Simple Encryption Code check

I have written a code to solve this problem:

Caesar's cypher is the simplest encryption algorithm. It adds a fixed value to the ASCII (unicode) value of each character of a text. In other words, it shifts the characters. Decrypting a text is simply shifting it back by the same amount, that is, it substract the same value from the characters. Write a function called caesar that accepts two arguments: the first is the character vector to be encrypted, while the second is the shift amount. The function returns the output argument coded, the encrypted text. The function needs to work with all the visible ASCII characters from space to ~. The ASCII codes of these are 32 through 126. If the shifted code goes outside of this range, it should wrap around. For example, if we shift ~ by 1, the result should be space. If we shift space by -1, the result should be ~.

This is what I have so far, it almost works. When i put in "coded = caesar('ABCD', 3)" as the input, the output is "G" instead of "DEFG" and when the input goes outside the range, the output is just " ". Any help with what I am getting wrong would be appreciated

function [coded] = caesar(vector, shift)

i = double(vector);

x = i;

for j = 1:length(i);

if i(j) + shift > 126;

x = 126 + shift - 95;

elseif i(j) + shift < 32;

x = 32 + shift + 95;

else

x = i(j)+shift;

end

coded = char(x);

end

[Walter Roberson]

What does your code do if the user requests a shift of 1000?

Answer 1

[Les Beckham]

You are only saving one element of x. You need to index x like you did i.

So:

function [coded] = caesar(vector, shift)
i = double(vector);
x = i;
for j = 1:length(i)
    if i(j) + shift > 126
        x(j) = 126 + shift - 95;
    elseif i(j) + shift < 32
        x(j) = 32 + shift + 95;
    else 
        x(j) = i(j)+shift;
    end 
    coded = char(x);
end

Result;

>> caesar('ABCD',  3)

ans =

    'DEFG'

>> 

[Bil Ly]

Thanks, that makes sense. any idea why the function is outputting a blank space when i try to go above or below 32 or 126 on the table?

[Les Beckham]

32 is the ASCII code for a space. 127 is the ASCII code for DEL which is an "unprintable" character. Some of the ASCII codes correspond to actions that teletypes or other "old fashioned" devices were to take when they received those characters.

The typical printable English letters, numbers, and punctuation marks lie between 32 and 126. You can search "ASCII table" or look at the Wikipedia article on ASCII to learn more: ASCII

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