List methods (Add, Remove, Find, Sort) in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add an item to the list.

C Sharp (C#)

List<string> fruits = new List<string>();
fruits.[1]("Apple");

Drag options to blanks, or click blank then click option'

ARemove

BAdd

CFind

DSort

Attempts:

3 left

💡 Hint

Common Mistakes

Using Remove instead of Add will try to delete an item.

Using Find or Sort will not add items.

The Add method adds an item to the end of the list.

2fill in blank

medium

Complete the code to remove an item from the list.

C Sharp (C#)

List<int> numbers = new List<int> {1, 2, 3};
numbers.[1](2);

Drag options to blanks, or click blank then click option'

ARemove

BFind

CAdd

DSort

Attempts:

3 left

💡 Hint

Common Mistakes

Using Add will add an item instead of removing.

Using Find or Sort will not remove items.

The Remove method deletes the first occurrence of the specified item from the list.

3fill in blank

hard

Fix the error in the code to find an item in the list.

C Sharp (C#)

List<string> names = new List<string> {"Anna", "Bob", "Cara"};
string found = names.[1](name => name == "Bob");

Drag options to blanks, or click blank then click option'

AFind

BRemove

CAdd

DSort

Attempts:

3 left

💡 Hint

Common Mistakes

Using Add or Remove will not find items.

Using Sort will reorder the list, not find an item.

The Find method searches for an item that matches the condition given by a lambda expression.

4fill in blank

hard

Fill both blanks to sort the list in ascending order and then remove the first item.

C Sharp (C#)

List<int> values = new List<int> {5, 3, 8};
values.[1]();
values.[2](values[0]);

Drag options to blanks, or click blank then click option'

ASort

BAdd

CRemove

DFind

Attempts:

3 left

💡 Hint

Common Mistakes

Using Add instead of Remove will add an item instead of deleting.

Using Find instead of Sort will not order the list.

First, Sort() arranges the list in ascending order. Then, Remove() deletes the first item.

5fill in blank

hard

Fill all three blanks to add a new item, find it, and then remove it from the list.

C Sharp (C#)

List<string> pets = new List<string> {"Cat", "Dog"};
pets.[1]("Bird");
string foundPet = pets.[2](p => p == "Bird");
pets.[3](foundPet);

Drag options to blanks, or click blank then click option'

AAdd

BFind

CRemove

DSort

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up the order of methods.

Using Sort instead of Find or Remove.

We add "Bird" with Add, find it with Find, then remove it with Remove.

Practice

1. Which List method in C# is used to add a new item to the end of the list?

easy

A. Sort

B. Remove

C. Find

D. Add

Solution

1. Step 1: Understand the purpose of Add

   The Add method appends a new element to the end of a list.

2. Step 2: Compare with other methods

   Remove deletes items, Find searches, and Sort arranges items, so they don't add new items.

3. Final Answer:

   Add -> Option D

4. Quick Check:

   Add method adds items [OK]

Hint: Add puts new items at the list's end [OK]

Common Mistakes:

• Confusing Remove with Add
• Thinking Find adds items
• Assuming Sort adds items

2. Which of the following is the correct syntax to remove the first occurrence of "apple" from a List<string> named fruits?

easy

A. fruits.RemoveAt("apple");

B. fruits.Delete("apple");

C. fruits.Remove("apple");

D. fruits.RemoveItem("apple");

Solution

1. Step 1: Identify the correct method name

   The method to remove an item by value is Remove, so fruits.Remove("apple") is correct.

2. Step 2: Check method parameters and usage

   RemoveAt requires an index, not a string. Delete and RemoveItem are not valid List methods.

3. Final Answer:

   fruits.Remove("apple"); -> Option C

4. Quick Check:

   Remove("apple") removes first matching item [OK]

Hint: Use Remove with the item value to delete it [OK]

Common Mistakes:

• Using RemoveAt with a string argument
• Using non-existent methods like Delete or RemoveItem
• Confusing Remove with Add

3. What will be the output of the following C# code?

var numbers = new List<int> {5, 3, 8, 1};
numbers.Sort();
Console.WriteLine(string.Join(",", numbers));

medium

A. 5,3,8,1

B. 1,3,5,8

C. 8,5,3,1

D. 3,5,1,8

Solution

1. Step 1: Understand what Sort does

   Sort arranges the list items in ascending order.

2. Step 2: Apply Sort to the list

   The list {5, 3, 8, 1} sorted ascending becomes {1, 3, 5, 8}.

3. Final Answer:

   1,3,5,8 -> Option B

4. Quick Check:

   Sort orders numbers ascending [OK]

Hint: Sort arranges numbers from smallest to largest [OK]

Common Mistakes:

• Assuming Sort reverses the list
• Confusing Sort with Find
• Expecting original order after Sort

4. Identify the error in this code snippet:

var fruits = new List<string> {"apple", "banana", "cherry"};
fruits.RemoveAt("banana");

medium

A. RemoveAt expects an index, not a string

B. RemoveAt cannot be used on List<string>

C. RemoveAt removes all matching items

D. RemoveAt adds an item instead of removing

Solution

1. Step 1: Check RemoveAt parameter type

   RemoveAt requires an integer index, but "banana" is a string.

2. Step 2: Understand method behavior

   Using a string causes a compile-time error because the argument type is wrong.

3. Final Answer:

   RemoveAt expects an index, not a string -> Option A

4. Quick Check:

   RemoveAt needs index integer [OK]

Hint: RemoveAt uses index number, not item value [OK]

Common Mistakes:

• Passing item value instead of index to RemoveAt
• Thinking RemoveAt removes all matches
• Confusing RemoveAt with Remove

5. Given a List<int> numbers = new List<int> {4, 7, 2, 9, 3}; which code snippet correctly finds the first number greater than 5 and removes it from the list?

hard

A. var num = numbers.Find(n => n > 5);
numbers.Remove(num);

B. numbers.RemoveAt(numbers.Find(n => n > 5));

C. numbers.Remove(numbers.FindIndex(n => n > 5));

D. numbers.Remove(numbers.Find(n => n < 5));

Solution

1. Step 1: Use Find to get first number > 5

   Find returns the first element matching the condition n > 5, which is 7.

2. Step 2: Remove that number from the list

   Remove(num) deletes the first occurrence of 7 from the list.

3. Final Answer:

   var num = numbers.Find(n => n > 5); numbers.Remove(num); -> Option A

4. Quick Check:

   Find returns item, Remove deletes it [OK]

Hint: Find returns item; Remove deletes that item [OK]

Common Mistakes:

• Passing Find result directly to RemoveAt (wrong type)
• Using FindIndex result with Remove (expects item, not index)
• Searching for wrong condition (n < 5 instead of n > 5)