List<T> methods
Learn to manage List<T> with Remove, Contains and Count.
List<T> methods
The List<T> collection offers several useful methods to manage items. Remove(value) deletes the first item equal to the given value; Contains(value) checks whether the item exists and returns a bool.
The Count property gives the number of items; if Remove succeeds, this number drops by one. Example: nums.Remove(10); removes the value 10 from the list.
RemoveAt and indexer
RemoveAt(index) deletes the item at a specific index; it is useful when you want to delete by position rather than value. nums.RemoveAt(0) removes the first item.
You can access items in the list with the indexer: nums[0] gives the first item. As with arrays, indices start at 0; an invalid index raises ArgumentOutOfRangeException.
Exercise Remove an item and count
Start with List<int> nums = new List<int>() { 5, 10, 15 };. Remove the value 10 with nums.Remove(10). Then print nums.Count with Console.WriteLine.
Show example solution
Remove 10 with nums.Remove(10);, then print the count with Console.WriteLine(nums.Count);.
Example solution:
using System;
using System.Collections.Generic;
class Program
{
static void Main()
{
List<int> nums = new List<int>() { 5, 10, 15 };
// Remove 10 and print the count
nums.Remove(10);
Console.WriteLine(nums.Count);
}
}Test yourself
-
Remove call
List<int> nums = new List<int>() { 5, 10, 15 }; ____ Console.WriteLine(nums.Count);Show answer
List<int> nums = new List<int>() { 5, 10, 15 }; nums.Remove(10); Console.WriteLine(nums.Count); -
What does Contains print?
List<string> names = new List<string>() { "Ayşe", "Alex" }; bool has = names.Contains("Ayşe"); Console.WriteLine(has);- false
- 0
- true
- Ayşe
Show answer
true — Correct. "Ayşe" is in the list; Contains returns true.
-
Match each method to its meaning
- nums.Remove(5)
- Removes by value
- nums.RemoveAt(0)
- Removes by index
- nums.Contains(5)
- Checks existence
- nums.Count
- Item count