Case-sensitivity of identifiers: Difference between revisions

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Three dogs (Are there three dogs or one dog?) is a code snipped used to illustrate the lettercase sensitivity of the programming language. For a case sensitive language, the identifiers dog, Dog and DOG are all different and we should get the output:

The three dogs are named Benjamin, Samba and Bernie.

For a language that is lettercase insensitive, we get the following output:

There is just one dog named Bernie.

Ada

case insensitive <lang Ada>with Ada.Text_IO; procedure Dogs is

  Dog : String := "Bernie";

begin

  Ada.Text_IO.Put_Line ("There is just one dog named " & DOG);

end Dogs;</lang>

Output:

There is just one dog named Bernie

AWK

<lang awk>BEGIN { dog = "Benjamin" Dog = "Samba" DOG = "Bernie" printf "The three dogs are named %s, %s and %s.\n", dog, Dog, DOG }</lang>

The three dogs are named Benjamin, Samba and Bernie.

bc

The only variables are 'a' through 'z'. They can only hold numbers, not strings. Some implementations allow longer names like 'dog', but only with lowercase letters. A name like 'Dog' or 'DOG' is a syntax error.

<lang bc>obase = 16 ibase = 16

/*

* Store the hexadecimal number 'BE27A312'
* in the variable 'd'.
*/

d = BE27A312 "There is just one dog named "; d quit</lang>

There is just one dog named BE27A312

C

C is case sensitive; if it would be case insensitive, an error about redefinition of a variable would be raised.

<lang c>#include <stdio.h>

static const char *dog = "Benjamin"; static const char *Dog = "Samba"; static const char *DOG = "Bernie";

int main() {

   printf("The three dogs are named %s, %s and %s.\n", dog, Dog, DOG);
   return 0;

}</lang>

Common Lisp

<lang lisp>CL-USER> (let* ((dog "Benjamin") (Dog "Samba") (DOG "Bernie")) (format nil "There is just one dog named ~a." dog))

in: LAMBDA NIL
(LET* ((DOG "Benjamin") (DOG "Samba") (DOG "Bernie"))
(FORMAT NIL "There is just one dog named ~a." DOG))

caught STYLE-WARNING
The variable DOG is defined but never used.

caught STYLE-WARNING
The variable DOG is defined but never used.

compilation unit finished
caught 2 STYLE-WARNING conditions

"There is just one dog named Bernie."</lang>

The style warnings come from SBCL.

D

<lang d>import std.stdio;

void main() {

   string dog = "Benjamin";
   string Dog = "Samba";  // identifiers that start with capital letters are type names
   string DOG = "Bernie";
   writefln("There are three dogs named ", dog, ", ", Dog, ", and ", DOG, "'");

}</lang> Output:

There are three dogs named Benjamin, Samba, and Bernie'

dc

A register name has only one character, so this example uses 'd' and 'D'.

<lang dc>[Benjamin]sd [Samba]sD [The two dogs are named ]P ldP [ and ]P lDP [. ]P</lang>

The two dogs are named Benjamin and Samba.

Euphoria

Works with: Euphoria 4.0.0

<lang Euphoria>-- These variables are all different sequence dog = "Benjamin" sequence Dog = "Samba" sequence DOG = "Bernie" printf( 1, "The three dogs are named %s, %s and %s\n", {dog, Dog, DOG} )</lang>

Fortran

Works with: Fortran version 90 and later

Fortran is case insensitive <lang fortran>program Example

 implicit none

 character(8) :: dog, Dog, DOG

 dog = "Benjamin"
 Dog = "Samba"
 DOG = "Bernie"

 if (dog == DOG) then
   write(*,*) "There is just one dog named ", dog
 else
   write(*,*) "The three dogs are named ", dog, Dog, " and ", DOG
 end if

end program Example</lang> Output:

 There is just one dog named Bernie

Go

Go is case sensitive. Further, visibility depends on case. See the Go entry under the Scope modifiers task. <lang go>package dogs

import "fmt"

var dog, Dog, DOG string

func init() {

   dog = "Salt"
   Dog = "Pepper"
   DOG = "Mustard"

}

func PackageSees() () {

   fmt.Println("Package sees:", dog, Dog, DOG)

}</lang> <lang go>package main

import (

   . "dogs"
   "fmt"

)

// with the dogs package imported, there are three dogs, but only two are // visible from here.

func main() {

   // The declaration of dog is required here.  Without it, the Println
   // just below would not compile.  The variable dog in the package is
   // not visible because it begins with a lower case letter.
   dog := "Benjamin"
   // four dogs now.  three visible from here.
   PackageSees()
   fmt.Println("Main sees:   ", dog, Dog, DOG, "\n")

   // Not a declaration, just an assigment.  This assigns a new value to
   // the variable Dog declared in the package.  Dog is visible because
   // it begins with an upper case letter.
   Dog = "Samba"
   // same four dogs, same three visible, one just has a new name.
   PackageSees()
   fmt.Println("Main sees:   ", dog, Dog, DOG, "\n")

   // Of course you can still declare a variable if you want to.  This
   // declares a new variable, shadowing DOG in the package and rendering
   // it inaccessable even though it begins with an upper case letter.
   var DOG = "Bernie"
   // five dogs now.  three visible from here.
   PackageSees()
   fmt.Println("Main sees:   ", dog, Dog, DOG, "\n")

   fmt.Println("There are five dogs.")

}</lang> Output:

Package sees: Salt Pepper Mustard
Main sees:    Benjamin Pepper Mustard 

Package sees: Salt Samba Mustard
Main sees:    Benjamin Samba Mustard 

Package sees: Salt Samba Mustard
Main sees:    Benjamin Samba Bernie 

There are five dogs.

Groovy

Solution: <lang groovy>def dog = "Benjamin", Dog = "Samba", DOG = "Bernie" println (dog == DOG ? "There is one dog named ${dog}" : "There are three dogs named ${dog}, ${Dog} and ${DOG}.")</lang>

Output:

There are three dogs named Benjamin, Samba and Bernie.

Icon and Unicon

The program below demonstrates the three dog task. All variants of Icon/Unicon have case sensitive variable names. But if one wasn't this would find it. <lang Icon>procedure main()

  dog := "Benjamin"
  Dog := "Samba"
  DOG := "Bernie"

  if dog == DOG then 
     write("There is just one dog named ", dog,".") 
  else 
     write("The three dogs are named ", dog, ", ", Dog, " and ", DOG, ".")

end</lang>

J

<lang j> NB. These variables are all different

  dog=: 'Benjamin'
  Dog=: 'Samba'
  DOG=: 'Bernie'
  'The three dogs are named ',dog,', ',Dog,', and ',DOG

The three dogs are named Benjamin, Samba, and Bernie </lang>

Java

<lang java>String dog = "Benjamin"; String Dog = "Samba"; //in general, identifiers that start with capital letters are class names String DOG = "Bernie"; //in general, identifiers in all caps are constants //the conventions listed in comments here are not enforced by the language System.out.println("There are three dogs named " + dog + ", " + Dog + ", and " + DOG + "'");</lang>

K

 dog: "Benjamin"
 Dog: "Samba"
 DOG: "Bernie"
 "There are three dogs named ",dog,", ",Dog," and ",DOG

"There are three dogs named Benjamin, Samba and Bernie" </lang>

Lua

<lang lua>dog = "Benjamin" Dog = "Samba" DOG = "Bernie"

print( "There are three dogs named "..dog..", "..Dog.." and "..DOG.."." )</lang>

There are three dogs named Benjamin, Samba and Bernie.

PARI/GP

<lang parigp>dog="Benjamin"; Dog="Samba"; DOG="Bernie"; printf("The three dogs are named %s, %s, and %s.", dog, Dog, DOG)</lang>

Perl

<lang perl># These variables are all different $dog='Benjamin'; $Dog='Samba'; $DOG='Bernie'; print "The three dogs are named $dog, $Dog, and $DOG \n"</lang>

PicoLisp

<lang PicoLisp>(let (dog "Benjamin" Dog "Samba" DOG "Bernie")

  (prinl "The three dogs are named " dog ", " Dog " and " DOG) )</lang>

Output:

The three dogs are named Benjamin, Samba and Bernie

Prolog

In Prolog, the initial of a variable must be a uppercase letter. So the task can't be completed but we can write this code : <lang Prolog>three_dogs :- DoG = 'Benjamin', Dog = 'Samba', DOG = 'Bernie', format('The three dogs are named ~w, ~w and ~w.~n', [DoG, Dog, DOG]). </lang> The output is :

?- three_dogs.
The three dogs are named Benjamin, Samba and Bernie.
true.

PureBasic

<lang PureBasic>dog$="Benjamin" Dog$="Samba" DOG$="Bernie" Debug "There is just one dog named "+dog$</lang>

Python

Python names are case sensitive: <lang python>>>> dog = 'Benjamin'; Dog = 'Samba'; DOG = 'Bernie' >>> print ('The three dogs are named ',dog,', ',Dog,', and ',DOG) The three dogs are named Benjamin , Samba , and Bernie >>> </lang>

Ruby

Ruby gives a special meaning to the first letter of a name. A lowercase letter starts a local variable. An uppercase letter starts a constant. So dog is a local variable, but Dog and DOG are constants. To adapt this task to Ruby, I added dOg and doG so that I have more than one local variable.

<lang ruby>module FiveDogs

 dog = "Benjamin"
 dOg = "Dogley"
 doG = "Fido"
 Dog = "Samba"   # this constant is FiveDogs::Dog
 DOG = "Bernie"  # this constant is FiveDogs::DOG

 names = [dog, dOg, doG, Dog, DOG]
 names.uniq!
 puts "There are %d dogs named %s." % [names.length, names.join(", ")]
 puts
 puts "The local variables are %s." % local_variables.join(", ")
 puts "The constants are %s." % constants.join(", ")

end</lang>

Output:

There are 5 dogs named Benjamin, Dogley, Fido, Samba, Bernie.

The local variables are dog, dOg, doG, names.
The constants are Dog, DOG.

Sather

Though by convention Sather uses all uppercase letters for class names, a variable can be all uppercase.

<lang sather>class MAIN is

 main is
   dog ::= "Benjamin";
   Dog ::= "Samba";
   DOG ::= "Bernie";
   #OUT + #FMT("The three dogs are %s, %s and %s\n", 
                dog, Dog, DOG);
 end;

end;</lang>

Outputs:

The three dogs are Benjamin, Samba and Bernie

Scheme

<lang scheme>(define dog "Benjamin") (define Dog "Samba") (define DOG "Bernie")

(if (eq? dog DOG)

       (begin (display "There is one dog named ")
               (display DOG)
               (display ".")
               (newline))
       (begin (display "The three dogs are named ")
               (display dog) (display ", ")
               (display Dog) (display " and ")
               (display DOG)
               (display ".")
               (newline)))</lang>

Outputs:

The three dogs are named Benjamin, Samba and Bernie.

Smalltalk

Works with: GNU Smalltalk

Smalltalk's symbols are case sensitive.

<lang smalltalk>|dog Dog DOG| dog := 'Benjamin'. Dog := 'Samba'. DOG := 'Bernie'. ( 'The three dogs are named %1, %2 and %3' %

 { dog . Dog . DOG } ) displayNl.</lang>

Outputs:

The three dogs are named Benjamin, Samba and Bernie

Tcl

Tcl variable names are case sensitive: <lang tcl>set dog "Benjamin" set Dog "Samba" set DOG "Bernie" puts "The three dogs are named $dog, $Dog and $DOG"</lang> Which prints...

The three dogs are named Benjamin, Samba and Bernie

UNIX Shell

<lang bash>dog="Benjamin" Dog="Samba" DOG="Bernie" echo "The three dogs are named $dog, $Dog and $DOG."</lang>

The three dogs are named Benjamin, Samba and Bernie.