How can I make this loop work?

I want to create a function that can translate text input to morse code. But I am suck in the loop. e.g.

>> morserOutputFile('AB')

c =

     1

c =

     2

morsecode =

.-

Here is the code

function morserOutputFile(text)
Dit = '.';
ssp = ' ';
Dah = '-';

    % Defining Characters & Numbers
    A = strcat(Dit,ssp,Dah);
    B = strcat(Dah,ssp,Dit,ssp,Dit,ssp,Dit);
    C = strcat(Dah,ssp,Dit,ssp,Dah,ssp,Dit);
    D = strcat(Dah,ssp,Dit,ssp,Dit);
    E = strcat(Dit);
    F = strcat(Dit,ssp,Dit,ssp,Dah,ssp,Dit);
    G = strcat(Dah,ssp,Dah,ssp,Dit);
    H = strcat(Dit,ssp,Dit,ssp,Dit,ssp,Dit);
    I = strcat(Dit,ssp,Dit);
    J = strcat(Dit,ssp,Dah,ssp,Dah,ssp,Dah);
    K = strcat(Dah,ssp,Dit,ssp,Dah);
    L = strcat(Dit,ssp,Dah,ssp,Dit,ssp,Dit);
    M = strcat(Dah,ssp,Dah);
    N = strcat(Dah,ssp,Dit);
    O = strcat(Dah,ssp,Dah,ssp,Dah);
    P = strcat(Dit,ssp,Dah,ssp,Dah,ssp,Dit);
    Q = strcat(Dah,ssp,Dah,ssp,Dit,ssp,Dah);
    R = strcat(Dit,ssp,Dah,ssp,Dit);
    S = strcat(Dit,ssp,Dit,ssp,Dit);
    T = strcat(Dah);
    U = strcat(Dit,ssp,Dit,ssp,Dah);
    V = strcat(Dit,ssp,Dit,ssp,Dit,ssp,Dah);
    W = strcat(Dit,ssp,Dah,ssp,Dah);
    X = strcat(Dah,ssp,Dit,ssp,Dit,ssp,Dah);
    Y = strcat(Dah,ssp,Dit,ssp,Dah,ssp,Dah);
    Z = strcat(Dah,ssp,Dah,ssp,Dit,ssp,Dit);
    period = strcat(Dit,ssp,Dah,ssp,Dit,ssp,Dah,ssp,Dit,ssp,Dah);
    comma = strcat(Dah,ssp,Dah,ssp,Dit,ssp,Dit,ssp,Dah,ssp,Dah);
    question = strcat(Dit,ssp,Dit,ssp,Dah,ssp,Dah,ssp,Dit,ssp,Dit);
    slash_ = strcat(Dah,ssp,Dit,ssp,Dit,ssp,Dah,ssp,Dit);
    n1 = strcat(Dit,ssp,Dah,ssp,Dah,ssp,Dah,ssp,Dah);
    n2 = strcat(Dit,ssp,Dit,ssp,Dah,ssp,Dah,ssp,Dah);
    n3 = strcat(Dit,ssp,Dit,ssp,Dit,ssp,Dah,ssp,Dah);
    n4 = strcat(Dit,ssp,Dit,ssp,Dit,ssp,Dit,ssp,Dah);
    n5 = strcat(Dit,ssp,Dit,ssp,Dit,ssp,Dit,ssp,Dit);
    n6 = strcat(Dah,ssp,Dit,ssp,Dit,ssp,Dit,ssp,Dit);
    n7 = strcat(Dah,ssp,Dah,ssp,Dit,ssp,Dit,ssp,Dit);
    n8 = strcat(Dah,ssp,Dah,ssp,Dah,ssp,Dit,ssp,Dit);
    n9 = strcat(Dah,ssp,Dah,ssp,Dah,ssp,Dah,ssp,Dit);
    n0 = strcat(Dah,ssp,Dah,ssp,Dah,ssp,Dah,ssp,Dah);

    text = upper(text);
    vars ={'period','comma','question','slash_'};
    morsecode='';
    a = length(text);
    i = length(text);
    while a > 0
    c=(i-a)+1
    switch c
        case text(c)=='A'
            morsecode = strcat(morsecode,A);
        case text(c)=='B'
            morsecode = strcat(morsecode,B);
        case text(c)=='C'
            morsecode = strcat(morsecode,C);
        case text(c)=='D'
            morsecode = strcat(morsecode,D);
        case text(c)=='E'
            morsecode = strcat(morsecode,E);
        case text(c)=='F'
            morsecode = strcat(morsecode,F); 
    end
    a = a-1;
    end
    display(morsecode);

Answer 1

[Walter Roberson]

Use an ascending for loop instead of a descending while loop.

Your code could be much more efficient if you used a cell array.

targets = ['A' : 'Z', '.,?/', '0' : '9'];
morse_translations = {A, B, C, D, .... };

[tf, idx] = ismember(text(c), targets);
if tf
   this_code = morse_translations{idx};
   ...
end

[KAI YIN CHAN]

Thank you so much! Especially for showing how I can make it more efficient.