LINQ query syntax in C Sharp (C#) - Mini Project: Build & Apply

LINQ Query Syntax

📖 Scenario: You work in a bookstore. You have a list of books with their titles and prices. You want to find all books that cost less than $20 to recommend to budget readers.

🎯 Goal: Build a C# program that uses LINQ query syntax to select books priced below $20 from a list and display their titles.

📋 What You'll Learn

Create a list of books with exact titles and prices

Create a price limit variable set to 20

Use LINQ query syntax with from, where, and select to find books cheaper than the price limit

Print the titles of the selected books

💡 Why This Matters

🌍 Real World

Filtering and selecting data from collections is common in apps like online stores, libraries, and inventory systems.

💼 Career

Knowing LINQ query syntax helps you write clear and efficient data queries in C# jobs involving data processing and software development.

1

Create the list of books

Create a list of books called books with these exact entries: ("C# Basics", 15), ("Advanced C#", 25), ("LINQ in Action", 18), ("ASP.NET Core", 30), ("Entity Framework", 12). Use a list of tuples with string and int types.

C Sharp (C#)

# Create the list of books with exact titles and prices
// Your code here

Hint

Use List<(string, int)> and add the tuples exactly as shown.

2

Set the price limit

Create an integer variable called priceLimit and set it to 20.

C Sharp (C#)

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        List books = new List
        {
            ("C# Basics", 15),
            ("Advanced C#", 25),
            ("LINQ in Action", 18),
            ("ASP.NET Core", 30),
            ("Entity Framework", 12)
        };
        // Create priceLimit variable and set to 20
        // Your code here
    }
}

Hint

Use int priceLimit = 20; inside the Main method.

3

Write the LINQ query

Use LINQ query syntax to create a variable called cheapBooks that selects the Title of books from books where the Price is less than priceLimit. Use from, where, and select keywords.

C Sharp (C#)

using System.Linq;
        var cheapBooks = from book in books
                         where book.Price < priceLimit
                         select book.Title;
        // Print each title in cheapBooks

Hint

Use var cheapBooks = from book in books where book.Price < priceLimit select book.Title;

4

Print the selected book titles

Use a foreach loop with variable title to iterate over cheapBooks and print each title on its own line using Console.WriteLine.

C Sharp (C#)

Hint

Use foreach (var title in cheapBooks) { Console.WriteLine(title); } to print each title.

Practice

1. What does the LINQ query syntax in C# primarily help you do with collections?

easy

A. Write low-level assembly code

B. Create new classes and objects

C. Manage memory allocation manually

D. Filter, sort, group, and select data in a readable way

Solution

1. Step 1: Understand LINQ purpose

   LINQ query syntax is designed to work with collections to filter, sort, group, and select data.

2. Step 2: Compare options

   Options B, C, and D describe unrelated programming tasks, not LINQ's purpose.

3. Final Answer:

   Filter, sort, group, and select data in a readable way -> Option D

4. Quick Check:

   LINQ = Data querying [OK]

Hint: LINQ reads like English to query collections [OK]

Common Mistakes:

• Confusing LINQ with object creation
• Thinking LINQ manages memory
• Assuming LINQ writes low-level code

2. Which of the following is the correct basic syntax to start a LINQ query in C#?

easy

A. var result = select item from collection;

B. var result = collection from item select;

C. var result = from item in collection select item;

D. var result = item select from collection;

Solution

1. Step 1: Recall LINQ query syntax structure

   The correct LINQ query starts with 'from', then the range variable, then 'in' and the collection, followed by 'select'.

2. Step 2: Match options to syntax

   Only var result = from item in collection select item; follows this correct order: 'from item in collection select item;'. Others have wrong order or keywords.

3. Final Answer:

   var result = from item in collection select item; -> Option C

4. Quick Check:

   from ... in ... select ... [OK]

Hint: LINQ starts with 'from' then 'in' then 'select' [OK]

Common Mistakes:

• Swapping 'from' and 'select' keywords
• Omitting 'in' keyword
• Incorrect order of clauses

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

int[] numbers = {1, 2, 3, 4, 5};
var evens = from n in numbers
            where n % 2 == 0
            select n;
foreach(var num in evens) {
    Console.Write(num + " ");
}

medium

A. 1 3 5

B. 2 4

C. 1 2 3 4 5

D. No output

Solution

1. Step 1: Analyze the LINQ query filtering condition

   The query selects numbers where n % 2 == 0, meaning even numbers only.

2. Step 2: Identify even numbers in the array

   From {1,2,3,4,5}, even numbers are 2 and 4.

3. Final Answer:

   2 4 -> Option B

4. Quick Check:

   Filter evens = 2 4 [OK]

Hint: Look for 'where' condition filtering evens [OK]

Common Mistakes:

• Selecting odd numbers by mistake
• Ignoring the 'where' clause
• Assuming all numbers are selected

4. Identify the error in the following LINQ query syntax:

var result = from x collection
             where x > 10
             select x;

medium

A. Missing 'in' keyword between 'x' and 'collection'

B. Incorrect 'where' clause syntax

C. 'select' keyword should come before 'where'

D. Variable 'x' is not declared

Solution

1. Step 1: Check the 'from' clause syntax

   The 'from' clause must have 'from variable in collection'. Here 'in' is missing.

2. Step 2: Verify other clauses

   The 'where' and 'select' clauses are correctly placed and syntactically valid.

3. Final Answer:

   Missing 'in' keyword between 'x' and 'collection' -> Option A

4. Quick Check:

   'from x in collection' needed [OK]

Hint: Check 'from' clause for 'in' keyword [OK]

Common Mistakes:

• Omitting 'in' keyword in 'from' clause
• Misordering 'where' and 'select'
• Assuming variable declaration needed

5. Given a list of strings words, which LINQ query syntax correctly selects words starting with 'a' and orders them alphabetically?

hard

A. var query = from w in words where w.StartsWith("a") orderby w select w;

B. var query = from w in words orderby w where w.StartsWith("a") select w;

C. var query = from w in words select w where w.StartsWith("a") orderby w;

D. var query = from w in words select w orderby w where w.StartsWith("a");

Solution

1. Step 1: Understand LINQ clause order

   The correct order is 'from', then 'where', then 'orderby', then 'select'. var query = from w in words where w.StartsWith("a") orderby w select w; follows this order.

2. Step 2: Verify filtering and ordering

   var query = from w in words where w.StartsWith("a") orderby w select w; filters words starting with 'a' and orders them alphabetically before selecting.

3. Final Answer:

   var query = from w in words where w.StartsWith("a") orderby w select w; -> Option A

4. Quick Check:

   where before orderby in LINQ [OK]

Hint: Remember clause order: from, where, orderby, select [OK]

Common Mistakes:

• Placing 'orderby' before 'where'
• Misplacing 'select' clause
• Using wrong method syntax inside query