Select clause projection in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this LINQ Select projection?

Consider the following C# code using LINQ to project a list of numbers to their squares. What will be printed to the console?

C Sharp (C#)

using System;
using System.Linq;

class Program {
    static void Main() {
        int[] numbers = {1, 2, 3, 4};
        var squares = numbers.Select(x => x * x);
        foreach(var sq in squares) {
            Console.Write(sq + " ");
        }
    }
}

A 1 2 3 4

B System.Linq.Enumerable+WhereSelectArrayIterator`2[System.Int32,System.Int32]

C 1 4 9 16

D Compilation error

💡 Hint

Remember that Select projects each element to a new value.

The Select method applies the lambda x => x * x to each element, producing their squares: 1, 4, 9, 16.

❓ Predict Output

intermediate

What does this Select projection produce?

Given this code snippet, what will be the output?

C Sharp (C#)

using System;
using System.Linq;

class Program {
    static void Main() {
        string[] words = {"apple", "banana", "cherry"};
        var firstChars = words.Select(w => w[0]);
        foreach(var ch in firstChars) {
            Console.Write(ch + "-");
        }
    }
}

A a-b-c-

B a b c

C Compilation error

D apple-banana-cherry-

💡 Hint

Select projects each string to its first character.

Each word is projected to its first character: 'a', 'b', 'c', printed with dashes.

❓ Predict Output

advanced

What is the output of this Select projection with anonymous types?

What will this program print?

C Sharp (C#)

using System;
using System.Linq;

class Program {
    static void Main() {
        var people = new[] {
            new { Name = "Alice", Age = 30 },
            new { Name = "Bob", Age = 25 }
        };
        var names = people.Select(p => new { p.Name, IsAdult = p.Age >= 18 });
        foreach(var n in names) {
            Console.Write($"{n.Name}:{n.IsAdult} ");
        }
    }
}

A Alice:30 Bob:25

B Alice:True Bob:True

C Compilation error

D System.Object System.Object

💡 Hint

Select creates new anonymous objects with Name and IsAdult properties.

Each person is projected to an anonymous object with Name and a boolean IsAdult indicating if Age >= 18.

❓ Predict Output

advanced

What error does this Select projection cause?

What happens when you run this code?

C Sharp (C#)

using System;
using System.Linq;

class Program {
    static void Main() {
        string[] words = {"one", null, "three"};
        var lengths = words.Select(w => w.Length);
        foreach(var len in lengths) {
            Console.Write(len + " ");
        }
    }
}

A System.NullReferenceException at runtime

B 3 5

C 3 0 5

D Compilation error

💡 Hint

One element is null, so accessing Length causes an error.

The Select tries to access Length on a null string, causing a NullReferenceException at runtime.

🧠 Conceptual

expert

How many items are in the resulting sequence after this Select projection?

Given this code, how many elements will the 'result' sequence contain?

C Sharp (C#)

using System.Linq;

var numbers = new int[] { 2, 4, 6, 8 };
var result = numbers.Select(x => x / 2).Where(x => x > 2);

A 4

B 1

C 3

D 2

💡 Hint

First Select divides each number by 2, then Where filters those greater than 2.

Dividing numbers by 2 gives {1, 2, 3, 4}. Filtering > 2 leaves {3, 4}, so 2 elements remain.