Output the alphabet, the ALPHABET, or just a character

Question

The challenge is simple:

Write a function or program that takes an input x, and outputs the lower case alphabet if x is part of the lower case alphabet, outputs the upper case alphabet if x is part of the upper case alphabet and outputs just x if it's not part of either.

Rules:

• The input can be function argument or from STDIN
• The input will be any of the printable ASCII characters from 32 to 126 (space to tilde).
• The input may be inside quotation marks,'x' or "x", but remember that ' and " are valid input and should be supported.
• The input can be any of the letters in the alphabet, i.e. you can't assume it will be a or A.
• The output should be only one of the alphabets or the single symbol, but trailing newlines are OK.
• The letters in the alphabet should not be separated by spaces, commas or anything else.

Some examples:

F
ABCDEFGHIJKLMNOPQRSTUVWXYZ

z
abcdefghijklmnopqrstuvwxyz

"
"

    <- Input:  Space
    <- Output: Space

Shortest code in bytes win.

---

Optional but appreciated: If your language has an online interpreter, please also post a link so that it can be easily tested by others.

---

Leaderboard

The Stack Snippet at the bottom of this post generates the catalog from the answers a) as a list of shortest solution per language and b) as an overall leaderboard.

To make sure that your answer shows up, please start your answer with a headline, using the following Markdown template:

## Language Name, N bytes

where N is the size of your submission. If you improve your score, you can keep old scores in the headline, by striking them through. For instance:

## Ruby, <s>104</s> <s>101</s> 96 bytes

If there you want to include multiple numbers in your header (e.g. because your score is the sum of two files or you want to list interpreter flag penalties separately), make sure that the actual score is the last number in the header:

## Perl, 43 + 2 (-p flag) = 45 bytes

You can also make the language name a link which will then show up in the snippet:

## [><>](http://esolangs.org/wiki/Fish), 121 bytes

var QUESTION_ID=67357,OVERRIDE_USER=44713;function answersUrl(e){return"https://api.stackexchange.com/2.2/questions/"+QUESTION_ID+"/answers?page="+e+"&pagesize=100&order=desc&sort=creation&site=codegolf&filter="+ANSWER_FILTER}function commentUrl(e,s){return"https://api.stackexchange.com/2.2/answers/"+s.join(";")+"/comments?page="+e+"&pagesize=100&order=desc&sort=creation&site=codegolf&filter="+COMMENT_FILTER}function getAnswers(){jQuery.ajax({url:answersUrl(answer_page++),method:"get",dataType:"jsonp",crossDomain:!0,success:function(e){answers.push.apply(answers,e.items),answers_hash=[],answer_ids=[],e.items.forEach(function(e){e.comments=[];var s=+e.share_link.match(/\d+/);answer_ids.push(s),answers_hash[s]=e}),e.has_more||(more_answers=!1),comment_page=1,getComments()}})}function getComments(){jQuery.ajax({url:commentUrl(comment_page++,answer_ids),method:"get",dataType:"jsonp",crossDomain:!0,success:function(e){e.items.forEach(function(e){e.owner.user_id===OVERRIDE_USER&&answers_hash[e.post_id].comments.push(e)}),e.has_more?getComments():more_answers?getAnswers():process()}})}function getAuthorName(e){return e.owner.display_name}function process(){var e=[];answers.forEach(function(s){var r=s.body;s.comments.forEach(function(e){OVERRIDE_REG.test(e.body)&&(r="<h1>"+e.body.replace(OVERRIDE_REG,"")+"</h1>")});var a=r.match(SCORE_REG);a&&e.push({user:getAuthorName(s),size:+a[2],language:a[1],link:s.share_link})}),e.sort(function(e,s){var r=e.size,a=s.size;return r-a});var s={},r=1,a=null,n=1;e.forEach(function(e){e.size!=a&&(n=r),a=e.size,++r;var t=jQuery("#answer-template").html();t=t.replace("{{PLACE}}",n+".").replace("{{NAME}}",e.user).replace("{{LANGUAGE}}",e.language).replace("{{SIZE}}",e.size).replace("{{LINK}}",e.link),t=jQuery(t),jQuery("#answers").append(t);var o=e.language;/<a/.test(o)&&(o=jQuery(o).text()),s[o]=s[o]||{lang:e.language,user:e.user,size:e.size,link:e.link}});var t=[];for(var o in s)s.hasOwnProperty(o)&&t.push(s[o]);t.sort(function(e,s){return e.lang>s.lang?1:e.lang<s.lang?-1:0});for(var c=0;c<t.length;++c){var i=jQuery("#language-template").html(),o=t[c];i=i.replace("{{LANGUAGE}}",o.lang).replace("{{NAME}}",o.user).replace("{{SIZE}}",o.size).replace("{{LINK}}",o.link),i=jQuery(i),jQuery("#languages").append(i)}}var ANSWER_FILTER="!t)IWYnsLAZle2tQ3KqrVveCRJfxcRLe",COMMENT_FILTER="!)Q2B_A2kjfAiU78X(md6BoYk",answers=[],answers_hash,answer_ids,answer_page=1,more_answers=!0,comment_page;getAnswers();var SCORE_REG=/<h\d>\s*([^\n,]*[^\s,]),.*?(\d+)(?=[^\n\d<>]*(?:<(?:s>[^\n<>]*<\/s>|[^\n<>]+>)[^\n\d<>]*)*<\/h\d>)/,OVERRIDE_REG=/^Override\s*header:\s*/i;

body{text-align:left!important}#answer-list,#language-list{padding:10px;width:290px;float:left}table thead{font-weight:700}table td{padding:5px}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <link rel="stylesheet" type="text/css" href="//cdn.sstatic.net/codegolf/all.css?v=83c949450c8b"> <div id="answer-list"> <h2>Leaderboard</h2> <table class="answer-list"> <thead> <tr><td></td><td>Author</td><td>Language</td><td>Size</td></tr></thead> <tbody id="answers"> </tbody> </table> </div><div id="language-list"> <h2>Winners by Language</h2> <table class="language-list"> <thead> <tr><td>Language</td><td>User</td><td>Score</td></tr></thead> <tbody id="languages"> </tbody> </table> </div><table style="display: none"> <tbody id="answer-template"> <tr><td>{{PLACE}}</td><td>{{NAME}}</td><td>{{LANGUAGE}}</td><td>{{SIZE}}</td><td><a href="{{LINK}}">Link</a></td></tr></tbody> </table> <table style="display: none"> <tbody id="language-template"> <tr><td>{{LANGUAGE}}</td><td>{{NAME}}</td><td>{{SIZE}}</td><td><a href="{{LINK}}">Link</a></td></tr></tbody> </table>

Answer 1

TeaScript, 5 bytes

xN(0)

TeaScript has a (almost) built-in for this :D

Try it online (note: the online interpreter has been updated to TeaScript v3 so in which this is N0)

Try all the test cases

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TeaScript 3, 2 bytes [non-competing]

Using TeaScript 3, this can become 2-bytes. This is non-competing because TeaScript 3 was made after this challenge

N0

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1 byte alternative

If we could output 0123456789 for digits, then this could be:

°

Answer 2

Pyth, 10 bytes

h/#z[GrG1z

Test suite

We start by constructing a list with 3 elements: the lowercase alphabet, the uppercase alphabet, and the input. ([GrG1z) Then, we filter this list on the number of appearances of the input in the elements being nonzero. (/#z) Finally, we take the first element of the filtered list.

Answer 3

LabVIEW, 23 LabVIEW Primitives

The selector (the ? on the cse structure) is connected to a vi that is called Lexical Class. It ouputs numbers from 1-6 depending on input, 5 is lower case 4 is upper case.

The for loop goes 26 times to create an alphabet or once to pass the symbol through.

Answer 4

Haskell, 48 bytes

f c=filter(elem c)[['a'..'z'],['A'..'Z'],[c]]!!0

Usage example:

*Main> f 'g'
"abcdefghijklmnopqrstuvwxyz"
*Main> f 'H'
"ABCDEFGHIJKLMNOPQRSTUVWXYZ"
*Main> f '\''
"'"

Take all lists of ['a'..'z'], ['A'..'Z'] and the singleton list with the input char c where c is element of. For letters we have always two matches, so we pick the first one.

Answer 5

JavaScript (ES6), 79 bytes

x=>(a="abcdefghijklmnopqrstuvwxyz",x>"`"&x<"{"?a:x>"@"&x<"["?a.toUpperCase():x)

Explanation

JavaScript compares the code of each character alphabetically when comparing strings, so the codes of the characters used in the comparisons are 1 below and above the required range of characters.

x=>(
  a="abcdefghijklmnopqrstuvwxyz", // a = lower-case alphabet
  x>"`"&x<"{"?a:                  // if x is a lower-case letter, output alphabet
  x>"@"&x<"["?a.toUpperCase():    // if x is an upper-case letter, output upper-case
  x                               // else just output x
)

Test

var solution = x=>(a="abcdefghijklmnopqrstuvwxyz",x>"`"&x<"{"?a:x>"@"&x<"["?a.toUpperCase():x)

X = <input type="text" oninput="result.textContent=solution(this.value)" />
<pre id="result"></pre>

Answer 6

R, 90 75 bytes

a=scan(,'');l=letters;L=LETTERS;cat("if"(a%in%l,l,"if"(a%in%L,L,a)),sep="")

Thanks to Giuseppe.

Old version (90 bytes):

a=scan(,'');l=letters;L=LETTERS;if(a%in%l)cat(l,sep="")else if(a%in%L)cat(L,sep="")else a

Looks ugly, but those cats cannot be outsourced to functions, IMHO.

Answer 7

Python 3, 92 84 82 74 bytes

Current version: 74, thanks to isaacg and wnnmaw!

lambda c:(c,''.join(chr(x+(67,97)[c>'Z'])for x in range(25)))[c.isalpha()]

Ungolfed: (for some definition of ungolfed

lambda c:
    (
        c,
        ''.join([chr(x + (67,97)[c > 'Z']) for x in range(25)])
    )
    [c.isalpha()]

---

First version: 92

def f(c):print(''.join([chr(x+(97if c>'Z'else 65)) for x in range(25)])if c.isalpha()else c)

Second version: 82, thanks to isaacg! :)

lambda c:''.join(chr(x+(97if c>'Z'else 65))for x in range(25))if c.isalpha()else c

Answer 8

Python 3, 118 105 98 97 83 bytes

Simple solution. EDIT: Golfed with thanks to Erik the Golfer's suggestion.

lambda s,a='ABCDEFGHIJKLMNOPQRSTUVWXYZ':(s,(a,a.lower())[s.islower()])[s.isalpha()]

Ungolfed:

def f(s):
 a='ABCDEFGHIJKLMNOPQRSTUVWXYZ'
 if s.isalpha():
  if s.islower():return a.lower()
  else:return a
 return s

Answer 9

PHP, 62 76 82 bytes

PHP is doing OK now:

<?=ctype_alpha($x=$argv[1])?join(range(Z<$x?a:A,Z<$x?z:Z)):$x;

Takes an input from command line, like:

$ php alphabet.php A
$ php alphabet.php "a"
$ php alphabet.php " "
$ php alphabet.php _

Edits

• Saved 6 bytes by replacing 91>ord($x) with Z<$x. Thought way to complicated. Thanks to manatwork.
• Saved 14 bytes by removing strtoupper and building the demanded range directly.

Answer 10

Perl, 46 34 33 bytes

includes +2 for -nE

say/[a-z]/?a..z:/[A-Z]/?A..Z:$_

Run as

perl -nE 'say/[a-z]/?a..z:/[A-Z]/?A..Z:$_'

---

• update 34 save 12 bytes by omitting for and using barewords, thanks to @Dom Hastings.
• update 33 save 1 byte using -E and say instead of print.

Answer 11

Ruby, 41 + 1 = 42

With switch -p, run

([*?A..?z]*'').scan(/\w+/){$&[$_]&&$_=$&}

This generates the string

ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz

and checks each contiguous block of "word characters", which happen to be just the lowercase and uppercase alphabets and the underscore character. If there were multiple consecutive word characters between Z and a, this trick wouldn't work.

Edited to add explanation, by request:

The -p flag does essentially

while( $_ = STDIN.gets )
  #execute code
  print $_
end

[*?A..?z] is the array of characters between uppercase A and lowercase Z, in ASCII order. That's the uppercase alphabet, some non-letter characters, and the lowercase alphabet. *'' joins the array into a string, so we can call .scan on it. scan will find each match of the regular expression /\w+/, populate the magic variable $& with it, and call the block. Each time the block is iterated, it checks whether the matched string contains $_ and sets the output to that string if so. So if $_ is contained in either the uppercase or lowercase alphabet, it gets modified accordingly, otherwise it's unchanged.

The ungolfed version would look something like

while ($_ = STDIN.gets )
 %w[ABCDEFGHIJKLMNOPQRSTUVWXYZ abcdefghijklmnopqrstuvwxyz].each do |alphabet|
  $_ = alphabet if alphabet.include?($_)
 end
 print $_
end

Answer 12

Ruby, 46 43 characters

(42 characters code + 1 character command line option)

[?a..?z,?A..?Z].map{|r|r===$_&&$_=[*r]*""}

Thanks to:

• Jordan for the === magic (-3 characters)

Sample run:

bash-4.3$ echo -n 'm' | ruby -pe '[?a..?z,?A..?Z].map{|r|r===$_&&$_=[*r]*""}'
abcdefghijklmnopqrstuvwxyz

bash-4.3$ echo -n 'W' | ruby -pe '[?a..?z,?A..?Z].map{|r|r===$_&&$_=[*r]*""}'
ABCDEFGHIJKLMNOPQRSTUVWXYZ

bash-4.3$ echo -n '@' | ruby -pe '[?a..?z,?A..?Z].map{|r|r===$_&&$_=[*r]*""}'
@

Answer 13

CJam, 18 bytes

'[,65>_elr:R]{R&}=

'[,65> pushes the uppercase alphabet, _el the lowercase alphabet, and r:R a single-char string that is read from STDIN and assigned to variable R. These are wrapped in an array (]) and the first one that has any chars in common with R is selected using {R&}=.

Answer 14

Retina, 62 bytes

[a-z]
abcdefghijklmnopqrstuvwxyz
[A-Z]
ABCDEFGHIJKLMNOPQRSTUVWXYZ

The two short lines are the regex to match. If the input is lowercase (in the range [a-z]), it replaces that character (in this case, that is the entire input) with the lowercase alphabet. The process is similar for uppercase. If it's not a letter, no replacements are made, and it is outputted untouched.

Try it online.

Answer 15

MATL, 22 bytes

jtt1Y2XIm~Iw?km?Ik]]1$

This uses the current version (3.1.0) of the language.

EDIT (Sep 15, 2017): Try it at MATL Online! (with a newer version of the language).

Examples

>> matl jtt1Y2XIm~Iw?km?Ik]]1$
> e
abcdefghijklmnopqrstuvwxyz

>> matl jtt1Y2XIm~Iw?km?Ik]]1$
> T
ABCDEFGHIJKLMNOPQRSTUVWXYZ

>> matl jtt1Y2XIm~Iw?km?Ik]]1$
> "
"

Explanation

j              % input string (assumed to be a single character)        
tt             % duplicate twice
1Y2            % predefined literal: uppercase letters
XI             % copy to clipboard I         
m~             % check if not member    
I              % paste from clipboard I      
w              % swap elements in stack      
?              % if
    k          % convert string to lowercase 
    m          % check if member         
    ?          % if                          
        I      % paste from clipboard I      
        k      % convert string to lowercase 
    ]          % end                         
]              % end                         
1$             % input specification for implicit printing

Answer 16

Python 2.7.10, 95 93 79 bytes

This is my first time even attempting to golf, so please, any help or advice is extremely appreciated!

from string import* 
lambda i:(i,(uppercase,lowercase)[i.islower()])[i.isalpha()]

Thanks to Morgan Thrapp for the help!

Answer 17

Lua, 98 97 bytes

Sadly, I didn't find a solution shorter than 26 bytes to set a with the alphabet. In fact, I didn't find shorter than 32.

Edit : save 1 Byte thanks to @ATaco, was doing this error a lot when started with Lua :p

c=io.read()a="abcdefghijklmnopqrstuvwyz"print(not c:find"%a"and c or c:find"%u"and a:upper()or a)

You can test it online on the official site or on ideone. If you use the former, the input won't work (disabled), so use the following source, where it is wrapped into a function.

function f(c)
  a="abcdefghijklmnopqrstuvwyz"
  print(not c:find"%a"and c or c:find"%u"and a:upper()or a)
end

print(f("\""))
print(f("a"))
print(f("Q"))

Answer 18

Java, 165 characters

class A {public static void main(String[]p){int c=p[0].charAt(0),d=c|32,b=(d-96)*(d-123),e=b<0?65|(c&32):c,f=e+(b<0?26:1);for(;e<f;e++){System.out.print((char)e);}}}

Generates the required output to stdout (rather than returning it). Input is via the runtime arguments.

How it works.

1) Setup some integer variables
c = the ASCII value of the first character of the first parameter of the runtime arguments.
d = c converted to lowercase ASCII value (by ORing it with 32)
b = calculation to see if d is a letter. Will be <0 if a letter.
e = The start character for output. If ASCII value in d is a letter (see b) then it is set to 'A' (or 'a' by adding c AND 32 to 'A' ASCII value) else it is set to the original value of c.
f = the number of characters to output. If it not a letter (see b) then this is set to 1 else it is set to 26
2) Loop from e to e+f outputing each character to stdout.

Answer 19

Perl, 23 bytes

Includes +2 for -nE (instead of the normal +1) to be fair to the other perl solution

Run with the input on STDIN without trailing newline:

echo -n g | perl -lnE 'say/\pL/?a&$_|A..Z:$_'

Just the code:

say/\pL/?a&$_|A..Z:$_

Answer 20

05AB1E, 19 16 bytes

-3 bytes thanks to else

DAsåiAëDAusåiAuë

How it works

                   # implicit input
D                  # duplicate
 A                 # push lowercase alphabet
  s                # swap last two elements
   å               # push a in b
    i              # if
     A             # lowercase alphabet
      ë            # else
         D         # duplicate
          Au       # uppercase alphabet
            s      # swap last two elements
             å     # push a in b
              I    # if
               Au  # uppercase alphabet
                 ë # else leave input
                   # implicit print

Try it online!

Answer 21

Java SE 8, 71 69 bytes

Golfed:

(a,s)->{char b=97;if(a<91)b-=32;a=b;b+=26;while(a<b)s+=a++;return s;}

Ungolfed:

(a,s)->{          // String as a parameter. If declaration is necessary it adds 8 bytes
char b = 97;      // Uppercase A char, this is important
if (a < 91)       // If it is not past 'z', where a is a char param
    b -= 32;      // Then go back to the lowercase alphabet
a = b;            // Done to prevent a cast
b += 26;          // End of alphabet
while (a < b)     // Go to end of alphabet
    s += a++;     // Append character
return s;}        // Then return

I had originally implemented the following

String s="";char b=96;if(a-91<0)b-=32;for(char c=b;++c<b+27;)s+=c;return s;

It's more elegant but sadly it's one byte larger. This is assuming that behavior for non alpha characters is undefined and string s is initialized to "" prior to execution. Be gentle it's my first post.

edit: 2 bytes saved by Stewie Griffin by changing

a - 91 < 0 to a < 91

Answer 22

Scala, 91 characters

(c:Char)=>{var a='a'.to('z').mkString;if(c.isUpper)a=a.toUpperCase;if(!c.isLetter)a=""+c;a}

Un-golfed

def f(c: Char): String = {
    var a='a'.to('z').mkString //set up lower case default response
    if (c.isUpper) {
        a = a.toUpperCase     //mutate the result if upper case
    }        
    if (!c.isLetter) { 
      a = ""+c                 //mutate the result if not a letter
    }
    a                         //return result
}

Having a initial mutable result rather than returning an immutable value from 3 distinct if else blocks saved me 2 chars, even though I hate it.

Scala-thonic method

A better method for scala would be something like this:

def convertToAlphabet(c: Char): String = {
    c match {
      case x if !x.isLetter => x.toString
      case x if x.isUpper => ('A' to 'Z').mkString
      case _ => ('a' to 'z').mkString
    }
}

Answer 23

Japt, 9 bytes

;[CBU]æøU

Run it online

Answer 24

Brachylog, 8 bytes

∈Ạ|ḷ∈Ạụ|

Try it online!

∈Ạ          The input is a member of the lowercase alphabet,
  |         which is output, or
   ḷ∈Ạ      the input lowercased is a member of the lowercase alphabet,
      ụ|    which is output uppercased, or the input is output.

It'd be two bytes shorter if we had a constant for the uppercase alphabet but we don't :(

Answer 25

SpecBAS, 111 bytes

I've been through several versions of this, 111 seems to be the best I can manage.

1 INPUT l$: a$="abcdefghijklmnopqrstuvwxyz"
2  ?IIF$(l$ IN ["a" TO "z","A" TO "Z"],IIF$(l$=UP$ l$,UP$ a$,a$),l$)

Line 2 uses the ? shortcut for PRINT and nested inline IF statements

Pseudo code explanation

IF character IN "a".."z","A".."Z"
THEN
 IF character = UPPERCASE character
 THEN
  print UPPERCASE alphabet
 ELSE
  print alphabet
 ENDIF
ELSE
 print the character
ENDIF

Answer 26

Mathematica, 75 bytes

#/.Thread[Join[a=Alphabet[],b=ToUpperCase@a]->Array[""<>If[#>26,b,a]&,52]]&

Pretty good score for a non-golfing language... Any solutions using character code processing would take more bytes, due to the costs of ToCharacterCode and FromCharacterCode.

Answer 27

Python, 81 bytes

f=lambda z,a="abcdefghijklmnopqrstuvwxyz":[k for k in[a,a.upper(),z]if z in k][0]

This is basically a translation of the Pyth answer. It defines a function f that takes as argument the character and returns the result.

Answer 28

MATLAB: 71 68 bytes

i=input('');b=i<65|i>122|(i>90&i<97);[i*b,~b*((65:90)+32*(i>96)),'']

(thanks to OP for saving 3 bytes)

Test:

i='a'
ans=
abcdefghijklmnopqrstuvwxyz

i='A'
ans=
ABCDEFGHIJKLMNOPQRSTUVWXYZ

i='~'
ans=
~

Explanation: Uppercase alphabet occupies 65:90 ASCII characters. Lowercase alphabet is at 97:122 ASCII. So, b=i<65|i>122|(i>90&i<97) checks whether the input character i is NOT alphabetic. If so, input is returned. The uppercase alphabet is returned if b==1 and i<97 (uppercase character). If b==1 and i>96, 32 is added to 65:90 that corresponds to 97:122 - the lowercase alphabet.

Answer 29

Swift 2, 142 Bytes

func d(s:String)->String{let a="abcdefghijklmnopqrstuvwxyz";for v in s.utf8{return v>64&&v<91 ?a.uppercaseString:(v>96&&v<123 ?a:s)};return s}

Ungolfed

func d(s: String) -> String{
    let a="abcdefghijklmnopqrstuvwxyz"
    for v in s.utf8{
        return (
            v > 64 && v < 91 ?
            a.uppercaseString :
            (
                v > 96 && v < 123 ?
                a :
                s
            )
        )
     }
    return s
}

Answer 30

C (function), 71 bytes

f(s,n,c){n=1;if(isalpha(s))s-=s%32-1,n=26;for(c=s;c<s+n;)putchar(c++);}

Answer 31

Jolf, 17 bytes

Try it here.

? hpLipl? hpUipui
?                  if
  hpL               the lowercase alphabet (array) contains
     i               the input
      pl            return the lowercase alphabet (string)
        ?          else if
          hpU       the uppercase alphabet (array) contains
             i       the input
              pu    return the uppercase alphabet (string)
                i  otherwise, return the input
                   implicit: print the result

Answer 32

Perl 6, 50

{join "",/<:Lu>/??"A".."Z"!!/<:Ll>/??"a".."z"!!$_}

Answer 33

PHP, 60 bytes

for(ctype_alpha($c=$argn)?$c=$c&a|A:$z=25;$z++<26;)echo$c++;

Run as pipe with -R.

Answer 34

Recursiva, 13 bytes

||&N(a(&N)a)a

Try it online!

Explanation:

This roughly translates to 'N(a and (' or 'N)a and )' or a. N(a checks if a is in (. ( and ) are upper and lower-case alphabet yield.

Answer 35

Ly, 32 bytes

"AZ"Ris~[p&o;]&p"az"Rl~[p&o;]lo;

Try it online!

Explanation:

"AZ"Ris~[p&o;]&p"az"Rl~[p&o;]lo;

     is                          # take input and save it
"AZ"R  ~[    ]                   # is it in the uppercase alphabet?
         p&o;                    # output the stack, terminate
              &p                 # clear stack
                     l           # load input
                "az"R ~[    ]    # is it in the lowercase alphabet?
                        p&o;     # output the stack, terminate
                             lo; # output the input, terminate

Answer 36

Python 2, 73 bytes

c=ord(input())
print[chr(c),bytearray(range(c&96|1,c&96|27))][64<c&95<91]

Try it online!

Answer 37

APL (Dyalog Unicode), 26 24 bytes

t←{⍵∊g←819⌶f←⎕A:g⋄⍵∊f:f⋄⍵}

Try it online!

The byte count does not include t← because it's not necessary, it just assigns the function to t (so you can call it by using t input).

If input is not a number, it needs to be enclosed in single quotes. For the input ', you need to escape it by typing it twice (so the call is t '''')

Thanks to @Adám for 2 bytes.

How it works:

{⍵∊g←819⌶f←⎕A:g⋄⍵∊f:f⋄⍵} ⍝ Main function
             :            ⍝ if
         f←⎕A             ⍝ Assigns the uppercase alphabet to f
   g←819⌶                 ⍝ Assigns the I-Beam command 819 (case convert) over the uppercase alphabet (f) to g
 ⍵∊                       ⍝ The right argument 'is in' the lowercase alphabet
              g           ⍝ then print g (the lowercase alphabet)
               ⋄   :      ⍝ else if
                ⍵∊f       ⍝ the right argument 'is in' f (the uppercase alphabet)           
                    f     ⍝ print f
                     ⋄⍵   ⍝ else, print the right argument.

Answer 38

APL (Dyalog), 22 bytes

Unnamed prefix lambda.

{⊃a/⍨⍵∊¨a←⎕A(819⌶⎕A)⍵}

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{…} anonymous function where ⍵ represents the argument:

 ⎕A(819⌶⎕A)⍵ uppercase Alphabet, lowercased Alphabet, argument

 a← store in a (for all)

 ⍵∊¨ three Booleans for argument's membership of each those

 a/⍨ filter a by that

 ⊃ pick the first

Answer 39

C (gcc), 94 bytes

#define f(c)isupper(c)?"ABCDEFGHIJKLMNOPQRSTUVWXYZ":islower(c)?"abcdefghijklmnopqrstuvwxyz":&c

#define f(c) is like declaring a function f that takes a variable c.

isupper(c) checks if c is an uppercase letter, returns the uppercase alphabet if so. Otherwise, it checks if it's lowercase. If so, it returns the lowercase alphabet. Otherwise, it returns a pointer to c, which can be printed as a string (since you must pass a char or int to f).

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Answer 40

R, 80 bytes

s=(r=65:90)+32
a=utf8ToInt(scan(,''));intToUtf8("if"(a%in%r,r,"if"(a%in%s,s,a)))

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-1 byte thanks to Giuseppe. Still not the golfiest way (see here). Similar ideas include:

R, 87 bytes

f=function(x,y)"if"(a%in%x,x,y)
a=utf8ToInt(scan(,''));intToUtf8(f(r<-65:90,f(r+32,a)))

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a=utf8ToInt(scan(,''));intToUtf8("if"(a%in%c(32:64,91:96,123:126),a,65:90+32*(a>90)))

and my favorite:

a=utf8ToInt(scan(,''));intToUtf8(c(a,65:90+32*(a>90))[2*a%in%c(32:64,91:96,123:126)-1])

and inspired by the other R solution (same bytecount):

"+"=function(x,y)"if"(a%in%x,x,y)
a=scan(,'');cat(letters+LETTERS+a,sep="")

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Answer 41

Noether, 40 bytes

{0A~bI~a/~c}{bP}b{Ua/~d}{bUP}1{cd|-}{aP}

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Uses Noether's built-in constant function A to return the string abcdefghijklmnopqrstuvwxyx.

Answer 42

C# .NET, 193 bytes

class P{static void Main(string[]a){var z="ABCDEFGHIJKLMNOPQRSTUVWXYZ";var b=a[0];System.Console.Write(b.Length>1?b:z.IndexOf((b[0]))>-1?z:z.ToLower().IndexOf((b[0]))>-1?z.ToLower():b[0]+"");}}

Try Online EDIT: Variable assignment with if statements is stupid

Answer 43

Keg, -ir 45 37 21 bytes

:AZ"•[_AZɧ|:az"•[_azɧ

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-16 bytes due to using ranges

Answer History

37 bytes

::`>$\~<*[_z(|:;)^|:A1->[_Z(|:;)^|,

-8 bytes thanks to A__

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Answer 44

Zsh, 75 bytes

l=${(j::):-{a..z}} u=$l:u
<<<${${${l:#*$1*}:+${${${u:#*$1*}:+$1}:-$u}}:-$l}

---

l=${(j::):-{a..z}}                                  # set l to the (j::)oined lowercase
                   u=$l:u                           # set u to :uppercase'd l
<<<${${${l:#*$1*}:+${${${u:#*$1*}:+$1}:-$u}}:-$l}
       ${l:#*$1*}                                   # remove *$1* from $l (is empty if $1 is lower)
     ${          :+                        }        # If non-empty, then...
                       ${u:#*$1*}                   # remove *$1* from $u (is empty if $1 is upper)
                     ${          :+$1}              # If non-empty, substitute $1
                   ${                 :-$u}         # If empty, substitute $u
    ${                                       :-$l}  # If empty, substitute $l

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Answer 45

Python 3, 84 bytes

lambda x,a='abcdefghijklmnopqrstuvwxyz':[x,a,a.upper()][(x in a)+2*(x in a.upper())]

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Answer 46

Wolfram Language (Mathematica), 62 bytes

""<>(#/.Join[a=Alphabet[];A=ToUpperCase@a;#->a&/@a,#->A&/@A])&

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Answer 47

Python 3, 93 bytes

i=input();a="abcdefghijklmnopqrstuvwxyz";A=a.upper();print(i in a and a or i in A and A or i)

Under 100 bytes!

Answer 48

Gema, 60 characters

\A=@set{a;abcdefghijklmnopqrstuvwxyz}
<J>=$a
<K>=@upcase{$a}

Sample run:

bash-4.3$ gema '\A=@set{a;abcdefghijklmnopqrstuvwxyz};<J>=$a;<K>=@upcase{$a}' <<< 'm'
abcdefghijklmnopqrstuvwxyz

bash-4.3$ gema '\A=@set{a;abcdefghijklmnopqrstuvwxyz};<J>=$a;<K>=@upcase{$a}' <<< 'W'
ABCDEFGHIJKLMNOPQRSTUVWXYZ

bash-4.3$ gema '\A=@set{a;abcdefghijklmnopqrstuvwxyz};<J>=$a;<K>=@upcase{$a}' <<< '@'
@

Answer 49

Seriously, 17 bytes

    ;;ú(úíuIúû;(@íuI

Hex Dump:

093b3ba328a3a17549a3963b2840a17549

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Given that it pretty much just reads in an unformatted byte, checks if it's in the lowercase alphabet, then checks if it's in the uppercase alphabet, the automatic documentation given in the link is sufficient. (Note, however, that the documentation for í has the argument order reversed; it pops the sequence first.)

Answer 50

Python 2, 67 bytes

f=lambda c,i=26:c[c.isalpha():]or c*i and f(c,i-1)+chr(i^ord(c)&96)

For letter inputs, generates the string of letters recursively. Doing ord(c)&96 removes the 5 high bits, and the xor'ing the values i from 1 to 26 gives the letter char codes. For control flow, we count i down, adding new letters to the end, stopping when i=0. When the input c is not a letter, immediately outputs it and stops.

Thanks to Mauris for 2 bytes.

Previous solution (68):

lambda c:[c,str(bytearray(range(ord(c)&96,255)[1:27]))][c.isalpha()]

Answer 51

Sed, 61 characters

(60 characters code + 1 character command line option)

s/[a-z]/&abcdefghijklmnopqrstuvwxyz/i
s/[A-Z].*/\U&/
T
s/.//

Sample run:

bash-4.3$ sed -r 's/[a-z]/&abcdefghijklmnopqrstuvwxyz/i;s/[A-Z].*/\U&/;T;s/.//' <<< 'm'
abcdefghijklmnopqrstuvwxyz

bash-4.3$ sed -r 's/[a-z]/&abcdefghijklmnopqrstuvwxyz/i;s/[A-Z].*/\U&/;T;s/.//' <<< 'W'
ABCDEFGHIJKLMNOPQRSTUVWXYZ

bash-4.3$ sed -r 's/[a-z]/&abcdefghijklmnopqrstuvwxyz/i;s/[A-Z].*/\U&/;T;s/.//' <<< '@'
@

Answer 52

Python 2.7, 88 bytes (incl. print)

from string import*
def f(c):print[c,uppercase,c,lowercase,c][sorted('@Z`z'+c).index(c)]

Answer 53

JavaScript (ES6), 99 87 79 78 bytes

x=>(y='abcdefghijklmnopqrstuvwxyz',parseInt(x,36)>9?x>'`'?y:y.toUpperCase():x)

Uses the short array fill trick to allocate space, then just math and String.fromCharCode to get the alphabet. Thought it would be shorter until I realized the rule about non-alphabet characters. parseInt turned out to be helpful in determining if the character was in the alphabet.

Test

var F=x=>(y='abcdefghijklmnopqrstuvwxyz',parseInt(x,36)>9?x>'`'?y:y.toUpperCase():x)

x = <input type="text" oninput="result.textContent=this.value?F(this.value):''" />
<pre id="result"></pre>

Answer 54

Mouse-2002, 125 bytes

... or 126 bytes if I can't assume a REPL envrironment (which assumes a $ at the end of the program; the non-REPL interpreter crashes without one)

An attempt at code deduplication... probably a failed one.

Golfed:

?'a:123b:a.65<a.31>*1=a.90>a.97<*1=+a.122>+1=[a.!']a.63>a.91<*1=[65i:(i.91<^i.!'i.1+i:)]a.96>a.b.<*1=[97i:(i.b.<^i.!'i.1+i:)]

Ungolfed:

?' a:                    ~ a = getchar();
123 b:                   ~ b = 123
a. 65 <                  ~ return whether a < 65
a. 31 >                  ~ same for 31
  * 1 =                    ~ AND
a. 90 >                  ~ a > 90 ?
a. 97 <                  ~ a < 97 ?
  * 1 =                    ~ AND
+                          ~ OR
a.122 >                  ~ a > 122 ?
  + 1 =                    ~ OR
[                          ~ if 1
  a.!'                       ~ print ascii codepoint
]                          ~ fi
a. 63 >                  ~ a > 63 ?
a. 91 <                  ~ a < 91 ?
  * 1 =                    ~ AND
[                          ~ if 1
  65 i:                      ~ for i = 65;
  (                          ~ do;
    i. 91 < ^                  ~ i < 91;
    i.!'                       ~ print(charAt(i));
    i. 1+ i:                   ~ i++;
  )                         ~ done;
]                          ~ fi
a. 96 >                  ~ a > 96 ?
a. b. <                  ~ a < b ?
  * 1 =                    ~ AND
[                          ~ if 1
  97 i:                      ~ for i = 97;
  (                          ~ do;
    i. b. < ^                  ~ i < 91; 
    i.!'                       ~ print(charAt(i));
    i. 1+ i:                   ~ i++;
  )                          ~ done;
]                          ~ fi
$                        ~ \bye

Answer 55

Ruby, 56+2 = 58 bytes

2 bytes for -p flag

c=$_[0]
[?a..?z,?A..?Z].map{|r|r===c&&c=r.to_a.join}
p c

Ungolfed version (no -p flag)

while true
  char = gets.chars.first
  [("a".."z"),("A".."Z")].each do |range|
    char = range.to_a.join("") if range.include? char
  end
  p char
end

Answer 56

s-lang, 40 bytes (non-competing)

Replaces any letter with the alphabet, matching the case.

t@[[a-z]][abcdefghijklmnopqrstuvwxyz]

• t Replace with regex function
• @ Match case for entire match parameter for t function
• [[a-z]] first argument ([a-z]) regex for matching any letter (@ parameter makes it so this function ignores the case when matching, so we don't need A-Z too)
• abcdefghijklmnopqrstuvwxyz what to replace it with

Try it here

Answer 57

Java 7, 99 bytes

void f(char c){for(int a=c|32,i=97;i<123;i++)System.out.print(a<123&a>96?(char)(i-a+c):i<98?c:"");}

Slightly more readable, with no scrollbars:

void f(char c){
    for(int a=c|32,i=97;i<123;i++)  // a is lowercased input, i loops alphabet 
        System.out.print(           
            a<123&a>96?             // if a is a letter
                (char)(i-a+c):      //   subtract diff between lower and input
                    i<98?c:"");     // else print input if first iteration
}

The logic here is pretty straightforward, but a different method than the other Java answer.

Answer 58

AWK 104 bytes

/[a-z]/{print"abcdefghijklmnopqrstuvwxyz"}
/[A-Z]/{print"ABCDEFGHIJKLMNOPQRSTUVWXYZ"}
/[^A-z]/{print$0}

Answer 59

Powershell, 116 bytes

$b='j';$a='ABCDEFGHIJKLMNOPQRSTUVWXYZ';switch($b){{$b-cmatch'[a-z]'}{$a.ToLower()}{$b-cmatch'[A-Z]'}{$a}default{$_}}

Change $b='j' to modify result.

I couldn't figure out a way to get the alphabet that was shorter than just writing the alphabet unfortunately.

e.g. (65..90|%{[char][byte]$_})-join''

Answer 60

Excel VBA, 114 Bytes

Anonymous VBE immediate window function that takes input and outputs to the VBE immediate window.

a=Asc([A1]):i=IIf(a>64And a<91,64,(a>96And a<123)*-96):?IIf(i=0,[A1],"");:If i>0 Then For j=1To 26:?Chr(i+j);:Next

Answer 61

REXX, 75 bytes

b=arg(1)
a=xrange(a,z)
if b>z then a=lower(a)
if verify(b,a) then a=b
say a

Answer 62

Jelly, 11 bytes

XØA,Øa¤ċÐfȯ

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Answer 63

Ink, 103 bytes

VAR u="ABCDEFGHIJKLMNOPQRSTUVWXYZ"
VAR l="abcdefghijklmnopqrstuvwxyz"
=o(c)
{u?c:{u}|{l?c:{l}|{c}}}->->

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Answer 64

k4, 24 bytes

{*b@&x in/:b:(.Q`A`a),x}

Another port of the Pyth answer—constructs a list of upper, lower, and the arg, and returns the first one that contains the arg.

Answer 65

Sprects, 207 bytes

|<CHAR>|ZA|YA|XA|WA|VA|UA|TA|SA|RA|QA|PA|OA|NA|MA|LA|KA|JA|IA|HA|GA|FA|EA|DA|CA|BA|AABCDEFGHIJKLMNOPQRSTUVWXYZ|za|ya|xa|wa|va|ua|ta|sa|ra|qa|pa|oa|na|ma|la|ka|ja|ia|ha|ga|fa|ea|da|ca|ba|aabcdefghijklmnopqrstuvwxyz

Enter character on <CHAR>.