Loops/For with a specified step

Loops/For with a specified step
You are encouraged to solve this task according to the task description, using any language you may know.

Demonstrate a for loop where the step value is greater than one.

Ada

The FOR loop construct in Ada does not give the programmer the ability to directly modify the loop control variable during the execution of the loop. Instead, Ada automatically takes care of the modification of the loop control variable by incrementing it or decrementing it to be the next value in a specified discrete sequence. For this reason, in a "real" program, an Ada programmer would use a WHILE loop, or more likely a general LOOP, construct to perform this particular task. For the sake of this task, however, the following code demonstrates a way the task could be performed, when the range of loop control values is sufficiently small, through the definition of an enumeration type.

In the declarative section: <lang ada>type Loop_Steps is (2, 4, 6, 8);</lang> In the body section: <lang ada>for Step in Loop_Steps loop

  put(Step, 0);
  put(", ");

end loop; put("who do we appreciate?");</lang> Another way to do this, which would be more practical for larger ranges, is to loop through all of the values in a range (even the ones we weren't interested in using) and use a conditional check to determine whether or not to use the current loop control variable at each iteration. This is rather inefficient, growing more so as the step values get larger, but it's still order of O(n). Again, this is purely academic, since an actual Ada programmer would rarely do something like this.

The following code prints multiples of three from 3 to 12: <lang ada>for Value in 3 .. 12 loop

  if Value mod 3 = 0 then
     put(Value, 0);
     put(", ")
  end if;

end loop; put("what's a word that rhymes with ""twelve""?");</lang>

ALGOL 68

The ALGOL 68 "universal" for/while loop:

 [ for index ] [ from first ] [ by increment ] [ to last ] [ while condition ] do statements od
 The minimum form of a "loop clause" is thus: do statements od # an infinite loop #

The formal specification of ALGOL 68 states:

for i from u1 by u2 to u3 while condition do action od

"is thus equivalent to the following void-closed-clause:"

begin int f:= u1, int b = u2, t = u3;
   step2:
     if (b > 0 ∧ f ≤ t) ∨ (b < 0 ∧ f ≥ t) ∨ b = 0
     then int i = f;
         if condition
         then action; f +:= b; go to step2
         fi
     fi
end

Note: Highlighting is as per the formal specification, c.f. Category:ALGOL 68#Example of different program representations.

There are several unusual aspects of the construct:

• • only the 'do ~ od' portion was compulsory, in which case the loop will iterate indefinitely.
  • thus the clause 'to 100 do ~ od', will iterate only 100 times.
  • the while "syntactic element" allowed a programmer to break from a for loop early. eg

int sum sq:=0;
for i while
  sum sq ≠ 70 × 70
do
  sum sq +:= i ↑ 2
od 

Subsequent "extensions" to the standard Algol68 allowed the to syntactic element to be replaced with upto and downto to achieve a small optimisation. The same compilers also incorporated:

• until^(C) - for late loop termination.
• foreach^(S) - for working on arrays in parallel.

AutoHotkey

<lang AutoHotkey>SetBatchLines, -1 iterations := 5 step := 10 iterations *= step Loop,  % iterations {

  If Mod(A_Index, step)
     Continue
  MsgBox, % A_Index

} ExitApp</lang>

BASIC

Works with: QuickBasic version 4.5

<lang qbasic>for i = 2 to 8 step 2

  print i; ", ";

next i print "who do we appreciate?"</lang>

C

This prints all odd digits: <lang c>int i; for(i = 1; i < 10; i += 2)

 printf("%d\n", i);</lang>

C++

This prints all odd digits: <lang cpp>for (int i = 1; i < 10; i += 2)

 std::cout << i << std::endl;</lang>

C#

<lang csharp>using System;

class Program {

   static void Main(string[] args) {    
       for (int i = 2; i <= 8; i+= 2) {        
           Console.Write("{0}, ", i);
       }

       Console.WriteLine("who do we appreciate?");
   }

}</lang>

Common Lisp

<lang lisp>(loop for i from 2 to 8 by 2 do

 (format t "~d, " i))

(format t "who do we appreciate?~%")</lang>

D

Print odd numbers up to 9. <lang d>for (int i = 1; i < 10; i += 2)

 std.stdio.writefln("%d\n",i);</lang>

Dao

<lang dao># first value: 1

1. max value: 9
2. step: 2

for( i = 1 : 2 : 9 ) io.writeln( i )</lang>

E

There is no step in the standard numeric range object (a..b and a..!b) in E, which is typically used for numeric iteration. An ordinary while loop can of course be used:

<lang e>var i := 2 while (i <= 8) {

   print(`$i, `)
   i += 2

} println("who do we appreciate?")</lang>

A programmer frequently in need of iteration with an arbitrary step should define an appropriate range object:

<lang e>def stepRange(low, high, step) {

   def range {
       to iterate(f) {
           var i := low
           while (i <= high) {
               f(null, i)
               i += step
           }
       }
   }
   return range

}

for i in stepRange(2, 9, 2) {

 print(`$i, `)

} println("who do we appreciate?")</lang>

The least efficient, but perhaps convenient, solution is to iterate over successive integers and discard undesired ones:

<lang e>for i ? (i %% 2 <=> 0) in 2..8 {

   print(`$i, `)

} println("who do we appreciate?")</lang>

Factor

Prints odd digits. <lang factor>1 10 2 <range> [ . ] each</lang>

FALSE

<lang false>2[$9\>][$.", "2+]#"who do we appreciate!"</lang>

Forth

<lang forth>: test

 9 2 do
   i .
 2 +loop
 ." who do we appreciate?" cr ;</lang>

Fortran

Works with: Fortran version 90 and later

<lang fortran>do i = 1,10,2

  print *, i

end do</lang>

F#

<lang fsharp>for i in 2..2..8 do

  printf "%d, " i

printfn "done"</lang>

Output:

2, 4, 6, 8, done

Go

This prints all odd digits: <lang go>for i := 1; i < 10; i += 2 {

 fmt.Printf("%d\n", i)

}</lang>

Haskell

<lang haskell>import Control.Monad (forM_) main = do forM_ [2,4..8] (\x -> putStr (show x ++ ", "))

         putStrLn "who do we appreciate?"</lang>

HicEst

<lang hicest>DO i = 1, 6, 1.25 ! from 1 to 6 step 1.25

  WRITE() i

ENDDO</lang>

Icon and Unicon

Icon and Unicon accomplish loop stepping through the use of a generator, the ternary operator to-by, and the every clause which forces a generator to consume all of its results. Because to-by is an operator it has precedence (just higher than assignments) and associativity (left) and can be combined with other operators.

Icon

<lang Icon>

  every 1 to 10 by 2                       # the simplest case that satisfies the task, step by 2

  every 1 to 10                            # no to, step is by 1 by default
  every EXPR1 to EXPR2 by EXPR3 do EXPR4   # general case - EXPRn can be complete expressions including other generators such as to-by, every's do is optional
  steps := [2,3,5,7]                       # a list
  every i := 1 to 100 by !steps            # . more complex, several passes with each step in the list steps, also we might want to know what value we are at
  every L[1 to 100 by 2]                   # as a list index
  every i := 1 to 100 by (k := !steps)     # . need () otherwise := generates an error
  every 1 to 5 to 10                       # simple case of combined to-by - 1,..,10, 2,..10, ..., 5,..,10
  every 1 to 15 by 2 to 5                  # combined to-by
  every (1 to 15 by 2) to 5                # . made explicit

  every writes( (TO_BY_EXPR) | "\n", " " ) # if you want to see how any of these work

</lang> The ability to combine to-by arbitrarily is quite powerful. Yet it can lead to unexpected results. In cases of combined to-by operators the left associativity seems natural where the by is omitted. In cases where the by is used it might seem more natural to be right associative. If in doubt parenthesize.

Unicon

The Icon solution works in Unicon.

J

<lang J> ' who do we appreciate?' ,~ ": 2 * >: i.4 2 4 6 8 who do we appreciate?</lang>

Or, using an actual for loop:

<lang J> 3 :0

 r=.$0
 for_n. 2 * >: i.4 do.
   r=.r,n
 end.
 ' who do we appreciate?' ,~ ":n

) 2 4 6 8 who do we appreciate?</lang>

Java

<lang java>for(int i = 2; i <= 8;i += 2){

  System.out.print(i + ", ");

} System.out.println("who do we appreciate?");</lang>

JavaScript

<lang javascript>var output = ""; for (var i = 2; i <= 8; i += 2)

  output += i + ", ";

output += "who do we appreciate?"; print(output);</lang>

Lisaac

<lang Lisaac>1.to 9 by 2 do { i : INTEGER;

 i.print;
 '\n'.print;

};</lang>

Logo

<lang logo>for [i 2 8 2] [type :i type "|, |] print [who do we appreciate?]</lang>

Lua

<lang lua> for i=2,9,2 do

 print(i)

end </lang>

Output:

2
4
6
8

M4

<lang M4>define(`for',

  `ifelse($#,0,``$0,
  `ifelse(eval($2<=$3),1,
  `pushdef(`$1',$2)$5`'popdef(`$1')$0(`$1',eval($2+$4),$3,$4,`$5')')')')dnl

for(`x',`1',`5',`3',`x ')</lang>

Output:

1
4

Modula-3

<lang modula3>FOR i := 1 TO 100 BY 2 DO

 IO.Put(Fmt.Int(i) & " ");

END;</lang>

MUMPS

<lang MUMPS>FOR I=65:3:122 DO

.WRITE $CHAR(I)," "</lang>

Output:

A D G J M P S V Y \ _ b e h k n q t w z

Objeck

<lang objeck> for(i := 0; i < 10; i += 2;) {

 i->PrintLine();

}; </lang>

OCaml

<lang ocaml># let for_step a b step fn =

   let rec aux i =
     if i <= b then begin
       fn i;
       aux (i+step)
     end
   in
   aux a
 ;;

val for_step : int -> int -> int -> (int -> 'a) -> unit = <fun>

1. for_step 0 8 2 (fun i -> Printf.printf " %d\n" i) ;;

0
2
4
6
8

- : unit = ()</lang>

Octave

<lang octave>for i = 1:2:10

 disp(i)

endfor</lang>

Oz

<lang oz>for I in 2..8;2 do

  {System.show I}

end {System.show done} </lang>

Perl

<lang perl>for($i=2; $i <= 8; $i += 2) {

 print "$i, ";

} print "who do we appreciate?\n";</lang>

Perl 6

Works with: Rakudo version 2010.07

With at least two values on the left-hand side, the series operator (...) can infer an arithmetic series. (With at least three values, it can infer a geometric series, too.)

<lang perl6>for 2, 4 ... 8 {

   print "$_, ";

}

say 'whom do we appreciate?';</lang>

PHP

<lang php><?php foreach (range(2, 8, 2) as $i)

   echo "$i, ";

echo "who do we appreciate?\n"; ?></lang> Output

2, 4, 6, 8, who do we appreciate?

PicoLisp

<lang PicoLisp>(for (N 1 (> 10 N) (+ N 2))

  (printsp N) )</lang>

Pike

<lang pike>int main() {

  for(int i = 2; i <= 16; i=i+2) {
     write(i + "\n");
  }

}</lang>

PL/I

<lang PL/I> declare (n, i) fixed binary;

get list (n); do i = 1 to n by 4;

  put skip list (i);

end; </lang>

PowerShell

<lang powershell>for ($i = 0; $i -lt 10; $i += 2) {

   $i

}</lang>

PureBasic

<lang PureBasic>For i=-15 To 25 Step 5

 Debug i

Next i</lang>

Python

Works with: Python version 2.x

<lang python>for i in xrange(2, 9, 2):

   print "%d," % i,

print "who do we appreciate?"</lang>

Works with: Python version 3.x

<lang python>for i in range(2, 9, 2):

   print("%d, " % i, end="")

print("who do we appreciate?")</lang> Output

2, 4, 6, 8, who do we appreciate?

R

<lang R>for(a in seq(2,8,2)) {

 cat(a, ", ")

} cat("who do we appreciate?\n")</lang>

REBOL

<lang REBOL>for i 2 8 2 [ prin rejoin [i ", "]] print "who do we appreciate?"</lang>

Output:

2, 4, 6, 8, who do we appreciate?

REXX

<lang rexx>do x = 1 to 10 by 1.5

 say x

end</lang>

Output:

1
2.5
4.0
5.5
7.0
8.5
10.0

Ruby

<lang ruby>2.step(8,2) {|n| print "#{n}, "} puts "who do we appreciate?"</lang> or: <lang ruby>(2..8).step(2) {|n| print "#{n}, "} puts "who do we appreciate?"</lang> Output

2, 4, 6, 8, who do we appreciate?

Sather

See Loops/For#Sather: the implementation for for! allows to specify a step, even though the built-in stepto! can be used; an example of usage could be simply: <lang sather> i :INT;

   loop
     i := for!(1, 50, 2);
     -- OR
     -- i := 1.stepto!(50, 2);
     #OUT + i + "\n";
   end;</lang>

(Print all odd numbers from 1 to 50)

Scheme

<lang scheme> (define (for-loop start end step func)

 (let loop ((i start))
   (cond ((< i end)

(func i) (loop (+ i step))))))

(for-loop 2 9 2

 (lambda (i)
   (display i)
   (newline)))

</lang>

Output:

2
4
6
8

Slate

<lang slate>2 to: 8 by: 2 do: [| :i | Console ; i printString ; ', ']. inform: 'enough with the cheering already!'.</lang>

Smalltalk

<lang smalltalk>2 to: 8 by: 2 do: [ :i |

 Transcript show: i; show ', '

]. Transcript showCr: 'enough with the cheering already!'</lang>

Tcl

<lang tcl>for {set i 2} {$i <= 8} {incr i 2} {

   puts -nonewline "$i, "

} puts "enough with the cheering already!"</lang>

TI-89 BASIC

Prints numbers from 0 to 100 stepping by 5.

<lang ti89b>Local i For i, 0, 100, 5

   Disp i

EndFor</lang>

UNIX Shell

Works with: Bourne Again SHell version 3

<lang bash>for (( x=2; $x<=8; x=$x+2 )); do

 printf "%d, " $x

done echo "blah blah blah"</lang>

Vedit macro language

This prints all odd digits in range 1 to 9: <lang vedit>for (#1 = 1; #1 < 10; #1 += 2) {

   Num_Type(#1)

}</lang>

Vorpal

<lang vorpal>for(i = 2, i <= 8, i = i + 2){

  i.print()

}</lang>