I need to add '0' to the end of plaintext, then I can use it within cipher to deduct it equally to 64-bit, the error in below code (append)

plaintext = 'In literature, cryptosystems based on digital chaos were mostly designed for a broad range ' 
plainlen = length(plaintext);
y = mod(plainlen,8);
if y ~= 0 
    x = 8-y;
    for j=1:x
        plaintext=append(plaintext,'0');     % 
    end    
end

[Voss]

What's the problem?

[Hussain]

The problem was that the in (append) It's wroks normally when I use it in Matlab ver. 2021a, but it doesn't work and give error in Matlab ver. 2013b.

but I solved it,

Thanks and appreciate your response.

[Walter Roberson]

append came into existence at the same time as string objects came into existence, which was a few years after R2013b.

Answer 1

[Walter Roberson]

plaintext = 'In literature, cryptosystems based on digital chaos were mostly designed for a broad range ' 
plainlen = length(plaintext);
y = mod(plainlen,8);
if y ~= 0 
    plaintext = [plaintext, repmat('0', 1, 8-y)];
end