Editing an array of numbers which length is variable

For the needs of a line drawing program, I need to edit an array of integers. The only constraint on the array is its length, which has to be even, and greater or equal to two. The solution I have for now looks like this:

The [ x ] stands for editable text boxes.

Initially: ( this one represents the default dashed line: - - - -)

[ 1 ] [ 1 ] [ ] [ ]

User has filled one of the two empty fields: (inconsistent state)

[ 1 ] [ 1 ] [ 2 ] [ ]

User has filled the remaining field:

[ 1 ] [ 1 ] [ 2 ] [ 2 ] [ ] [ ]

Is this correct, or is there a better way to do this ?

Edit: I don't want any form of markup language as suggested in one answer.