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

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this LINQ method syntax code?

Consider the following C# code using LINQ method syntax. What will be printed to the console?

C Sharp (C#)

var numbers = new List<int> { 1, 2, 3, 4, 5 };
var result = numbers.Where(n => n % 2 == 0).Select(n => n * n);
foreach(var num in result) {
    Console.Write(num + " ");
}

A 2 4

B 1 9 25

C 4 16

D 1 2 3 4 5

💡 Hint

Think about which numbers are even and what happens to them in the Select step.

The code filters the list to only even numbers (2 and 4), then squares each. So output is 4 and 16.

🧠 Conceptual

intermediate

Which LINQ method syntax expression counts elements greater than 10?

You have a list of integers. Which of the following LINQ method syntax expressions correctly counts how many elements are greater than 10?

A numbers.Select(n => n > 10).Count()

B numbers.Count(n => n > 10)

C numbers.Where(n => n > 10).Count()

D numbers.Count().Where(n => n > 10)

💡 Hint

Count can take a condition directly or you can filter first then count.

Option B uses Count with a predicate, which counts elements matching the condition directly. Option B also works but is less efficient. Option B counts all elements because Select returns booleans. Option B is invalid syntax.

🔧 Debug

advanced

What error does this LINQ method syntax code produce?

Examine the code below. What error will it cause when compiled or run?

C Sharp (C#)

var words = new List<string> { "apple", "banana", "cherry" };
var result = words.Select(word => word.Length > 5 ? word : );
foreach(var w in result) {
    Console.WriteLine(w);
}

A InvalidOperationException: Sequence contains no elements

B NullReferenceException at runtime

C No error, prints all words

D SyntaxError: Missing expression after ':' in ternary operator

💡 Hint

Look carefully at the ternary operator syntax inside Select.

The ternary operator requires both 'true' and 'false' expressions. Here, the false part is missing, causing a syntax error.

❓ Predict Output

advanced

What is the output of this LINQ method syntax with grouping?

Given the code below, what will be printed to the console?

C Sharp (C#)

var fruits = new List<string> { "apple", "apricot", "banana", "blueberry", "cherry" };
var groups = fruits.GroupBy(f => f[0]);
foreach(var group in groups) {
    Console.Write(group.Key + ":");
    Console.WriteLine(string.Join(",", group));
}

A

a:apple,apricot
b:banana,blueberry
c:cherry

B

apple:apricot
banana:blueberry
cherry:

C

a:apple
apricot
b:banana
blueberry
c:cherry

D

a:apple,banana
b:apricot,blueberry
c:cherry

💡 Hint

GroupBy groups by the first letter of each fruit.

The fruits are grouped by their first letter: 'a' group has apple and apricot, 'b' group has banana and blueberry, 'c' group has cherry. The output prints each group key and its items separated by commas.

❓ Predict Output

expert

What is the value of 'result' after this LINQ method syntax chain?

Analyze the code below. What is the value of the variable 'result' after execution?

C Sharp (C#)

var data = new List<int> { 3, 6, 9, 12, 15 };
var result = data.Aggregate(1, (acc, val) => val % 3 == 0 ? acc * val : acc);

A 29160

B 0

C 1

D 45

💡 Hint

Aggregate starts with 1 and multiplies values divisible by 3.

All numbers in data are divisible by 3, so the accumulator multiplies all: 1*3=3, 3*6=18, 18*9=162, 162*12=1944, 1944*15=29160.