caesar cyphor encryption 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 ~.

for the first part of the code...this works

function coded=caesar(A,n)
char_set=char(32):char(126)
    coded=char(A+n);
end

But if i want to maintain the range between 32 and 126 ....and also wrap around the same values as asked in later half of question , it doesnt work

function coded=caesar(A,n)
char_set=char(32):char(126)
while A <=char_set
    coded=char(A+n);
end
end

please help me with the concerned code buiding ....( expect a simple approach , since iam a begineer)

test for these outputs

caesar('ABCD',1)
ans =
    'BCDE'
caesar('xyz ~',1)
ans =
    'yz{! '
caesar('xyz ~',-1)
ans =
    'wxy~}'    %these are correct answers to the code 

[Mounic Kumar]

we will even get by using loops, but it is quite messy and challenging

function coded= caesar(A,n)
k=length(A);
b=double(A);
c(1,k)=0;
for i=1:k
    
    if b(1,i)+n >126
        m=126-b(1,i);
        exc=n-m;
        while exc>95
            exc=exc-95;
        end
        c(1,i)=31+exc;
    elseif b(1,i)+n<32
        d=b(1,i)-32;
        less=n+d;
        while less<-95
            less=less+95;
        end
        c(1,i)=127+less;
    else
        c(1,i)=b(1,i)+n;
    end
end
coded=char(c);

try it, you will get output.....

[Guillaume]

but it is quite messy and challenging

As I explained in my answer, it's trivially done using mod or rem. You only need 1 line of code, and not a very long line at that. (a subtraction by an integer, a mod, an addition by the same integer).

[Mounic Kumar]

I tried your 1 line of code idea, but I didn't get the correct result. So, why don't you explain a little longer...?

[Guillaume]

Look at the examples in my answer. And above I've given you the exact steps required

As I said I don't give solution to homework problems as figuring out the solution is the whole point of the homework.

>> caesar = @(message, shift) xxxx(xxx(message x shift x yy, zz) x yy)
caesar =
  function_handle with value:
    @(message,shift)xxxx(xxx(messagexshiftxyy,zz)xyy)
>> caesar('~', 1)
ans =
    ' '
>> caesar(' ', -1)
ans =
    '~'
>> caesar('The quick brown fox + 12345', 2)
ans =
    'Ymj%vznhp%gwt|s%kt}%0%6789:'

I've masked the actual functions and numbers used, but as you can see a one line of code is all that is needed.

[Guillaume]

As I've explained above and below, the whole thing can be done in just one line with mod or rem , with no loop needed. You could indeed try to implement mod or rem yourself as you've tried to do but why bother?

Your code is wrong. In most cases you forget to add n. Some cases are also covered by other more generic ones.

[sadek kouz]

this is how I solved it

function coded    = caesar(lettre,  n)
N = n - 95 * fix(n/95);

a=double(lettre+N);
for i=1:length(a);
if a(i)>126
    a(i)=a(i)-126+31;
elseif a(i)<32
    a(i)=a(i)+126-31;
end

end
coded=char(a);

end

[Aravind Meyappan]

HI Sadek

I had the exact same solution except for the 2nd line , where N is assigned a value, and i am getting error in my code for certain values. whats the significance of the 2nd line code?

thanks in advance

[Walter Roberson]

That second line does the same computation that would be done for

N = mod(N, 95);

[Aravind Meyappan]

but why is that necessary? the mod function?

can't we just add the input number "n" to the input string directly?

[Walter Roberson]

What happens if the user enters n = 1234 ?

If you look through the various implementations people have posted here, you will see that some of them use a loop to keep subtracting or adding until the value is within range. The particular code you are looking at now instead uses a calculation equivalent to mod() to get the value into a range such that only a single addition or subtraction is needed to get back into range (provided, that is, that the input was ASCII and not, for example, 'ŭ' (character 365)

[Saisunder Chaganty]

function y = caesar2(ch, key)
 v = ' ' : '~'; 
[~, loc] = ismember(ch, v);
 v2 = circshift(v, -key);
 y = v2(loc);
 end

[Walter Roberson]

Interesting. But what should happen if one of the original characters was not in the range space to ~ ? For example newline characters are not in that range.

[vamsi]

I tried this way.

function coded = caesar(cv, sh)
cv=cv+mod(sh, 95);
coded=char(cv-(cv>126).*95+(cv<32).*95);
end

[SONU NIGAM]

function coded = caesar(char_vec,shift_amount)
char_value = char_vec+shift_amount;
for ii = 1:length(char_value)
    if char_value>126
        coded = char(char_value-95);
    elseif char_value<32
        coded = char(char_value+95);
    else
        coded = char(char_value);
    end
end
end

I got correct output but in the assignment when i run this program it shows error...What fault i did i m unable to notice,if anyone can explain me then plz help me.

[Danial Ahmad]

the problem is that e.g if the value of char_vec is 120 i.e x and the shift_amount is let's say 100 then char_value will be 220 and when you subtract 95 form that you dont get the desired result

[Rik]

@Danial, which code are you talking about? Sonu already mentioned their code doesn't work.

Answer 1

[Yitong Liu]

function coded = caesar(M, n)
num = double(M);                        %Converts string into double
num2 = num;
N = n - 95 * fix(n/95);
for i = 1:length(num);  
    if  num(i) + N < 32                 %If ASCII value goes below 32
        num2(i) = 126 - (31- num(i) - N);
    elseif num(i) + N > 126             %If ASCII value goes beyond 126
        num2(i) = 32 + (num(i) + N -127);
    else 
        num2(i) = num(i) + N ;          %If ASCII value goes normal
    end
coded = char(num2);
end

I spent halfhour on solving this problem, a little bit hard.

This is correct code. Hope it helps.

[Yitong Liu]

function txt = caesar(txt,key)
    txt = double(txt) + key;
    first = double(' ');
    last = double('~');
    % use mod to shift the characters - notice the + 1
    % this is a common error and results in shifts 
    % being off by 1
    txt = char(mod(txt - first,last - first + 1) + first);
end

This is offcial solution 1 - uses the mod function

[Yitong Liu]

function y = caesar2(ch, key)
    v = ' ' : '~';
    [~, loc] = ismember(ch, v);
    v2 = circshift(v, -key);
    y = v2(loc);
end

This is offcial solution 2 - uses the circshift function

As I am a new learner, both of them are easier than mine.

Anyway, Hope them do you guy a favor.

Happy to discuess about new solutions to this problem!

[Debaparna Goswami]

function coded = caesar(vector,shift)

message = double(vector)+ shift
l = length(message);
for i = 1:l
    if message(i)>126
        while message(i)>126
         message(i) = 31+(message(i)-126)
        end
    end
    if message(i)<32
        while message(i)<32
         message(i) = 126-(31-message(i))
        end
    end
end
coded = char(message);

I hope this will work too.

[Raj Tilak]

can you please explain me why you have taken this

N = n - 95 * fix(n/95);

and also

num2(i) = 126 - (31- num(i) - N); %in here i took 32 instead of 31 and
num2(i) = 32 + (num(i) + N -127); %31 for 32 and 126 instead of 127 ..my code didn't work

can you explain why??

[Walter Roberson]

n - 95 * fix(n/95) is calculating the equivalent of mod(n,95) -- the remainder left over after dividing into chunks of 95.

[Walter Roberson]

num2(i) = 126 - (31- num(i) - N); %in here i took 32 instead of 31 and

That code is within num(i) + N < 32 test. Let's say num(i) is 38 and N is -9 so num(i)+N = 29, and 29 < 32 so the test works. The distance 29 would have to advance to reach 32 is 3, and 32 - (num(i)+N) = 3, The maximum value is 126, so a value that was one back from what it should be should map to 126, and a value that was 2 back from what it should be would map to 125, and a value that was 3 back from what it should be would map to 124. Flipping that around, if you advance 3 forward from 124 you get 127 -- so we can work with the expression 127 - (32 - (num(i)+N)) . Now if you subtract 1 off of those first two numbers, you get the same equation: 127 - (32 - (num(i)+N)) is the same as 126 - (31 - (num(i)+N)) which is the same as 126 - (31 - num(i) - N)

The equation might have been more clearly written as 127 - (32 - (num(i)+N)) but mathematically 126 - (31 - num(i) - N) is equivalent.

[Tim Hauser]

-3 - 95 * fix(-3/95) does not result in the same as mod(-3,95) so are they really equivalent?

[Tim Hauser]

never mind, -3 and 92 are the same shift after all.

[Walter Roberson]

You are correct, though, that fix() has different behaviour for negatives.

[Mohammed Shahin P]

Your code was of great help. Thankyou

[Mahendran P]

why do we do that fix() step. i did the same code without using that step and i got it wrong

[Walter Roberson]

Suppose n is 103. Then

103 - 95 * (103/95)

gives exactly 0.

103 - 95 * fix(103/95)

gives 8, which tells you that 103 is 8 more than a multiple of 95.

mod(103,95)

also gives 8.

Another way of writing the sequence would be

while n >= 95
    n = n - 95;
end
while n < 0
    n = n + 95;
end

[Kilaru Venkata Krishna]

Thanks for this explanation

[Amith Anoop Kumar]

Here what is the speciality of 95 , why are we taking mod with 95

[Walter Roberson]

char(32) to char(126) is a range of 126-32+1 = 95 possibilities

[Amith Anoop Kumar]

Ok thanks

[Iulian Danciu]

@Debaparna Goswami Why did you use while loop? I tried in the same way, but without using while loop? Can you please explain me the reason using while? thank you!

[Abdulhameed Araromi]

Please, the third line of the code N = n..., Please why is it necessary we write that? Please kindly explain

[Walter Roberson]

I already explained why N is set to that value, https://www.mathworks.com/matlabcentral/answers/466636-caesar-cyphor-encryption-problem#comment_832722

You will need to "Show older comments"

[Noor Ul Zain]

Walter sir can you please explain the code that uses mod function. why in the last we add first and not first -1.

Kindly explain. I am unable to understand with mod function

[Dhinesh Kumar]

Super bro

[THIERNO AMADOU MOUCTAR BALDE]

Thanks sir, could you please give more details about the use of N and this value of '95'

[Rik]

You can reconstruct it from the other two magic numbers in the code: it is the number of values in the range 32:126.

[Panagiotis Papias]

Yitong Liu

I am sorry to bother you, could you please explain why it is necessary:

N = n - 95 * fix(n/95)?

best regards,

[Walter Roberson]

@Panagiotis Papias

That has already been explained several times, starting at https://www.mathworks.com/matlabcentral/answers/466636-caesar-cyphor-encryption-problem#comment_832722

You may need to "Show 22 older comments" to read the discussion.

[Sai Krishna Praneeth Duggirala]

I'm sorry sir , but it isn't explained why it is done rather it is explained what has it done

[Rik]

@Sai Krishna Praneeth Duggirala Try it without it. Do you notice something? Can you think what kind of values can be stored in double and char?

[Kartik rao]

con someone explain what mod function does here?

[SOUMYAJIT MONDAL]

mod function finds the remainder

[Walter Roberson]

@Kartik rao

char(32) to char(126) is a range of 126-32+1 = 95 possibilities. If you were shifting forward, if the original value were large enough, and the shift were large enough, then the total could be greater than 126. For example,

'z' + 23

ans = 145

When that happens, as you count forward from your original letter, when you get to 126, the next value after that should not be 127 but instead should be 32, and you would continue counting from that.

But the shift that the user can request is not restricted; the user could request, for example, a shift of 1000. You would have to have counted through 126, 32, 33, ... 126, 32, 33, ... 126, 32, 33.. several times.

Now, you could write a loop,

while shift_count > 0
  current_characters = current_characters + 1;
  shift_count = shift_count - 1;
  current_characters(current_characters == 127) = 32;
end

but this is not efficient. You could be more efficient by first writing

while shift_count > 95
   shift_count = shift_count - 95;
end

A shift count of (say) 200 is equivalent to a shift count of 95 followed by a shift count of 95 followed by a shift count of 10, But a shift count of 95 leaves everything where it was, so that shift count of 200 is equivalent to a shift count of 10: every group of 95 in the shift "wraps back" to the beginning.

But using a loop to make this reduction of the shift count is not as efficient as it should be. Instead you should be able to calculate how many would be left over after you removed all full multiples of 95. And that is a calculation that mod() makes: mod(shift_count, 95) asks "how many is left over after you remove full multiples of 95?": that is what the mod() function is designed for, to calculate remainders after removing integer multiples of a number.

So: mod() is used to remove the effect of "wrapping" past the end of the char(126) end. And it turns out that you can use it to calculate the end-point:

Subtract off the base of 32. Calculate mod(characters_minus_32 + shift_count, 95) . Add back 32, and you have the result you need.

Answer 2

[Marilou]

function coded= caesar(string,shift)
value=string+shift;

for i=1:length(value)
    while value(i)<32
        value(i)=value(i)+95;
    end
    while value(i)>126 
        value(i)=value(i)-95;
    end

end
coded=char(value);

[Arpit Srivastav]

Bro If this works I gotta say, You did it beautifully!

[Kim Ngo]

I did something similar to this and it worked; I just used sprintf to concatenate individual chars inside the for loop

[Toufik Zisan]

This is just the perfect code. Excellent job dear.

[Raghav Jha]

thank you bro , i struggled for this problem and i tried many different method but none of them suceeded.

[Abhishek Choudhury]

beautiful

[Travis Ha]

I have a question. I did value (1:length(value)) in everything instead of i and didn't use the for loop. This ended up not working because for some reason the function completely skipped over the while loop with value(i)>126. Can someone please explain to me why it did this?

[Walter Roberson]

Travis Ha:

In MATLAB, when you use if or while then the body of the statement is done only if all the items being tested are non-zero. For example,

if [1 5] > 3

the [1 5] > 3 becomes [false true] and when that is tested, the first element is zero (false is zero in MATLAB) and so it is not the case that all of the elements being tested are non-zero. So MATLAB would consider if [1 5] > 3 to be false and not do the statement.

The same thing happens for while

So when some of your values are > 126 but not all of them are, then MATLAB would not execute the body of the loop.

You can change this by using

 while any(value(i)>126)

but be careful because it would proceed on to subtract 95 from all of the items in value(i)

Vectorizing is a good thing more often than not, but when you vectorize you need to be very careful with if and while . You should read about logical indexing

[Travis Ha]

After editing my code, all of the tests were passed. Thanks for the help!

[Santhosh Kumar]

why are we using + or - 95 in the code?

[Walter Roberson]

"The ASCII codes of these are 32 through 126"

length(32:126)

ans = 95

so each time you run off one end of the list of ASCII codes, to wrap around once, you need to adjust your counter by 95.

[Jobin Geevarghese Thampi]

@Walter Roberson WHY ARE WE DOING + OR-95 WHAT IS ITS USE?

[Walter Roberson]

@Jobin Geevarghese Thampi

That is @Marilou's code, not mine.

Suppose the input were

char(126)

ans = '~'

and you were asked to shift it forward by 2 positions. What is the expected output? We read the problem requirements:

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

Wrap around in that forward direction means that the character after char(126) should be char(32) then char(33), then char(34) and so on. Thus if we started with ~ (char 126) and shifted forward two, we need to end up with char(33)

char(34)

ans = '"'

which is

original = 126

original = 126

shift = 2

shift = 2

target = 33

target = 33

amount_to_go_back = original + shift - target

amount_to_go_back = 95

which also happens to be

length(32:126)

ans = 95

[Jobin Geevarghese Thampi]

what does value=M+N means?

[Jobin Geevarghese Thampi]

and for caesar('ABCD',3)

for=1:length(value) means 1:4 right?

[Walter Roberson]

@Jobin Geevarghese Thampi

Yes.

Answer 3

[Wilver Sánchez]

function coded = caesar(text,amound)
n=amound - 95 * fix(amound/95);
v=double(text)+n;
v(v<32)=126-(31-v(v<32));
v(v>126)=32+(-127+v(v>126));
coded=char(v);
end

[Wilver Sánchez]

I've wrote this code it solves de problem in a different way that the ones I've seen in the previous answers, I hope it can help someone.

[Raffael Leobino]

genius move

Answer 4

[Pavel Radko]

Thanks to a person who told about circshift function. I've been tried several hours to solve this task without that function.

So finaly I've passed all tests. And final code is much shorter and elegant as I have at today's morning ))

It has only 4 lines including the "end".

The main idea is to shift character table, but not the symbols of input.

% Write a function "caesar" that uses as input "array" - array 
% of ASCII table characters, and "shift" - the value (integer) of shifting the "array" elements
% via ASCII table (from 32nd to 126th)
function coded = caesar (array,shift)
shifted_array=circshift(char(32:126),-shift);
% we shift (roll) ASCII characters from 32 to 126 on the "shift" amount
% note that we use "-shift", because we shift the character table but not
% the characters in our "array"
% as output we get all ASCII characters from 32 to 126 but shifted (rolled)
coded = shifted_array(double(array)-31)
% double(array) - gets array of numbers that correspond to ASCII character
% table
% (double(array)-31) - this outs array of numbers with caracter indices
% shifted by -31
% "-31" because we use "shifted_array" that hasnt ASCII characters from 1 to 31
% shifted_array() - uses array of numbers in parentheses as shifted table
% indices and outputs corresponding characters from it
end

[Rik]

Well done, you actually try to educate future readers instead of treating this forum as a homework submission system. Have an upvote from me for your well-commented function and code.

There are only two things that would improve this function: documentation (a one-line description of the function, followed by an explanation of the input and output) and input validation.

[Sayand Sathish]

By far the best solution on this page

[THIERNO AMADOU MOUCTAR BALDE]

Thanks sir, that's the best code and the shortest

[JPS]

thanks man!

[Qaiser khan Bozdar]

Nice solution I got it.

[Sai Krishna Praneeth Duggirala]

what is the need of using double ??

[Nikhil Sharma]

function coded = caesar(x,y)
b= double(x)
m = mod(y, 95)
c= b+m
if c>126
        c= c-95;
elseif c<32
        c = c+95;
end
        coded=char(c)
end

[Walter Roberson]

@Nikhil Sharma

That code can fail if x is a vector, which is the expected case. Consider for example

caeser( char(124:126), 1)

double(char(124:126)) would be [124, 125, 126]. Add 1 to that to get c = [125, 126, 127]. Now you test

if c>126

but c is a vector, and the [125 126] part is not greater than 126, so the if will fail because the test will produce [false,false,true] and if needs the values to be all non-zero for the test to succeed.

Answer 5

[Guillaume]

Use mod or rem to constrain values between 0 and a maximum, with wrap-around.e.g:

>> mod(0:51, 26)
ans =
  Columns 1 through 21
     0     1     2     3     4     5     6     7     8     9    10    11    12    13    14    15    16    17    18    19    20
  Columns 22 through 42
    21    22    23    24    25     0     1     2     3     4     5     6     7     8     9    10    11    12    13    14    15
  Columns 43 through 52
    16    17    18    19    20    21    22    23    24    25

You can see that values 26, 27, ... go back to 0, 1, ...

Add/subtract some offsets to do the same for values in the range 32:126

[mayank ghugretkar]

sorry but its not working here...

tried using a for loop but ...no required output.

can u simplify more ?? or be a bit more specific here?

[Guillaume]

I'm sorry but I don't give solutions to homework. That would be a disservice to you as going through the process of finding the solution is how you learn to solve problems.

If you have a vector of numbers taken from the set 0:25, e.g.

v = [0 5 10 13 20];

And add 15 to each number

>> v = v + 15
v =
    15    20    25    28    35

To force the result to wrap around back to your initial range (0:25), you'd use mod:

>> mod(v, 25)
ans =
    15    20     0     3    10

Apply the same to your range (after shifting it so that it starts to 0 and shifting it back afterward).

Loops are not needed for this.

[JPS]

mod is great when moving forward sir... what about a negative shift...?

[Walter Roberson]

mod() works for negative shifts too

S = 'xyla'

S = 'xyla'

shift = 5

shift = 5

char('a' + mod(S - 'a' + shift,26))

ans = 'cdqf'

char('a' + mod(S - 'a' - shift,26))

ans = 'stgv'

[Manuel Rodríguez Flores]

Hello, I've tried this but some of the values in my vector stop appearing or changed to another row when the output is given. I would really appreciate any advice. The code is:

function coded = caesar(v,m)
v = double(v);
v = v + m;
for r = 1:size(v,2) %I tried this to solve the characters dissapearing
    v(1,r) = mod(v(1,r),95);
end
coded = char(v);
end

Answer 6

[Zeyuan Cao]

I came up with an approach which uses logical indexing instead of if statement

function coded=caesar(str,n)
str1=double(str);
m=n-95*floor(n/95);
codedstr1=str1+m;
codedstr1(codedstr1>=127)=codedstr1(codedstr1>=127)-127+32;
coded=char(codedstr1);
end

[Sahil]

Dude this only half the solution you missed " message + n < 32 " condition

function coded = caesar(message , n)
msg = double(message);
m = mod(n, 95);
coded_msg = msg + m;
coded_msg(coded_msg > 126) = coded_msg(coded_msg > 126) - 127 + 32;
coded_msg(coded_msg < 32) = coded_msg(coded_msg < 32) + 127 -32;
coded =char(coded_msg);
end

Answer 7

[Sahil]

function coded = caesar(message , n)
msg = double(message);
m = mod(n, 95); % this contricts the key within the range 
coded_msg = msg + m;
coded_msg(coded_msg > 126) = coded_msg(coded_msg > 126) - 95;
coded_msg(coded_msg < 32) = coded_msg(coded_msg < 32) + 95;
coded =char(coded_msg);
end

[Capulus_love]

thanks. i miss the sentence

m = mod(n, 95); % this contricts the key within the range

now i pass this question! :)

[ANDIE MEDDAUGH]

Why 95?

[Walter Roberson]

@ANDIE MEDDAUGH

Read the problem description:

"The function needs to work with all the visible ASCII characters from space to ~. The ASCII codes of these are 32 through 126"

Now calculate:

length(32:126)

ans = 95

[Suleman]

% this contricts the key within the range

you mean constrict ?

very good solution

Answer 8

[Cyrus David Pastelero]

%This is my aproach to the problem.
function coded = caesar(arr, num)
    size = strlength(arr);
    coded = arr+num
    for i = 1:size
        while coded(i)> 126 
            coded(i) = coded(i) - 95;
        end
        while coded(i) < 32
            coded(i) = coded(i) + 95;
        end
    end
    coded = char(coded);
end

[Santhosh Kumar]

why are we using + or - 95 in the code ?

Answer 9

[CCF2017 MIT]

This problem is asking you to shift the character variable by a given element n

the word wrap means that if the ASCII code of your character exceeds 32 or 126 you need to circle back again .

For example

if ASCII code is 97 and n (shift variable) is 45 so your ASCII code is 142 which exceeds 126. So you need to subtract 126 from 142

142-126, and add the net result to 31.

you need'nt do all that..... use the function called circshift

so i defined a character array from 32 to 126 which is the required ascii range

ch=char(32:126)

these are the characters.

ch =

    ' !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~'

and when i use the circshift command

ch_shift_pos=circshift(ch,2)
ch_shift_pos =

    '}~ !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|'
ch_shift_neg=circshift(ch,-2)
ch_shift_neg=

    '"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~ !'

Notice how the characters have shifted by 2 positions without you having to manually keep it within its range.

now if i want to find a character and its corresponding encrypted/shifted value i simply transfer the index since both ch and ch_shift are of the same size

so for example: if i want to find the encryption character of a , i first find the index of a in the 'ch' array and store it in a variable called x

    x=strfind(ch,'a')
    x =

    66

and then i use that index to find the encryption in the shifted array

ch_shift_pos(x)

ans =

    '_'
ch_shift_neg(x)

ans =
    'c'

There! thats your answer. As simple as that. But i had to rack my brains for it. :P

[Guillaume]

That's certainly one way of doing it, and it's not overly complicated.

Note that you don't need strfind and using strfind would force you to loop over the individual characters of the message to encrypt. Using the 2nd output of ismember would allow you to look up the position of all the message characters at once, so overall you'd need just 3 lines of code for your encryption function.

Still not as efficient as using mod but not bad.

[CCF2017 MIT]

i dont want to be arguing about what is efficient and what is not, and which one is complicated. what i certainly dont agree with is having an answer and not explaning properly. literally everyone in the comments section is asking for the meaning of your answer, yet you dont want to ellaborate further.

i am a beginner in matlab programming and so are many others, you must understand that not everyone has access to the best resources and not everyone has the knowledge or the skill that you have acquired . Hence you must try and be a little more specific and not take it for granted that someone knows. because it can be easy for you, and it can be complicated for others.

[Guillaume]

I have explained how to do it in various comments here. I'm not sure how I can explain it more without giving the solution away.

In one comment, I wrote that all that is needed is: "a subtraction by an integer, a mod, an addition by the same integer" (and a conversion to char afterwards).

You have a message with a set of numbers (characters) between two values a and b. Shift that set of numbers so that it is between 0 and b-a. Add your caesar shift. This may underflow 0 or overflow b-a. Apply mod so that it wraps back between 0 and b-a. Reverse your original shift so that the numbers are once agian between a and b.

Answer 10

[Rahul Gulia]

function coded = caesar(str,n)
num1 = double(str);     %Converting string to double to make the defined shifts
for i = 1 : length(num1)     
    if num1(i) + n > 126        % If ASCII value goes beyond 126
        m = num1(i)-126+n;
        p = 31+m;
        num1(i) = p;
        
    elseif num1(i)+n < 32     % If ASCII value goes below 32
        m = 32 - num1(i) + n;
        p = 126 - m;
        num1(i) = p;
        
    else m = num1(i) + n;     % In a normal condition
        num1(i) = m;
    end
    
    code(i) = num1(i);
end
coded = char(code);

I have written this code. Can anyone please expain as what is wrong in here? I know i have made a mistake. But i am not able to figure it out.

Thanks in advance.

[Guillaume]

What makes you think you've made an error?

[Mukti Awad]

function coded = caesar(str,n)
num1 = double(str);     %Converting string to double to make the defined shifts
for i = 1 : length(num1)     
    if num1(i) + n > 126        % If ASCII value goes beyond 126
        m = num1(i)-126+n;
        p = 31+m;
        num1(i) = p;
        
    elseif num1(i)+n < 32     % If ASCII value goes below 32
        m = 32 - num1(i) + n;
        p = 126 - m;
        num1(i) = p;
        
    else m = num1(i) + n;     % In a normal condition
        num1(i) = m;
    end
    
    code(i) = num1(i);
end
coded = char(code);

I am getting this error

Assessment: 0 of 2 Tests Passed

Submit More Info

• Assessment result: incorrectA few simple casesVariable coded has an incorrect value. caesar(' !"#$&()*+,-.0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[]^_`abcdefghijklmnopqrstuvwxyz{|}~',243) returned an incorrect value...
• Assessment result: incorrectRandom shiftsVariable coded has an incorrect value. caesar('MATLAB is fun!',105) returned an incorrect value...

[Kunjkumar Thummar]

Can you please explain beypnd 126 case and below 32 case?

[Robert Wadra]

Same error I am getting

[Walter Roberson]

Suppose n = 1000 and the character vector is 'a' (which is 97 decimal). num1 would become 97. num1(1)+1000 > 126, so m = 97-126+1000 would be m=971. Then p=31+971 gives p = 1002 . This is not the desired result.

The code needs to adjust num1+n to be between 32 and 126 (inclusive)

Answer 11

[shreyansh pitroda]

%% Function encode the code by shifting it by amount user as specified 

function [coded]= caesar(code , shift)  %% TAKES TWO VALUE CODE AND AMOUNT OF SHIFT 
A = double(code);
x = 1;
z = length(A);
z = z+ 1;
shift = shift - 95*(fix(shift/95));
code(1:end) = code(1:end) + shift;
while x ~= z                    %%used the while loop to provide count
if code(1,x)< 32                %%if the value is below 32
    A(1,x) = A(1,x) - 32;
    A(1,x) = A(1,x) + shift;
    A(1,x) = A(1,x) + 127;
elseif (code(1,x)>32)&&(code(1,x)<127) %% if value is between 32 and 127
    A(1,x) = A(1,x) + shift;
else                           %% if the value is greater than 127
    A(1,x) = A(1,x) - 127;
    A(1,x) = A(1,x) + shift;
    A(1,x) = A(1,x) + 32;
end
x= x + 1;
end
coded = char(A);          %% code print 
end

Answer 12

[Washida Kami]

%uses the mod function
function txt = caesar(txt,key)
    txt = double(txt) + key;
    first = double(' ');
    last = double('~');
    % use mod to shift the characters - notice the + 1
    % this is a common error and results in shifts 
    % being off by 1
    txt = char(mod(txt - first,last - first + 1) + first);
end

%uses the circshift function
function y = caesar2(ch, key)
    v = ' ' : '~';
    [~, loc] = ismember(ch, v);
    v2 = circshift(v, -key);
    y = v2(loc);
end

[Noor Ul Zain]

can someone please explain the mod function code, I also dont get why we add first, shouldnt we add first-1. Please please explain

[Walter Roberson]

Suppose txt == first, then txt-first is 0, and mod(0,something) is 0. Now suppose you had the first-1 that you propose, then the result would be first-1 . Clearly, though, it makes the most sense for the calculation to leave you within the first to last range, instead of before the range.

Answer 13

[Rajat Munjal]

function coded = caesar(ctbe,sa)
     dd = double(ctbe)
     if dd>=32 & dd<=126
        ss =dd +sa
        ss(ss<32) = rem((ss(ss<32)-32),95)+127
        ss(ss>126)=rem((ss(ss>126)-126),95)+31
        coded =char(ss);
     end
end

[Rajat Munjal]

Can someone please help me in finding the mistake ?

[Walter Roberson]

dd = double(ctbe)

ctbe will be a vector of char, so dd will be a vector of double.

     if dd>=32 & dd<=126

dd>=32 & dd<=126 would be a logical vector. When you test a non-scalar with if or while, it is considered true if all of the items being tested are non-zero (true). If even one of the entries was not within that range then the test would be considered false as a whole... and you have no else condition so nothing would be assigned to coded

Answer 14

[Olel Arem]

Short code with use of Logical Indexing:

function coded= caesar(string,shift)
mod_str=string+shift;
for i=1:length(mod_str)
    mod_str(mod_str<32)=mod_str(mod_str<32)+95;
    mod_str(mod_str>126)=mod_str(mod_str>126)-95;
end
coded=char(mod_str);

Answer 15

[Omkar Kadam]

function coded = caesar(V,N)
ascii = char(32:126);
coded1 = (double(V) + N - 31);
found = false;
ii = 1;
coded2 = [];
while ~(found)
    if ii < length(coded1)+1
        j = coded1(ii);
        ii = ii +1;
        while j < 32
            j = j + 126 - 31;
        end
        while j > length(ascii)
            j = j - length(ascii);
        end
        coded2 = abs([coded2,j]);
    else
        found = true;
        break;
    end
end
coded = ascii(coded2); %this is 100% working code.

Answer 16

[GAURAV RAJ]

help me in this . i wrote this code but i am getting error please tell me what's wrong in this

function y=caesar(a,b)
    q=double(a);    
    for i=1:length(a)
        d(i)=q(i)+b;
        if d(i)>=32;
            e(i)=rem(d(i),126);
        else
            e(i)=95+d(i);
        end
        if e(i)>=32 ;         
            y(i)=char(e(i));
        elseif e(i)==0;
            y(i)=char(126);
        else
            e(i)=e(i)+31;
            y(i)=char(e(i));
        end                
    end   
end

[Walter Roberson]

Suppose b is -200 and q is double('A') = 65.

d = 65-200 -> d = -135

-135 >= 32 is false, so

e = 95 + -135 = -40

-40 >= 32 is false

-40 == 0 is false

e(i) = -40 + 31 = -9

y(i) = char(-9) which is same as char(0)

Answer 17

[Arafat Roney]

function coded=caesar(c,s)
n=mod(s,95);
sc=c+n;
l=length(sc);
w=[]; 
    for i=1:l
        if sc(i)>126
            p=31+(sc(i)-126);
        elseif sc(i)<32
               p=126-abs(sc(i)-31);
        else
            p=sc(i);
        end
        w=[w p];
    end
    coded=char(w);
end

Answer 18

[Shandilya Kiran Bhatt]

The code below is a long one but it is using a while loop and if you read it, it is an easy one and it is correct for any random shifts.

function coded = caesar(A,n)
a = double(A);
z = a + n;
for i =1: length(a)
        if z(i)>126
        b = z(i) - 126;
            if b <=95
            z(i) = 31 + b;
            else
                while b > 95
                    b = b-95;
                end
                z(i) = 31 + b;
            end
        end
            if z(i) < 32 
                c = 32 - z(i);
                if c <= 95
                z(i) = 127 - c;
                else
                    while c >95
                        c = c - 95;
                    end
                    z(i) = 127 -c;
                end
            end
end
encrypted_code = z;
coded = char(encrypted_code);
end

Answer 19

[SAMARTH MAHESHKUMAR GEMLAWALA]

This code is quite lenghty, but logic that i have used is quite simple understand

function coded = caesar(A, n)
a = double(A)
ele=size(a)
for i=1:ele(1,2)
    if n>=0
        for j=1:n
            a(i) = a(i)+1;
            if a(i)>126
            a(i)=32;
            end
        end
    end
    if n<0
        for j=1:abs(n)
            a(i) = a(i)-1;
            if a(i)<32
                a(i)=126;
            end
        end
    end
end
coded = char(a);
end

Answer 20

[Julian Veran]

function coded = caesar(M, n)
num = double(M);                        %Converts string into double
num2 = num;
N = n - 95 * fix(n/95);
for i = 1:length(num);  
    if  num(i) + N < 32                 %If ASCII value goes below 32
        num2(i) = 126 - (31- num(i) - N);
    elseif num(i) + N > 126             %If ASCII value goes beyond 126
        num2(i) = 32 + (num(i) + N -127);
    else 
        num2(i) = num(i) + N ;          %If ASCII value goes normal
    end
coded = char(num2);
end

[Tatiana Suaza Varela]

Hi! Sorry for the inconveniences, but please could you explain why we need to convert the string into double?

Answer 21

[Julian Veran]

(using mod function)

function txt = caesar(txt,key)
    txt = double(txt) + key;
    first = double(' ');
    last = double('~');
    % use mod to shift the characters - notice the + 1
    % this is a common error and results in shifts 
    % being off by 1
    txt = char(mod(txt - first,last - first + 1) + first);
end

(using circ shify function)

function y = caesar2(ch, key)
    v = ' ' : '~';
    [~, loc] = ismember(ch, v);
    v2 = circshift(v, -key);
    y = v2(loc);
end

[Shenaz Fathima]

I dont get the last line of ur code.. Can u explain it? (using mod function) What is the function of mod?

[Rik]

Have you read the documentation for the mod function?

doc mod

Answer 22

[Timothy Simon Thomas]

%% CAESAR's SIPHER
% CAESAR(message,code): Message is the message to be encripted
% CODE represents the ASCII shift
% Wrapping always enabled
function coded = caesar(message,code)
while(code>95)
    code=code-95;
end
while(code<-95)
    code=code+95;
end
message=message+code;                                                        %base case
message(message>126)=char(double(message(message>126))-95)                   %overshoot
message(message<32)=char(double(message(message<32))+95)                     %undershoot
coded=char(message);
end

Answer 23

[Taif Ahmed BIpul]

function coded=caesar(v,n)
x=double(v)+n;
q=x(x<32);
p=x(x>126);
while q<32;
    x(x<32)=x(x<32)+95;
    q=x(x<32);
end
while p>126;
    x(x>126)=x(x>126)-95;
    p=x(x>126);
end

coded=char(x);
end

Answer 24

[yazan ziyad]

here you go

function [coded]=caesar(a,shift)
    m=double(a)
    codedd=m+shift;
    for i=1:abs(shift)
        codedd(codedd<32)=127-(32-codedd(codedd<32));
        codedd(codedd>126)=31+(codedd(codedd>126)-126)
        coded=char(codedd)
    end
end

Answer 25

[SONU NIGAM]

function coded = caesar(char_vec,shift_amount)
char_value = char_vec+shift_amount;
for ii = 1:length(char_value)
    if char_value>126
        coded = char(char_value-95);
    elseif char_value<32
        coded = char(char_value+95);
    else
        coded = char(char_value);
    end
end
end

I got correct output but in the assignment when i run this program it shows error...What fault i did i m unable to notice,if anyone can explain me then plz help me.

Answer 26

[Soroush sa]

I'm beginner and I have written this code. Can anybody help me by expaining that what is wrong in here?

function coded = caesar(string,shift)
    double_A = double(string);
    position = double_A + shift;
    for ii = 1:length(position)
        if position > 126
            new_position = position - 95;
        elseif position < 32
            new_position = position + 95;
        else
            new_position = position;
        end
    end
    coded = char(new_position);
end

[Walter Roberson]

Consider what would happen if the shift were (say) 450 ?

Answer 27

[Sumit Kumar Sharma]

function coded=caesar(a,b)
x=double(a);
k=mod(b,95);
q=[];
for j=1:length(x)
    p=x(j)+k;
    if p<=126 && p>=32
        q=[q p];
    elseif p>126
        r=p-95;
        q=[q r]    ;                                                                                                                             
    elseif p<32
        s=p+95;
        q=[q s];