MATLAB: How could I fix the script

algorithm

If I am using the function rotatedText=rot(text,n). First things for say, I have to make sure that my script should apply a Caesar cipher encryption with a shift to n to input string text. The function should shift uppercase letters to uppercase letters and lowercase letters to lowercase letters. If the string text contains numbers or special characters it should leave them the same. The function should work for negative shifts and shifts greater than 26 or less than -26.
function rotatedText=rot(text,n);
  n=mod(n,26)
    for i=1:length(text)
        ascii=double(txt(i));
        if ascii>=65 && ascii<90
            rotatedText(i)=char(ascii+n);
        elseif ascii>=97 && ascii<=122
            rotatedText(i)=char(ascii+n)
        else ascii>=33 && ascil<=65 || ascii>=90 && ascii<97 || ascii>=122 && 
            ascii<=126;
            rotatedText(i)=char(ascii);
        end
  end

Best Answer

Decide which range you are in. If it is one of the two ranges to be affected, record the character that is the beginning of the range and calculate the distance of the character from the beginning of the range. Add the shift to the distance. Take mod 26. Add the recorded beginning of the range, and convert to char and save. Otherwise save unchanged. Repeat for all characters.
... You can vectorize this in at most two cases.
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