List<long> testList = new List<long>(id) gives error in C#

Question

long id= 10;
List<long> testList = new List<long>(id);   /*creating to List of long */

Above statement gives error in C# and intelligence saying to convert it to int. At the same time when i do it like below it is working as expected.

long id= 10;
List<long> testList = new List<long>();    /*creating to List of long */
testList.Add(id);

what is the reason behind it?

Answer 1

List initialization (probably want you want to do) is done like this in C#:

long id = 10;
List<long> testList = new List<long>() { id };

Inside the curly brackets you can put multiple elements separated by comma which the list shall initially contain.

Answer 2

There are 3 constructors for the List class.

public List()
public List(IEnumerable<T> collection)
public List(int capacity)

You are trying to initialize the list using the constructor that takes capacity (which should be int, not long).

List.Add() method adds data to the list. So, your statement of creating list object v/s adding element to list is what giving you the error.