System.ArgumentOutOfRangeException: 'Index was out of range. copy from one list to another

Question

I built following programm, but I get the out of range error. Basically I would like to copy values from one list to another (from a to b ):

List<int> a = new List<int> { 99, 2, 3, 4, 5, 6 };
List<int> b = new List<int>(6);

for ( int i = 0; i < a.ToArray().Length; i++ )
{
  a[i].ToString().Insert(0, b[i].ToString());
}

for ( int i = 0; i < a.ToArray().Length; i++ )
{
  Console.WriteLine(b[i]);
}

Console.ReadKey();

Answer 1

Just copy the values from the first list to the second list by calling ToList() on the first list:

List<int> uzytkownik = new List<int>() { 99, 2, 3, 4, 5, 6 };

List<int> uzytkownik1 = uzytkownik.ToList();//only values are copied, not the reference to the first list

for (int i = 0; i < uzytkownik1.Count; i++)
{
    Console.WriteLine(uzytkownik1[i]);
}

Console.ReadKey();

If you have to use a for loop then:

List<int> uzytkownik = new List<int>() { 99, 2, 3, 4, 5, 6 };

List<int> uzytkownik1 = new List<int>();

for (int i = 0; i < uzytkownik.Count; i++)
{
    uzytkownik1.Add(uzytkownik[i]);
}

for (int i = 0; i < uzytkownik1.Count; i++)
{
    Console.WriteLine(uzytkownik1[i]);
}

Console.ReadKey();

Answer 2

Have a look at the Array.CopyTo method.

https://docs.microsoft.com/en-us/dotnet/api/system.array.copyto?view=netframework-4.8

Answer 3

The List<T> already has a method for that kind of work. List<T>.AddRange(IEnumerable<T>)

List<int> a = new List<int> { 99, 2, 3, 4, 5, 6 };
List<int> b = new List<int>(6);

b.AddRange( a );

.net fiddle example