LINQ query syntax in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this LINQ query?

Consider the following C# code using LINQ query syntax. What will be printed?

C Sharp (C#)

using System;
using System.Linq;

class Program {
    static void Main() {
        int[] numbers = { 1, 2, 3, 4, 5 };
        var query = from n in numbers
                    where n % 2 == 0
                    select n * n;
        foreach (var item in query) {
            Console.Write(item + " ");
        }
    }
}

A 2 4

B 1 9 25

C 4 16

D 1 4 9 16 25

💡 Hint

Look at the where clause filtering even numbers, then the select projects squares.

The query filters numbers to only even ones (2 and 4), then selects their squares (4 and 16). So output is "4 16 ".

🧠 Conceptual

intermediate

Which LINQ query syntax correctly selects names starting with 'J'?

Given a list of names, which LINQ query syntax correctly selects only those starting with the letter 'J'?

C Sharp (C#)

string[] names = { "John", "Alice", "James", "Bob" };

A var result = from name in names select name where name.StartsWith("J");

B var result = from name in names where name.StartsWith("J") select name;

C var result = from name in names select name if name.StartsWith("J");

D var result = from name in names where name.Contains("J") select name;

💡 Hint

Remember the where clause comes before select in query syntax.

Option B correctly uses where to filter names starting with 'J' before selecting them. Option B and C have syntax errors. Option B filters names containing 'J' anywhere, not just starting with 'J'.

🔧 Debug

advanced

What error does this LINQ query produce?

Examine the following LINQ query code. What error will it cause when compiled?

C Sharp (C#)

int[] nums = {1, 2, 3};
var q = from n in nums
        where n > 1
        select n > 2 ? n : ;

A SyntaxError: incomplete ternary operator

B TypeError: cannot convert bool to int

C Runtime NullReferenceException

D No error, outputs 3

💡 Hint

Look carefully at the ternary operator syntax in the select clause.

The ternary operator is incomplete because the 'else' part after ':' is missing, causing a syntax error.

❓ Predict Output

advanced

What is the output of this LINQ query with ordering?

What will be printed by this C# program using LINQ query syntax with ordering?

C Sharp (C#)

using System;
using System.Linq;

class Program {
    static void Main() {
        string[] fruits = { "apple", "banana", "cherry", "date" };
        var query = from f in fruits
                    orderby f.Length descending, f
                    select f;
        foreach (var fruit in query) {
            Console.Write(fruit + " ");
        }
    }
}

A date apple banana cherry

B banana cherry date apple

C cherry banana apple date

D banana cherry apple date

💡 Hint

Order by length descending, then alphabetically ascending.

Fruits ordered by length descending: banana(6), cherry(6), apple(5), date(4). For ties (banana, cherry), order alphabetically ascending: banana before cherry.

🧠 Conceptual

expert

How many items are in the resulting collection?

Given this LINQ query, how many items will the result collection contain?

C Sharp (C#)

int[] values = { 2, 4, 6, 8, 10 };
var result = from v in values
             where v % 4 == 0
             select v / 2;

A 2

B 3

C 4

D 5

💡 Hint

Check which numbers in the array are divisible by 4.

Only 4 and 8 are divisible by 4, so the query selects 2 items (4/2=2 and 8/2=4).