在MATLAB中使用迭代解码消息

Question

So I am kind-of stuck on this problem for homework. Though that's nothing new, I felt fine using just loops, but adding iteration into the mix is throwing me off. Anyway, what I would like help with is decoding a message in MATLAB. There are two different types of messages: one that involves a bunch of characters, and one that involves spaces(so an actual sentence). If I have a string of characters, I have to find every nth character, if it's a string of characters, I have to find every nth character.

function[code]= decodeStr(str, index)
    code = [];  %// Starts me off with an empty vector to populate
    word_in_message = strsplit(str, ' ');  %// Splits up my vector
    word_in_message = char(word_in_message); %//Turns it into a character, which I need
    find_spaces = find(str == ' '); %// Finds spaces, how I know it's not a character string
    words = (find_spaces + 1); %//Index es the word, but not too sure I need this
    Counter = 1; %// I plan to use this in the character string

    while index <= length(str)
        if find_spaces > 0 %// If it is a string with words, they'll be spaces
            code = word_in_message(index, :); %// This works in the command window. 
            code = [str(index)];
        end
        index = index + 1 ;
    end

end

As you can see, I am sadly lost. I know I can use words_in_message(index, :) in the command window to get the full word, but it errors out in the function. It'll complain about exceeding the dimensions and while I can see why that happens (the index = index + 1 being the culprit), I am unsure of what to do to fix it. I just keep getting it to feed back the whole string to me, which is not what I wanted. Any suggestions?

TestCases
 str = ['I want to go  to the   track meet and eat a Jimmy Johns ''gourmet sandwich ...
 on the first with    Wednesday Adams.'];
 [out1] = decodeStr(str,4)
      => out1 = 'go meet Jimmy on Wednesday'
[out2] = decodeStr('www.harttoregerill.com/op',3)
          => out2 = 'waterloo'

Sorry if this seems a bit vague. My carpal tunnel is flaring up, so I'm trying to avoid typing a lot :/

Answer 1

function code = decodeStr(str, index)
    if find(str == ' ', 1)
        words = strsplit(str, ' '); 
        code = strjoin(words(index : index : end));
    else
        code = str(index : index : end);
    end;
end

Answer 2

I don't have enough rep to comment it so: @Cheery

line 4: code = strjoin(words(index : index : end));

Edit : the default delimiter of function strjoin is space, no need to specify it