Rot-13
From Rosetta Code
Programming Task
This is a programming task. It lays out a problem which Rosetta Code users are encouraged to solve, using languages they know.
The "rot-13" encoding is commonly known from the early days of Usenet "Netnews" as a way of obfuscating text to prevent casual reading of spoilers or other potentially offensive material. Many news reader and mail user agent programs have built-in "rot-13" encoder/decoders or have the ability to feed a message through any external utility script for performing this (or other) actions.
The definition of the rot-13 function is to simply replace every letter of the ASCII alphabet with the letter which is "rotated" 13 characters "around" the 26 letter alphabet from it's normal cardinal position (wrapping around from "z" to "a" as necessary). Thus the letters "abc" become "nop" and so on. Technically rot-13 is a "monoalphabetic substitution cipher" will a trivial "key". A proper implementation should work on upper and lower case letters, preserve case, and pass all non-alphabetic characters in the input stream through without alteration.
Contents |
[edit] Ada
with Ada.Text_IO.Text_Streams; use Ada.Text_IO.Text_Streams;
with Ada.Strings.Maps; use Ada.Strings.Maps;
with Ada.Command_Line; use Ada.Command_Line;
procedure Rot_13 is
From_Sequence : Character_Sequence := "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
Result_Sequence : Character_Sequence := "nopqrstuvwxyzabcdefghijklmNOPQRSTUVWXYZABCDEFGHIJKLM";
Rot_13_Mapping : Character_Mapping := To_Mapping(From_Sequence, Result_Sequence);
In_Char : Character;
Stdio : Stream_Access := Stream(Ada.Text_IO.Standard_Input);
Stdout : Stream_Access := Stream(Ada.Text_Io.Standard_Output);
Input : Ada.Text_Io.File_Type;
begin
if Argument_Count > 0 then
for I in 1..Argument_Count loop
begin
Ada.Text_Io.Open(File => Input, Mode => Ada.Text_Io.In_File, Name => Argument(I));
Stdio := Stream(Input);
while not Ada.Text_Io.End_Of_File(Input) loop
In_Char :=Character'Input(Stdio);
Character'Output(Stdout, Value(Rot_13_Mapping, In_Char));
end loop;
Ada.Text_IO.Close(Input);
exception
when Ada.Text_IO.Name_Error =>
Ada.Text_Io.Put_Line(File => Ada.Text_Io.Standard_Error, Item => "File " & Argument(I) & " is not a file.");
when Ada.Text_Io.Status_Error =>
Ada.Text_Io.Put_Line(File => Ada.Text_Io.Standard_Error, Item => "File " & Argument(I) & " is already opened.");
end;
end loop;
else
while not Ada.Text_Io.End_Of_File loop
In_Char :=Character'Input(Stdio);
Character'Output(Stdout, Value(Rot_13_Mapping, In_Char));
end loop;
end if;
end Rot_13;
[edit] BASIC
Works with: QuickBasic version 4.5
CLS
INPUT "Enter a string: ", s$
ans$ = ""
FOR a = 1 TO LEN(s$)
letter$ = MID$(s$, a, 1)
char$ = ""
IF letter$ >= "A" AND letter$ <= "Z" THEN
char$ = CHR$(ASC(letter$) + 13)
IF char$ > "Z" THEN char$ = CHR$(ASC(char$) - 26)
ELSEIF letter$ >= "a" AND letter$ <= "z" THEN
char$ = CHR$(ASC(letter$) + 13)
IF char$ > "z" THEN char$ = CHR$(ASC(char$) - 26)
ELSE
char$ = letter$
END IF
ans$ = ans$ + char$
NEXT a
PRINT ans$
[edit] Befunge
~:"z"`#v_:"m"`#v_:"`"` |> :"Z"`#v_:"M"`#v_:"@"`|> : 0 `#v_@v-6-7< > , < <+6+7 <<v
[edit] C
#include<stdio.h>
#include<stdlib.h>
#include<ctype.h>
#define MAXLINE 1024
char *rot13(char *s)
{
char *p=s;
int upper;
while(*p) {
upper=toupper(*p);
if(upper>='A' && upper<='M') *p+=13;
else if(upper>='N' && upper<='Z') *p-=13;
++p;
}
}
return s;
}
void rot13file(FILE *fp)
{
static char line[MAXLINE];
while(fgets(line, MAXLINE, fp)>0) fputs(rot13(line), stdout);
}
int main(int argc, char *argv[])
{
int n;
FILE *fp;
if(argc>1) {
for(n=1; n<argc; ++n) {
if(!(fp=fopen(argv[n], "r"))) {
fprintf(stderr, "ERROR: Couldn\'t read %s\n", argv[n]);
exit(EXIT_FAILURE);
}
rot13file(fp);
fclose(fp);
}
} else rot13file(stdin);
return EXIT_SUCCESS;
}
[edit] C++
#include <iostream>
#include <istream>
#include <ostream>
#include <fstream>
#include <cstdlib>
#include <string>
// the rot13 function
std::string rot13(std::string s)
{
static std::string const
lcalph = "abcdefghijklmnopqrstuvwxyz",
ucalph = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
std::string result;
std::string::size_type pos;
result.reserve(s.length());
for (std::string::iterator it = s.begin(); it != s.end(); ++it)
{
if ( (pos = lcalph.find(*it)) != std::string::npos )
result.push_back(lcalph[(pos+13) % 26]);
else if ( (pos = ucalph.find(*it)) != std::string::npos )
result.push_back(ucalph[(pos+13) % 26]);
else
result.push_back(*it);
}
return result;
}
// function to output the rot13 of a file on std::cout
// returns false if an error occurred processing the file, true otherwise
// on entry, the argument is must be open for reading
int rot13_stream(std::istream& is)
{
std::string line;
while (std::getline(is, line))
{
if (!(std::cout << rot13(line) << "\n"))
return false;
}
return is.eof();
}
// the main program
int main(int argc, char* argv[])
{
if (argc == 1) // no arguments given
return rot13_stream(std::cin)? EXIT_SUCCESS : EXIT_FAILURE;
std::ifstream file;
for (int i = 1; i < argc; ++i)
{
file.open(argv[i], std::ios::in);
if (!file)
{
std::cerr << argv[0] << ": could not open for reading: " << argv[i] << "\n";
return EXIT_FAILURE;
}
if (!rot13_stream(file))
{
if (file.eof())
// no error occurred for file, so the error must have been in output
std::cerr << argv[0] << ": error writing to stdout\n";
else
std::cerr << argv[0] << ": error reading from " << argv[i] << "\n";
return EXIT_FAILURE;
}
file.clear();
file.close();
if (!file)
std::cerr << argv[0] << ": warning: closing failed for " << argv[i] << "\n";
}
return EXIT_SUCCESS;
}
[edit] D
Implement a Rot-13 function.
module rot13 ; import std.stdio ; version(D_Version2) { import std.algorithm ; } char rot13char(char t) { ubyte c = (t & 0x9f) - 1 ; if (c > 25 || (t & 0x40) == 0 ) return t ; c = (c + 13) % 26 ; // that's why Rot-13 :) return (t & 0x60) | (c + 1) ; } string rot13(string s) { string t ; foreach(c ; s) t ~= rot13char(c) ; return t ; } void main(string[] args) { string text = "abc! ABC!" ; writefln(rot13(text)) ; writefln(rot13("abcdefghijklmnopqrstuvwxyz"~ "ABCDEFGHIJKLMNOPQRSTUVWXYZ")) ; version(D_Version2) { writefln(map!(rot13char)(text)) ; writefln(map!(rot13char)("abcdefghijklmnopqrstuvwxyz"~ "ABCDEFGHIJKLMNOPQRSTUVWXYZ")) ; } }
A simpler version (D V.1):
import std.stdio, std.string; void main() { auto r13 = letters.maketrans(uppercase[13..$] ~ uppercase[0..13] ~ lowercase[13..$] ~ lowercase[0..13]); writefln("This is the 1st test!".translate(r13, null)); }
[edit] Forth
A simple version, using nested conditionals.
: r13 ( c -- o )
dup 32 or \ tolower
dup [char] a [char] z 1+ within if
[char] m > if -13 else 13 then +
else drop then ;
A table driven version which should be more efficient. The mechanism is flexible enough to express any sort of transform.
: ,chars ( end start -- ) do i c, loop ; : xlate create does> ( c -- c' ) + c@ ; xlate rot13 char A 0 ,chars char Z 1+ char N ,chars char N char A ,chars char a char Z 1+ ,chars char z 1+ char n ,chars char n char a ,chars 256 char z 1+ ,chars : rot13-string ( addr len -- ) over + swap do i c@ rot13 i c! loop ; : .rot13" ( string -- ) [char] " parse 2dup rot13-string type ; .rot13" abjurer NOWHERE" \ nowhere ABJURER
[edit] Fortran
Works with: Fortran version 90 and later
MODULE ROT13
IMPLICIT NONE
CHARACTER(80) :: teststr = "ABCDEFGHIJKLMNOPQRSTUVWXYZ - abcdefghijklmnopqrstuvwxyz"
CONTAINS
SUBROUTINE ROT_13(s)
CHARACTER(*), INTENT(in out) :: s
INTEGER :: i
DO i = 1, LEN(s)
SELECT CASE (s(i:i))
CASE ("A":"M")
s(i:i) = ACHAR(IACHAR(s(i:i))+13)
CASE ("N":"Z")
s(i:i) = ACHAR(IACHAR(s(i:i))-13)
CASE ("a":"m")
s(i:i) = ACHAR(IACHAR(s(i:i))+13)
CASE ("n":"z")
s(i:i) = ACHAR(IACHAR(s(i:i))-13)
END SELECT
END DO
END SUBROUTINE ROT_13
END MODULE ROT13
PROGRAM Example
USE ROT13
CALL ROT_13(teststr)
WRITE(*,*) teststr
CALL ROT_13(teststr)
WRITE(*,*) teststr
END PROGRAM Example
Ouput
NOPQRSTUVWXYZABCDEFGHIJKLM - nopqrstuvwxyzabcdefghijklm ABCDEFGHIJKLMNOPQRSTUVWXYZ - abcdefghijklmnopqrstuvwxyz
[edit] Haskell
Straightforward implementation by checking multiple cases:
import Data.Char rot13 :: Char -> Char rot13 c | c < 'A' = c | c < 'N' = chr (ord c + 13) | c <= 'Z' = chr (ord c - 13) | c < 'a' = c | c < 'n' = chr (ord c + 13) | c <= 'z' = chr (ord c - 13) | otherwise = c
To wrap that as an utility program, here's a quick implementation of a general framework:
import System.Environment import System.IO import System.Directory import Control.Monad hInteract :: (String -> String) -> Handle -> Handle -> IO () hInteract f hIn hOut = hGetContents hIn >>= hPutStr hOut . f processByTemp :: (Handle -> Handle -> IO ()) -> String -> IO () processByTemp f name = do hIn <- openFile name ReadMode let tmp = name ++ "$" hOut <- openFile tmp WriteMode f hIn hOut hClose hIn hClose hOut removeFile name renameFile tmp name process :: (Handle -> Handle -> IO ()) -> [String] -> IO () process f [] = f stdin stdout process f ns = mapM_ (processByTemp f) ns
Then the wrapped program is simply
main = do names <- getArgs process (hInteract (map rot13)) names
Note that the framework will read the file lazily, which also provides buffering.
[edit] J
rot13=: (a.,~a.{~,65 97+/26|13+i.26) {~ (a.,~a.{~,65 97+/i.26) i. ]
For example:
rot13 'abc! ABC!' nop! NOP!
Compare with the solution to the Change String Case task.
[edit] Java
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStreamReader;
public class ROT13{
public static void main(String[] args){
BufferedReader in;
if(args.length >= 1){
for(String file: args){
try{
in= new BufferedReader(new FileReader(file));
String line;
while((line= in.readLine()) != null){
System.out.println(convert(line));
}
}catch(FileNotFoundException e){
e.printStackTrace();
}catch(IOException e){
e.printStackTrace();
}
}
}else{
try{
in= new BufferedReader(new InputStreamReader(System.in));
String line;
while((line= in.readLine()) != null){
System.out.println(convert(line));
}
}catch(IOException e){
e.printStackTrace();
}
}
}
public static String convert(String msg){
String retVal= "";
for(char a: msg.toCharArray()){
if(a >= 'A' && a <= 'Z'){
a+= 13;
if(a > 'Z') a-= 26;
}else if(a >= 'a' && a <= 'z'){
a+= 13;
if(a > 'z') a-= 26;
}
retVal+= a;
}
return retVal;
}
}
[edit] JavaScript
var rot13Str = "nopqrstuvwxyzabcdefghijklmNOPQRSTUVWXYZABCDEFGHIJKLM";
var plainStr = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
function rot13(s) {
var a = [];
for (var i=0; i<s.length; i++) {
var c = s.charAt(i);
var found = plainStr.indexOf(c);
a.push(found<0 ? c : rot13Str.charAt(found));
}
return a.join('');
}
alert( rot13("ABJURER nowhere") ); // NOWHERE abjurer
[edit] OCaml
Straightforward implementation for characters by using character range patterns:
let rot13 c = match c with 'A'..'M' | 'a'..'m' -> char_of_int (int_of_char c + 13) | 'N'..'Z' | 'n'..'z' -> char_of_int (int_of_char c - 13) | _ -> c
We provide a function for converting whole strings:
let rot13_str s = let len = String.length s in let result = String.create len in for i = 0 to len - 1 do result.[i] <- rot13 s.[i] done; result
[edit] Perl
sub rot13 {
$string = shift;
$string =~ tr/[A-Z][a-z]/[N-ZA-M][n-za-m]/;
return $string;
}
$alpha = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz';
print rot13($alpha), "\n";
Output:
NOPQRSTUVWXYZABCDEFGHIJKLMnopqrstuvwxyzabcdefghijklm
[edit] Pop11
In Pop11 characters are just integers, so we can use integer comparisons and arithmetic (assuming ASCII based encoding).
define rot13(s);
lvars j, c;
for j from 1 to length(s) do
s(j) -> c;
if `A` <= c and c <= `M` or `a` <= c and c <= `m` then
c + 13 -> s(j);
elseif `N` <= c and c <= `Z` or `n` <= c and c <= `z` then
c - 13 -> s(j);
endif;
endfor;
s;
enddefine;
rot13('NOPQRSTUVWXYZABCDEFGHIJKLMnopqrstuvwxyzabcdefghijklm') =>
[edit] Python
Python has built-in rot13 encoding and decoding:
>>> u'foo'.encode('rot13')
'sbb'
>>> 'sbb'.decode('rot13')
u'foo'
Here is an implementation:
#!/usr/bin/env python
import string
def rot13(s):
"""Implement the rot-13 encoding function: "rotate" each letter by the
letter that's 13 steps from it (wrapping from z to a)
"""
return string.translate( s,
string.maketrans(
string.uppercase + string.lowercase,
string.uppercase[13:] + string.uppercase[:13] +
string.lowercase[13:] + string.lowercase[:13]
)
)
if __name__ == "__main__":
"""Peform line-by-line rot-13 encoding on any files listed on our
command line or act as a standard UNIX filter (if no arguments
specified).
"""
import fileinput
for line in fileinput.input():
print rot13(line), # (Note the trailing comma; avoid double-spacing our output)!
The string.translate() and string.maketrans() functions make the function's definition almost trivial. It's a one-line function with some line wrapping for legibility. The fileinput module similarly makes the wrapper functionality trivial to implement. (This implementation is about seven logical lines long).
[edit] Seed7
This rot13 program reads from standard input and writes to standard output:
$ include "seed7_05.s7i";
const proc: main is func
local
var char: ch is ' ';
begin
ch := getc(IN);
while not eof(IN) do
if (ch >= 'a' and ch <= 'm') or (ch >= 'A' and ch <= 'M') then
ch := chr(ord(ch) + 13);
elsif (ch >= 'n' and ch <= 'z') or (ch >= 'N' and ch <= 'Z') then
ch := chr(ord(ch) - 13);
end if;
write(ch);
ch := getc(IN);
end while;
end func;
[edit] UNIX Shell
[edit] Bourne Shell
#!/bin/sh
function rot13 () {
tr '[a-m][n-z][A-M][N-Z]' '[n-z][a-m][N-Z][A-M]'
}
[ "$#" -lt 1 ] && {
rot13
} || for eachFile in "$@"; do
cat "$eachFile" | rot13
done
UNIX shell assumes availability of the standard UNIX utility commands (in the "coreutils" package on Linux systems, for example); thus the tr (translate) command is trivially provided with the proper arguments to perform the rotations. This example shows proper quoting around "$@" (magical argument list) and "$eachFile" such that this script work properly even if some of the files named on the command line contain embedded spaces or other such characters.
[edit] XSLT
Textual transforms are one of the domains XSLT was designed for.
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="text" />
<xsl:variable name="alpha">ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz</xsl:variable>
<xsl:variable name="rot13">NOPQRSTUVWXYZABCDEFGHIJKLMnopqrstuvwxyzabcdefghijklm</xsl:variable>
<xsl:template match="body">
<xsl:apply-templates/>
</xsl:template>
<xsl:template match="rot13">
<xsl:value-of select="translate(.,$alpha,$rot13)"/>
</xsl:template>
</xsl:stylesheet>
This will transform the input:
<body>The <rot13>Abjurer</rot13> was to be found <rot13>Nowhere</rot13>.</body>
into:
The Nowhere was to be found Abjurer.
Categories: Programming Tasks | Encryption | Ada | BASIC | Befunge | C | C++ | D | Forth | Fortran | Haskell | J | Java | JavaScript | OCaml | Perl | Pop11 | Python | Seed7 | UNIX Shell | XSLT
