How do I "backward" a string in matlab: turn "a" into "z", "b" into "y", "c" into "x", etc.

I used the following code, but got an error...

function output_string = codeit(txt);

for ii = 1:length(txt)
    input_char = txt(ii);
    if input_char>='a'&&input_char<='z';
        reverse_alphabet= ['z' 'y' 'x' 'w' 'v' 'u' 't' 's' 'r' 'q' 'p' 'o' 'n' 'm' 'l' 'k' 'j' 'i' 'h' 'g' 'f' 'e' 'd' 'c' 'b' 'a'];
        reverse_alphabet_index = input_char - 'a' + 1;
        output_char = reverse_alphabet(reverse_alphabet_index);
        output_string(ii) = output_char;
    elseif input_char>='A'&&input_char<='Z';
        reverse_alphabet= ['Z' 'Y' 'X' 'W' 'V' 'U' 'T' 'S' 'R' 'Q' 'P' 'O' 'N' 'M' 'L' 'K' 'J' 'I' 'H' 'G' 'F' 'E' 'D' 'C' 'B' 'A'];
        reverse_alphabet_index = input_char - 'A' + 1;
        output_char = reverse_alphabet(reverse_alphabet_index);
        output_string(ii) = output_char;
    end
end
end

ans =
Feedback: Your function performed correctly for argument(s) 'azAZ'
    Feedback: Your program made an error for argument(s) '`_^]\[ {|}~'

      Your solution is _not_ correct.

[Guillaume]

Note that

reverse_alphabet= ['z' 'y' 'x' 'w' 'v' 'u' 't' 's' 'r' 'q' 'p' 'o' 'n' ...

is exactly the same as

reverse_alphabet= 'zyxwvutsrqpon...'

The latter of course being much easier to type. Probably even better would be:

reverse_alphabet= 'z':-1:'a'; %or fliplr('a':'z')

[Stephen23]

@Darshan Kanungo: What is the specified/expected output for the input string '`_^]\[ {|}~' ? This is currently not specified in the question or the error message, so we have no idea how the function should behave with non-alphabetic characters. You need to specify this for us!

[Darshan Kanungo]

Write a function called codeit that takes a string txt as input and returns another string coded as output. The function reverses the alphabet: It replaces each 'a' with 'z', each 'b' with 'y', each 'c' with 'x', etc. The function must work for uppercase letters the same way, but it must not change any other characters. Note that if you call the function twice like this str = codeit(codeit(txt)) then str and txt will be identical.

Answer 1

[Stephen23]

You could use char:

>> char(219-'abc')
ans =
zyx

Note this assumes that the text consists only of lower-case alphabetic characters. If you want mixed case then this will be much more complicated.

EDIT in response to the OP completely rewriting their question, removing the original example and stating new requirements.

The new code given in the question is very complicated: solving this in a loop is slow and a waste of MATLAB's code vectorization abilities. Here is a completely vectorized function based on isstrprop that reverses only the alphabetic characters (keeping case the same) and ignores all other characters:

function str = str_rev(str)
idx = isstrprop(str,'upper');
str(idx) = char(155-str(idx));
idx = isstrprop(str,'lower');
str(idx) = char(219-str(idx));
end

And some examples showing it in action:

>> str_rev('abc')
ans =
zyx
>> str_rev('AbcD')
ans =
ZyxW
>> str_rev('Hello World!')
ans =
Svool Dliow!

[Darshan Kanungo]

when i used a mixed case

[Darshan Kanungo]

thanku sir....

Answer 2

[Jan]

function out = codeit(in)
lut = char(1:255);
lut(['a':'z', 'A':'Z']) = ['z':-1:'a', 'Z':-1:'A'];
out = lut(in);

Answer 3

[charu sharma]

For a simple understanding you can follow this too: http://farzicoders.blogspot.in/2015/08/write-function-called-codeit-that-takes.html

[Guillaume]

I wouldn't classify this answer as spam, the link is relevant to the question (as long as it does not disappear).

However, the answer posted in the link is a poor example of coding (unnecessary loops, unnecessary conversions, unnecessary use of temporary variables), so is of little value.