How can I store and access strings in a cell array?

I'm writing a program that requires dynamic storage and retrieval of strings. The logic flow looks something like this code:

initial_string = 'ABCDEF';
old_string = initial_string;
initial_pos = 1;
current_pos = 1;
previous_val = 1000;
best_string = cell(length(initial_string));

while current_pos < length(initial_string)
   new_string = generate_new_string % generates new string of same length as
   %initial string
   [test_val, increment] = get_val(new_string, old_string);

     if test_val < previous_val 
        best_string(current_pos) = new_string;
        previous_val = test_val;
     end

     if increment == true
        old_string = best_string{current_pos};
        current_pos = current_pos + 1;
     end
end

The problem is that get_val produces an error after increment becomes true because old string, rather being a string, is read as '[]'. How do I get old_string to become the string stored at best_string(current_pos) instead of the cell?

[Azzi Abdelmalek]

what is generate_new_string ?

[Jan]

initial_string = 'ABCDEF';
best_string = cell(length(initial_string))

This creates a {6 x 6} cell. Is this wanted?

I do not understand the question. Which error does get_val produce? Perhaps you want:

best_string{current_pos} = new_string;   % Curly braces