How create 2 arrays from a multiline textbox for each row in C#? Then I need to plot in a graph those arrays

string[]str = textBox3.Text.Split(',');

foreach (string row in str)
        {
           
            textBox2.Text = str[0];
        }

try this, it was tested in visual studio:

var s =
@"14:33:29, 831

  14:33:30, 834

  14:35:1, 830

  14:35:2, 833";
  
var strArr = s.Replace(" ", "").Replace("\n", ";")
.Split(";",StringSplitOptions.RemoveEmptyEntries).Where(a => a.Length>3).ToArray();

    var len=strArr.Length;
    var arr1= new string[len] ;
    var arr2 = new string[len];

    for (var i = 0; i < len; i++)
    {
        var arr = strArr[i].Trim().Split(",");
        if (arr.Length == 2)
        {
            arr1[i] = arr[0];
            arr2[i] = arr[1];
        }
    }

result

arr1= {"14:33:29","14:33:30","14:35:1","14:35:2"};
arr2 ={"831","834","830","833"};