I worked on a code for caesar cypher problem it should work correctly but it does not

The function gives wrong outputs in some test cases.

function coded=new_caesar(ch_v,shift);
x=double(ch_v); 
for jj=1:length(x)
    if (x(jj)>=48) && (x(jj)<=57)
        y=char(x(jj));
        z=str2num(y);
        x(jj)=z+shift;
    else
        x(jj)=x(jj)+shift;
    end
end
for ii=1:length(x)
    if (x(ii)>=0) && (x(ii)<=9)
        x(ii)=num2str(x(ii));
    elseif x(ii)<32
        x(ii)=char(126);
    elseif x(ii)>126
        x(ii)=char(32);
    end
end
coded=char(x);

Answer 1

[Tejas]

Hello Amany,

The reason the above code produces incorrect results on certain test cases is due to the lack of wrap-around when a character's ASCII value is shifted by an integer. Here is a simple example for better understanding:

• The digit '0' has an ASCII value of 48. When shifted by 3 positions, it becomes ASCII 51, representing digit '3', which works as expected.
• However, when the digit '8', with an ASCII value of 56, is shifted by 3 positions, it becomes ASCII 59, which does not correspond to the digit '1'. Instead, the ASCII value should wrap-around to 49, representing digit '1'.

The wrap-around can be achieved using the 'mod' function. Refer to this documentation for more information on it:

https://www.mathworks.com/help/releases/R2023a/matlab/ref/mod.html

Here are some example code snippets to wrap-around ASCII values:

• For digits 0 to 9:

    if (x(jj) >= 48) && (x(jj) <= 57)  
        x(jj) = mod(x(jj) - 48 + shift, 10) + 48; 
    end 

• For lowercase alphabets a to z:

    if (x(jj) >= 97) && (x(jj) <= 122)  
        x(jj) = mod(x(jj) - 97 + shift, 26) + 97;  
    end