OrderBy and sorting in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this OrderBy example?

Consider the following C# code that sorts a list of integers using OrderBy. What will be printed to the console?

C Sharp (C#)

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

class Program {
    static void Main() {
        List<int> numbers = new() { 5, 3, 8, 1 };
        var sorted = numbers.OrderBy(n => n);
        foreach(var num in sorted) {
            Console.Write(num + " ");
        }
    }
}

A 1 3 5 8

B 8 5 3 1

C 5 3 8 1

D 3 5 1 8

💡 Hint

OrderBy sorts elements in ascending order by default.

OrderBy sorts the list from smallest to largest. The original list is {5,3,8,1}, so sorted ascending is {1,3,5,8}.

❓ Predict Output

intermediate

What is the output when sorting strings by length?

This code sorts a list of strings by their length using OrderBy. What will be printed?

C Sharp (C#)

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

class Program {
    static void Main() {
        List<string> words = new() { "apple", "dog", "banana", "cat" };
        var sorted = words.OrderBy(w => w.Length);
        foreach(var w in sorted) {
            Console.Write(w + " ");
        }
    }
}

A cat dog apple banana

B apple dog banana cat

C banana apple dog cat

D dog cat apple banana

💡 Hint

OrderBy sorts by the key selector, here the string length.

Strings sorted by length ascending: "dog" (3), "cat" (3), "apple" (5), "banana" (6). Since "dog" and "cat" have same length, their original order is preserved.

❓ Predict Output

advanced

What is the output of this OrderByDescending with complex objects?

Given this code that sorts a list of Person objects by Age descending, what will be printed?

C Sharp (C#)

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

record Person(string Name, int Age);

class Program {
    static void Main() {
        List<Person> people = new() {
            new("Alice", 30),
            new("Bob", 25),
            new("Charlie", 35)
        };
        var sorted = people.OrderByDescending(p => p.Age);
        foreach(var p in sorted) {
            Console.Write(p.Name + " ");
        }
    }
}

A Charlie Bob Alice

B Charlie Alice Bob

C Bob Alice Charlie

D Alice Bob Charlie

💡 Hint

OrderByDescending sorts from largest to smallest by the key.

Ages are 30, 25, 35. Descending order is 35 (Charlie), 30 (Alice), 25 (Bob).

❓ Predict Output

advanced

What is the output of this chained OrderBy and ThenBy?

This code sorts a list of tuples first by the first item ascending, then by the second item descending. What is printed?

C Sharp (C#)

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

class Program {
    static void Main() {
        var list = new List<(int, int)>{ (1, 2), (1, 3), (2, 1), (2, 2) };
        var sorted = list.OrderBy(x => x.Item1).ThenByDescending(x => x.Item2);
        foreach(var t in sorted) {
            Console.Write($"({t.Item1},{t.Item2}) ");
        }
    }
}

A (1,3) (1,2) (2,2) (2,1)

B (1,2) (1,3) (2,1) (2,2)

C (2,2) (2,1) (1,3) (1,2)

D (2,1) (2,2) (1,2) (1,3)

💡 Hint

OrderBy sorts by first item ascending, ThenByDescending sorts by second item descending within groups.

Group by first item: 1 and 2. For 1: (1,3) then (1,2). For 2: (2,2) then (2,1).

🧠 Conceptual

expert

Which option causes a runtime error when sorting with OrderBy?

Given a list of objects, which code snippet will cause a runtime exception when using OrderBy in C#?

A list.OrderBy(x => x.GetHashCode())

B list.OrderBy(x => x.PropertyThatExists)

C list.OrderBy(x => x.NonExistentProperty)

D list.OrderBy(x => x.ToString())

💡 Hint

Accessing a property that does not exist will cause an error at runtime.

Option C tries to access a property that does not exist on the objects, causing a runtime exception (usually a RuntimeBinderException or similar). Other options use valid properties or methods.