List methods (Add, Remove, Find, Sort) in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this C# code using List.Add and List.Remove?

Consider the following C# code snippet:

using System;
using System.Collections.Generic;

class Program {
    static void Main() {
        List<string> fruits = new List<string>();
        fruits.Add("Apple");
        fruits.Add("Banana");
        fruits.Add("Cherry");
        fruits.Remove("Banana");
        foreach (var fruit in fruits) {
            Console.Write(fruit + " ");
        }
    }
}

What will be printed when this code runs?

C Sharp (C#)

using System;
using System.Collections.Generic;

class Program {
    static void Main() {
        List<string> fruits = new List<string>();
        fruits.Add("Apple");
        fruits.Add("Banana");
        fruits.Add("Cherry");
        fruits.Remove("Banana");
        foreach (var fruit in fruits) {
            Console.Write(fruit + " ");
        }
    }
}

A Apple Banana Cherry

B Banana Cherry

C Apple Cherry

D Apple Cherry Banana

💡 Hint

Remember that Remove deletes the first matching item from the list.

The code adds three fruits to the list: Apple, Banana, and Cherry. Then it removes "Banana". So the list contains "Apple" and "Cherry". The foreach loop prints these with spaces.

❓ Predict Output

intermediate

What is the output of this C# code using List.Find?

Look at this C# code:

using System;
using System.Collections.Generic;

class Program {
    static void Main() {
        List<int> numbers = new List<int> { 10, 20, 30, 40, 50 };
        int found = numbers.Find(x => x > 25);
        Console.WriteLine(found);
    }
}

What number will be printed?

C Sharp (C#)

using System;
using System.Collections.Generic;

class Program {
    static void Main() {
        List<int> numbers = new List<int> { 10, 20, 30, 40, 50 };
        int found = numbers.Find(x => x > 25);
        Console.WriteLine(found);
    }
}

A 10

B 20

C 40

D 30

💡 Hint

Find returns the first element that matches the condition.

The list has numbers 10, 20, 30, 40, 50. The condition is > 25. The first number greater than 25 is 30, so 30 is printed.

❓ Predict Output

advanced

What is the output after sorting this list of strings?

Examine this C# code:

using System;
using System.Collections.Generic;

class Program {
    static void Main() {
        List<string> names = new List<string> { "Zoe", "Anna", "Mike" };
        names.Sort();
        foreach (var name in names) {
            Console.Write(name + " ");
        }
    }
}

What will be printed?

C Sharp (C#)

using System;
using System.Collections.Generic;

class Program {
    static void Main() {
        List<string> names = new List<string> { "Zoe", "Anna", "Mike" };
        names.Sort();
        foreach (var name in names) {
            Console.Write(name + " ");
        }
    }
}

A Mike Anna Zoe

B Anna Mike Zoe

C Zoe Anna Mike

D Mike Zoe Anna

💡 Hint

Sort arranges strings in alphabetical order.

The list is sorted alphabetically: Anna, Mike, Zoe. The foreach prints them in this order.

❓ Predict Output

advanced

What error does this code raise when removing an item not in the list?

Consider this C# code:

using System;
using System.Collections.Generic;

class Program {
    static void Main() {
        List<int> nums = new List<int> { 1, 2, 3 };
        bool removed = nums.Remove(5);
        Console.WriteLine(removed);
    }
}

What will be printed or what error occurs?

C Sharp (C#)

using System;
using System.Collections.Generic;

class Program {
    static void Main() {
        List<int> nums = new List<int> { 1, 2, 3 };
        bool removed = nums.Remove(5);
        Console.WriteLine(removed);
    }
}

A False

B ArgumentOutOfRangeException

C True

D NullReferenceException

💡 Hint

Remove returns a boolean indicating success or failure.

Since 5 is not in the list, Remove returns false. No exception is thrown.

🧠 Conceptual

expert

How many items remain after this sequence of List operations?

Given this C# code:

using System;
using System.Collections.Generic;

class Program {
    static void Main() {
        List<int> data = new List<int> { 5, 10, 15, 20, 25 };
        data.RemoveAll(x => x % 10 == 0);
        data.Add(30);
        data.Sort();
        data.Remove(15);
        Console.WriteLine(data.Count);
    }
}

How many items will be printed?

C Sharp (C#)

using System;
using System.Collections.Generic;

class Program {
    static void Main() {
        List<int> data = new List<int> { 5, 10, 15, 20, 25 };
        data.RemoveAll(x => x % 10 == 0);
        data.Add(30);
        data.Sort();
        data.Remove(15);
        Console.WriteLine(data.Count);
    }
}

A 3

B 4

C 5

D 2

💡 Hint

Track each operation carefully: removal, addition, sorting, then removal again.

Initial list: 5,10,15,20,25
RemoveAll removes numbers divisible by 10 (10 and 20) → 5,15,25
Add 30 → 5,15,25,30
Sort → 5,15,25,30
Remove 15 → 5,25,30
Count is 3.