Trying to make a function for Caesar Encryption -- need help.

I've got a project which involves designing a GUI that can encrypt a string using Caesar encryption. I've been making this function file to use in the GUI .m file, but I've encountered some problems. I think I've got the method properly, I just can't seem to get it right without any errors.

function output = encCsar(word,key)

numWord = uint8(word);
numKey = uint8(lower(key)) - 96;

for i = 1:numel(numWord)
if ( numWord>=65 & numWord<=90 )
    numWord=mod(numWord-65+numKey,26);
    output(i,1)=char(numWord+65);
    elseif ( numWord>=97 & numWord<=122 )
    numWord=mod(numWord-97+numKey,26);
    output(i,1)=char(numWord+97);
    else
    error('Please enter a string and a number key.')
end
end

My method is:

1. Convert "word" (a string) into its respective numerical array in ASCII.
2. Convert the key (one lowercase letter to determine how much to shift by) to its respective ASCII number.
3. run a for loop that runs for each element of the numerical array numWord
4. Apply the Caesar encryption formula (num value of the letter + num value of the key) in mod 26, and I had it run for both uppercase and lowercase letters just in case the string isn't completely lowercase or uppercase.
5. It then outputs each encrypted element as a new array, and it converts it back to characters.

That's what it's supposed to do in theory, but I've gotten the error I set up ('Please enter a string and a number key.') in case it fails each time. If I try commenting out the else part, the function just doesn't do anything. How should I go about fixing this? Any answers or help would be appreciated.

Answer 1

[Jan]

I assume, that word is a string or char vector. Then

numWord = uint8(word);

converts it to a vector of type uint8. Now

for i = 1:numel(numWord) 

starts a loop over all elements of this vector. But

    if ( numWord>=65 & numWord<=90 )

uses the complete vector in the condition. If Matlab's if gets an array as condition, if performs this implicitly:

if all(X(:)) && ~isempty(X)

Most likely you want to use the loop index i:

    if numWord(i) >= 65 & numWord(i) <= 90
    %         ^^^                ^^^    

By the way, it is easier to operate on the characters directly:

for i = 1:numel(word)
   if word(i) >= 'a' && word(i) < 'z'
       output(i) = char(65 + mod(word(i) - 65 + numKey, 26));
   ...

Answer 2

[Juan Sebastián Hincapié Montes]

I've got a solution to this problems... hope this help you!

function [coded] = caesar(v ,sa)
secret = double(v);
code = ones(1, length(v));
for ii=1:length(secret)
    if secret(ii)+sa > 126      %greater than 126
        remainder=rem(sa,95);
        if remainder + secret(ii)>126  %if the double plus the remainder is greater than 32
            code(ii)=31+(remainder-(126-secret(ii)));
        else
            code(ii)=remainder+secret(ii); %if the double plus the remainder isn't greater than 32
        end
        
    elseif secret(ii)+sa < 32  %lower than 32
        remainder=abs(rem(sa,95));
        if secret(ii)-remainder < 32  %if the double plus the remainder is lower than 32
            code(ii)=127-(remainder-(secret(ii)-32));
        else
            code(ii)=secret(ii)-remainder; %if the double plus the remainder isn't lower than 32 
        end
    else
        code(ii) = sa + secret(ii); %everything is normal
    end
end
coded=char(code);
end

[MANIKANTA THOTA]

can you tell me why you took 95 in the reminder