convert string array into int list

// using Linq; // required

string[] strTabTypes = tabtype.Split(',');

List<int> lstInt = strTabTypes.Select(str => Convert.ToInt32(str)).ToList();

Note that this approach is going to throw a System.FormatException error if any of the strings in the 'strTabTypes array are not valid for conversion to Int32.

Here's one way you could approach error-checking in the conversion using Linq:

Int32 testInt;

List<int> lstIn2 = strTabTypes
    .Select(str => Int32.TryParse(str, out testInt) ? testInt : Int32.MaxValue)
    .ToList();

In this example, if there is any string that can't be converted to Int32, then Int32.MaxValue is returned: 2,147,483,647 : hexadecimal 0x7FFFFFFF.

But, perhaps the right thing for you to do is put the conversion in a Try/Catch block and handle the error, or re-throw the error ?

The code below provides for a more robust solution compared to your original solution.

string tabtype = "1,5,11"; // Just an example

// This way you make sure that there are no empty positions in the string array
string[] strTabTypes = tabtype.Split(new char[] { ',' },
                                      StringSplitOptions.RemoveEmptyEntries);
List<int> lstInt = new List<int>();

foreach (string s in strTabTypes)           // foreach is easier to use in this case
    lstInt.Add(Convert.ToInt32(s.Trim()));  // Removes head and tail spaces

You can of course add an error check according to solution 1.