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caesar cyphor encryption problem .
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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
16 Comments
Danial Ahmad
on 28 Sep 2020
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
on 28 Sep 2020
@Danial, which code are you talking about? Sonu already mentioned their code doesn't work.
Accepted Answer
Yitong Liu
on 24 Aug 2019
Edited: Yitong Liu
on 24 Aug 2019
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.
30 Comments
Walter Roberson
on 14 Aug 2021
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
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.
More Answers (41)
Marilou
on 17 Oct 2019
Edited: DGM
on 26 Feb 2023
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);
15 Comments
Jobin Geevarghese Thampi
on 21 Mar 2022
and for caesar('ABCD',3)
for=1:length(value) means 1:4 right?
Wilver Sánchez
on 7 Feb 2020
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
2 Comments
Wilver Sánchez
on 7 Feb 2020
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.
Pavel Radko
on 11 Aug 2020
Edited: Pavel Radko
on 13 Aug 2020
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
8 Comments
Nikhil Sharma
on 18 Jul 2021
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
on 18 Jul 2021
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.
Guillaume
on 12 Jun 2019
>> 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
5 Comments
Walter Roberson
on 9 Jan 2021
mod() works for negative shifts too
S = 'xyla'
shift = 5
char('a' + mod(S - 'a' + shift,26))
char('a' + mod(S - 'a' - shift,26))
Manuel Rodríguez Flores
on 4 Aug 2021
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
Zeyuan Cao
on 7 Feb 2020
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
1 Comment
Sahil
on 19 Mar 2020
Edited: DGM
on 26 Feb 2023
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
Sahil
on 19 Mar 2020
Edited: DGM
on 26 Feb 2023
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
4 Comments
Walter Roberson
on 22 Jul 2021
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)
Suleman
on 25 Feb 2023
% this contricts the key within the range
you mean constrict ?
very good solution
Cyrus David Pastelero
on 8 Jul 2020
Edited: Cyrus David Pastelero
on 8 Jul 2020
%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
1 Comment
CCF2017 MIT
on 2 Jul 2019
Edited: CCF2017 MIT
on 2 Jul 2019
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
3 Comments
CCF2017 MIT
on 2 Jul 2019
Edited: CCF2017 MIT
on 2 Jul 2019
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
on 2 Jul 2019
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.
Rahul Gulia
on 22 Jul 2019
Edited: Guillaume
on 22 Jul 2019
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.
5 Comments
Walter Roberson
on 12 Jul 2020
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)
shreyansh pitroda
on 30 Mar 2020
%% 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
0 Comments
Washida Kami
on 31 Mar 2020
%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
2 Comments
Noor Ul Zain
on 20 Aug 2020
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
on 20 Aug 2020
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.
Rajat Munjal
on 13 Apr 2020
Edited: DGM
on 26 Feb 2023
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
2 Comments
Walter Roberson
on 13 Apr 2020
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
Olel Arem
on 30 Apr 2020
Edited: Olel Arem
on 30 Apr 2020
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);
0 Comments
Omkar Kadam
on 9 May 2020
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.
0 Comments
GAURAV RAJ
on 10 May 2020
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
1 Comment
Walter Roberson
on 11 May 2020
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)
Arafat Roney
on 11 May 2020
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
0 Comments
Shandilya Kiran Bhatt
on 12 May 2020
Edited: Walter Roberson
on 12 May 2020
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
0 Comments
SAMARTH MAHESHKUMAR GEMLAWALA
on 15 May 2020
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
0 Comments
Julian Veran
on 18 May 2020
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
1 Comment
Tatiana Suaza Varela
on 19 Dec 2020
Hi! Sorry for the inconveniences, but please could you explain why we need to convert the string into double?
Julian Veran
on 18 May 2020
(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
2 Comments
Shenaz Fathima
on 15 Aug 2020
I dont get the last line of ur code.. Can u explain it? (using mod function) What is the function of mod?
Rik
on 15 Aug 2020
Have you read the documentation for the mod function?
doc mod
Timothy Simon Thomas
on 19 May 2020
%% 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
0 Comments
Taif Ahmed BIpul
on 21 May 2020
Edited: DGM
on 26 Feb 2023
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
0 Comments
yazan ziyad
on 29 May 2020
Edited: DGM
on 26 Feb 2023
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
0 Comments
SONU NIGAM
on 29 May 2020
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.
0 Comments
Soroush sa
on 30 May 2020
Edited: DGM
on 26 Feb 2023
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
1 Comment
Sumit Kumar Sharma
on 4 Jun 2020
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];
end
end
coded=char(q);
end
0 Comments
Vistasp Edulji
on 22 Jun 2020
A much shorter solution is possible using logical arrays.
function coded =caesar(str, n)
coded = str + n;
while ( sum(coded >= 127) > 0 || sum(coded <= 31) >0 )
coded(coded >= 127) = 31 + (coded(coded>=127)-126);
coded(coded <= 31) = 127 - (32-coded(coded<=31));
end
coded = char(coded);
The while loop condition simply ensures that there is no overflow after each round of correction
The important thing is your output should be a string