Loops/For: Difference between revisions

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=={{header|APL}}==

~~The~~ APL analogue of a for loop is the '''each''' operator <tt>¨</tt>. The most natural way to accomplish this task doesn't use a nested '''each''', but the '''repeat''' operator <tt>/</tt> inside a single '''each''':

For most purposes, the APL analogue of a for loop is the '''each''' operator <tt>¨</tt>. The most natural way to accomplish this task doesn't use a nested '''each''', but the '''repeat''' operator <tt>/</tt> inside a single '''each''':

<lang APL>stars ← { ⍵ 1 ⍴ {⍵/'*'}¨⍳⍵ }</lang>

~~However, to~~ stick to the letter of the task description, we can nest an '''each''' inside another one. ~~This becomes less portable as~~ it ~~relies on '''⎕ucs''~~' ~~to generate~~ a ~~newline, assumes that newline is character 10, and requires support for multiple statements inside an anonymous function (dfn, <tt>{</tt> ... <tt>}</tt>), which e.g. GNU APL does not~~ ~~have~~:

To stick to the letter of the task description, we can nest an '''each''' inside another one, but it's a little silly:

<lang APL>stars ← { ⍵ 1 ⍴ { {'*'} ¨ ⍳⍵} ¨ ⍳⍵ }</lang>

Additionally, Dyalog and some other dialects support the more traditional structured programming controls inside a named function definition (tradfn):

<lang APL>∇result ← stars count; i; j; vec

vec ← ⍬

:for i :in ⍳ count

vec ,← ⊂''

:for j :in ⍳ i

vec[i],←'*'

:endfor

result ← count 1 ⍴ vec

∇</lang>

The result of all three implementations of `stars` is a column vector, which is displayed like this:

The output of both versions is the same:

<pre>*

<pre> stars 5

*

**

***