Hi Jim,
Remember that cell arrays can hold arbitrary data (including other cell arrays) and that while [] is concatenate, {} is "build a cell array". From the documentation about {}:
"Braces are used to form cell arrays. They are similar to brackets [ ] except that nesting levels are preserved."
Therefore, after your fourth assignment to legends, you actually have a cell array containing two elements, a cell array and a string.
Instead, consider using:
>> legends = {'first'}
legends =
'first'
>> legends(end+1) = {'second'}
legends =
'first' 'second'
>> legends(end+1) = {'third'}
legends =
'first' 'second' 'third'
Even better yet, if you know all the strings ahead of time, generate it all at once such as:
legends = {'first' ...
'second' ...
'third'}
legends =
'first' 'second' 'third'
todd