Why this code is doesnt pass though it gives me proper ans in matlab
in = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890;,.!& '
out = 'NOPQRSTUVWXYZABCDEFGHIJKLMnopqrstuvwxyzabcdefghijklm1234567890;,.!& '
s2 = s1
for i=1:length(s1)
x= find(in == s1(i)) ;
s2(i) = out(x)
end

specialcase = find(s2 == '&')

if ~isempty(specialcase)
s2(specialcase)='
s2(specialcase+1:specialcase+3)=[]
end

Nice problem. Also like the encoder and decoder are the same (ROT13 applied twice gives back the original text).

A small solution that doesn't use "regexp"!

Sorry, mistake in crediting comment in code; this solution is based on Jan's solution (Solution 17079) -- not Jan Orwat's solution.

A modification of Solution 819585.

Not my best work :/

It's still interesting to see other logical approaches like this, though.
One thing that can be done is to remove the inner "if" statements, as illustrated in Solution 1275889. https://www.mathworks.com/matlabcentral/cody/problems/78-implement-a-rot13-cipher/solutions/1275889

How does this work?

It is an old trick. You can pass any group of commands wrapped in a regexp command as one string. It used to be fun and can be used virtually for any problem, but I no longer use it since it is against the purpose of Cody.