheses is a property, which does not exist here.

3. Final Answer:

   int count = numbers.Count(); -> Option C

4. Quick Check:

   Count() method needs parentheses [OK]

Hint: Count() always needs parentheses to execute immediately [OK]

Common Mistakes:

• Using Count without parentheses
• Trying to call Count as a standalone function
• Using invalid syntax like Count[]

3. What is the output of the following code?

var numbers = new List<int> {1, 2, 3, 4};
var result = numbers.Where(n => n > 2).Count();
Console.WriteLine(result);

medium

A. 0

B. 3

C. 4

D. 2

Solution

1. Step 1: Filter numbers greater than 2

   The Where method filters numbers: 3 and 4 satisfy the condition, so filtered list is [3,4].

2. Step 2: Count the filtered elements

   Count() returns the number of elements in the filtered list, which is 2.

3. Final Answer:

   2 -> Option D

4. Quick Check:

   Count of numbers > 2 = 2 [OK]

Hint: Count() after Where() counts filtered items immediately [OK]

Common Mistakes:

• Counting original list length instead of filtered
• Confusing Count() with deferred execution
• Assuming Where() returns count directly

4. Identify the error in this code snippet:

var list = new List<string> {"apple", "banana"};
var first = list.First;
Console.WriteLine(first);

medium

A. Missing parentheses after First method

B. List initialization syntax is wrong

C. Console.WriteLine cannot print strings

D. First method does not exist on List

Solution

1. Step 1: Check usage of First method

   First is a method and requires parentheses to execute immediately.

2. Step 2: Identify syntax error

   Code uses list.First without parentheses, which causes a compile-time error.

3. Final Answer:

   Missing parentheses after First method -> Option A

4. Quick Check:

   First() needs () to run immediately [OK]

Hint: Always add () when calling immediate execution methods [OK]

Common Mistakes:

• Forgetting parentheses on First()
• Thinking First is a property
• Misunderstanding List initialization syntax

5. Given a list of integers, how can you immediately get a list of only even numbers using LINQ and immediate execution methods?

hard

A. var evens = numbers.Where(n => n % 2 == 0);

B. var evens = numbers.Where(n => n % 2 == 0).ToList();

C. var evens = numbers.Select(n => n % 2 == 0).ToList();

D. var evens = numbers.ToList().Where(n => n % 2 == 0);

Solution

1. Step 1: Filter even numbers with Where()

   Where(n => n % 2 == 0) filters the list to only even numbers.

2. Step 2: Use ToList() for immediate execution

   Calling ToList() after filtering runs the query immediately and returns a list of even numbers.

3. Final Answer:

   var evens = numbers.Where(n => n % 2 == 0).ToList(); -> Option B

4. Quick Check:

   Filter then ToList() = immediate even list [OK]

Hint: Chain Where() then ToList() for immediate filtered list [OK]

Common Mistakes:

• Not calling ToList() to force immediate execution
• Calling ToList() before Where(), which returns full list
• Using Select() incorrectly to filter