Functions in MATLAB that accept text data can be called in one of two ways: command form or function form. Let me show you each of these forms for a function with which you may be familiar that accepts text data: help. I'll call it in three ways that are equivalent: one in command form and two in function form.
help pi % command form
help('pi') % function form
n = 'pi';
help(n) % also function form
When you call the function in command form you don't need to use parentheses or wrap the text in quotes, but what you pass in will literally be accepted as that text. So if I tried to use command form with the variable n I defined above, it won't work.
help n % This will NOT show the help for the pi function
Rather than using command form to call mkdir, use function form like the third line of the example above.
Oh, you should also look at the fullfile function. It will help you assemble your path string.
