Immediate execution methods in C Sharp (C#) - Mini Project: Build & Apply

Immediate Execution Methods in C#

📖 Scenario: You are working on a small program that manages a list of book titles in a library. You want to understand how to use immediate execution methods to get results right away from your list.

🎯 Goal: Build a simple C# program that creates a list of book titles, sets a filter condition, uses an immediate execution method to get filtered results, and then prints those results.

📋 What You'll Learn

Create a list of strings called books with exact titles

Create an integer variable minLength to set the minimum title length

Use the Where method with ToList() to filter books with titles longer than minLength

Print each filtered book title using a foreach loop

💡 Why This Matters

🌍 Real World

Filtering lists immediately is useful in apps where you want quick results, like showing books longer than a certain title length in a library app.

💼 Career

Understanding immediate execution methods is important for C# developers working with data collections and LINQ queries to write efficient and clear code.

1

Create the list of book titles

Create a list of strings called books with these exact titles: "C# Basics", "LINQ in Action", "ASP.NET Core", "Entity Framework", "Blazor Guide".

C Sharp (C#)

// Create the list of book titles
// Your code here

Hint

Use new List { ... } to create the list with the exact titles.

2

Set the minimum title length

Create an integer variable called minLength and set it to 10.

C Sharp (C#)

using System.Collections.Generic;

List books = new List { "C# Basics", "LINQ in Action", "ASP.NET Core", "Entity Framework", "Blazor Guide" };

// Create the integer variable minLength and set it to 10
// Your code here

Hint

Use int minLength = 10; to create the variable.

3

Filter books with immediate execution

Use the Where method with ToList() to create a new list called longBooks that contains only books with titles longer than minLength. Use book as the lambda variable.

C Sharp (C#)

using System.Collections.Generic;
using System.Linq;

List books = new List { "C# Basics", "LINQ in Action", "ASP.NET Core", "Entity Framework", "Blazor Guide" };

int minLength = 10;

// Create longBooks using Where and ToList to filter books with length > minLength
// Your code here

Hint

Use books.Where(book => book.Length > minLength).ToList() to get the filtered list immediately.

4

Print the filtered book titles

Use a foreach loop with variable book to print each title in longBooks using Console.WriteLine(book);.

C Sharp (C#)

using System;
using System.Collections.Generic;
using System.Linq;

List books = new List { "C# Basics", "LINQ in Action", "ASP.NET Core", "Entity Framework", "Blazor Guide" };

int minLength = 10;

List longBooks = books.Where(book => book.Length > minLength).ToList();

// Use foreach to print each book in longBooks
// Your code here

Hint

Use foreach (string book in longBooks) { Console.WriteLine(book); } to print each title.

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