You don't actually have to convert the logical value into double and compare it to 1. From the documentation for the if keyword: "if expression, statements, end evaluates an expression, and executes a group of statements when the expression is true." The only problems I see with your code is that you're not using parentheses to call fprintf and that you didn't end the if block with an end statement (though that latter problem could be that you just didn't copy and paste it from your code.)
x = [];
if isempty(x)
fprintf('The x array is empty');
else
fprintf('The x array is not empty');
end
