gemini - kennedy.gemi.dev

💾 Archived View for sdf.org › rsdoiel › blog › 2020 › 04 › 19 › Mostly-Oberon-Loops-and-Conditions.h… captured on 2023-06-14 at 14:27:38.
-=-=-=-=-=-=-
<!DOCTYPE html>
<html lang="en">
<head>
  <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
  <meta name="language" content="EN">
  <title>Mostly-Oberon-Loops-and-Conditions</title>

  <link rel="stylesheet" type="text/css"  href="/printfonts/print.css" media="print" />
  <link rel="stylesheet" type="text/css"  href="/webfonts/fonts.css" media="screen" />
  <link rel="stylesheet" type="text/css"  href="/css/site.css" media="screen" />
  <link rel="stylesheet" type="text/css"  href="/css/tables.css" media="screen" />
  <link title="RSS feed for rsdoiel's blog" rel="alternate" type="application/rss+xml" href="https://rsdoiel.github.io/rss.xml" />
  <meta name="keywords" content="Oberon, programming">
  <link rel="alternative" type="application/markdown" href="/blog/2020/04/19/Mostly-Oberon-Loops-and-Conditions.md">
  <link rel="search" type="application/opensearchdescription+xml"
        title="Robert's Rambling Search Engine"
        href="search.osdx">
</head>
<body>
<nav>
<ul>
<li><a href="/">R. S. Doiel</a></li>
<li><a href="/about.html">About</a></li>
<li><a href="/blog/">Blog</a></li>
<li><a href="/cv.html">CV</a></li>
<li><a href="https://github.com/rsdoiel">GitHub</a></li>
<li><a href="/library-terminology.html">Library Jargon</a></li>
<li><a href="/presentations.html">Presentations</a></li>
<li><a href="/projects.html">Projects</a></li>
<li><a href="/resume.html">Resume</a></li>
<li><a href="/search.html">Search</a></li>
<li><a href="/series/">Series</a></li>
</ul>
</nav>

<section>
  <article>
  <a data-pocket-label="pocket" data-pocket-count="none" class="pocket-btn" data-lang="en"></a>
<script type="text/javascript">!function(d,i){if(!d.getElementById(i)){var j=d.createElement("script");j.id=i;j.src="https://widgets.getpocket.com/v1/j/btn.js?v=1";var w=d.getElementById(i);d.body.appendChild(j);}}(document,"pocket-btn-js");</script>
<h1 id="oberon-loops-and-conditions">Oberon Loops and Conditions</h1>
<p>By R. S. Doiel, 2020-04-19</p>
<p>This is the four post in the <a
href="../11/Mostly-Oberon.html">Mostly Oberon</a> series. Mostly Oberon
documents my exploration of the Oberon Language, Oberon System and the
various rabbit holes I will inevitably fall into.</p>
<h2 id="data-flow">Data Flow</h2>
<p>Oberon is a small systems language and while it is minimalist. It
provides you with the necessary primitives to get things done. I’ve
touched on code organization, basic types and basic type extensions in
the previous articles. I have shown the basic control statements but
have not talked about them yet.</p>
<p>Oberon offers four basic control statements.</p>
<dl>
<dt>IF, ELSIF, ELSE</dt>
<dd>
Basic condition test and execution
</dd>
<dt>ASSERT</dt>
<dd>
A mechanism to trigger a program halt
</dd>
<dt>WHILE DO, ELSIF DO</dt>
<dd>
The Loop structure in the language (aside from recursive procedures)
</dd>
<dt>FOR TO, FOR TO BY</dt>
<dd>
A counting Loop where incrementing a counter by an integer value (e.g. 1
or by a specified constant).
</dd>
</dl>
<h2 id="if-elsif-else">IF, ELSIF, ELSE</h2>
<p>The first two provide for conditional statements of the form if a
condition is true do something. Almost ever computer language has some
form of a conditional express and the Oberon IF, ELSIF, ELSE typical of
what you find is more computer languages today. Both ELSIF and ELSE are
optional.</p>
<pre class="oberon"><code>    IF (s = &quot;Freda&quot;) OR (s = &quot;Mojo&quot;) THEN
      Out.String(&quot;Wowie Zowie! I remember you from ZBS stories.&quot;);Out.Ln;
    ELSIF (s = &quot;Bilbo&quot;) OR (s = &quot;Gandolf&quot;) THEN
      Out.String(&quot;Greets, I remember from the Hobbit.&quot;);Out.Ln;
    ELSE
      Out.String(&quot;Glad to meet you &quot;);Out.String(s);Out.Ln;
    END;</code></pre>
<h2 id="assert">ASSERT</h2>
<p>The second expression, ASSERT, is a little different. If ASSERT
evaluates an expression that is FALSE then your program is halted. This
is like combining an “if EXPR is false then system exit”.</p>
<pre class="oberon"><code>    Out.String(&quot;Should I continue? Y/n &quot;);
    In.Line(s);
    Out.Ln;
    ASSERT((s = &quot;Y&quot;) OR (s = &quot;y&quot;));
    (* If you didn&#39;t enter Y or y the program will halt *)</code></pre>
<h2 id="while-do-elsif-do">WHILE DO, ELSIF DO</h2>
<p>Oberon-07 also provides two loop structures. These are very similar
to other languages as well. The only expectation is that a while loop
may contain an ELSIF which continues the loop execution until both
clauses return FALSE.</p>
<p>The basic while loop, counting 1 to 10.</p>
<pre class="oberon"><code>    i := 0;
    WHILE i &lt; 10 DO
       i := i + 1;
       Out.Int(i, 1);Out.String(&quot; &quot;);
    END;</code></pre>
<p>A while, elsif loop, counting 1 to 10, then 10 to 100 by 10.</p>
<pre class="oberon"><code>    i := 0;
    WHILE i &lt; 10 DO
       i := i + 1;
       Out.Int(i, 1); Out.String(&quot; &quot;);
    ELSIF i &lt; 100 DO
       i := i + 10;
       Out.Int(i, 1);Out.String(&quot; &quot;);
    END;</code></pre>
<h2 id="for-loops">FOR Loops</h2>
<p>The FOR loop in Oberon is very similar to modern FOR loops. The FOR
loop increments an integer value with in a range. You the default
increments the start value by 1 but if a BY clause is included you can
control how the increment value works.</p>
<p>Regular for loop, <code>i</code> is incremented by 1.</p>
<pre class="oberon"><code>    FOR i := 1 TO 10 DO
       Out.Int(i, 1);Out.String(&quot; &quot;);
    END;</code></pre>
<p>Using a BY clause incrementing <code>i</code> by 2.</p>
<pre class="oberon"><code>    FOR i := 0 TO 20 BY 2  DO
       Out.Int(i, 1);Out.String(&quot; &quot;);
    END;</code></pre>
<h2 id="putting-it-all-together">Putting it all together</h2>
<p>The following <a href="LoopsAndConditions.Mod">module</a>
demonstrates the conditional and loop syntax.</p>
<pre class="oberon"><code>    MODULE LoopsAndConditions;
      IMPORT In, Out;
    
    PROCEDURE IfElsifElseDemo;
      VAR s : ARRAY 128 OF CHAR;
    BEGIN
      Out.String(&quot;Enter your name: &quot;);
      In.Line(s);
      Out.Ln;
      IF (s = &quot;Freda&quot;) OR (s = &quot;Mojo&quot;) THEN
        Out.String(&quot;Wowie Zowie! I remember you from ZBS stories.&quot;);Out.Ln;
      ELSIF (s = &quot;Bilbo&quot;) OR (s = &quot;Gandolf&quot;) THEN
        Out.String(&quot;Greets, I remember from the Hobbit.&quot;);Out.Ln;
      ELSE
        Out.String(&quot;Glad to meet you &quot;);Out.String(s);Out.Ln;
      END;
    END IfElsifElseDemo;
    
    PROCEDURE AssertDemo;
      VAR s : ARRAY 128 OF CHAR;
    BEGIN
      Out.String(&quot;Should I continue? Y/n &quot;);
      In.Line(s);
      Out.Ln;
      ASSERT((s = &quot;Y&quot;) OR (s = &quot;y&quot;));
    END AssertDemo;
    
    PROCEDURE WhileDemo;
      VAR i : INTEGER;
    BEGIN
      Out.String(&quot;Basic WHILE counting from 1 to 10&quot;);Out.Ln;
      i := 0;
      WHILE i &lt; 10 DO
         i := i + 1;
         Out.Int(i, 1);Out.String(&quot; &quot;);
      END;
      Out.Ln;
      Out.String(&quot;WHILE ELSIF, count 1 to 10 THEN 10 to 100&quot;);Out.Ln;
      i := 0;
      WHILE i &lt; 10 DO
         i := i + 1;
         Out.Int(i, 1); Out.String(&quot; &quot;);
      ELSIF i &lt; 100 DO
         i := i + 10;
         Out.Int(i, 1);Out.String(&quot; &quot;);
      END;
      Out.Ln;
      Out.String(&quot;Demo of while loop counting one to ten, then by tenths.&quot;);
    END WhileDemo;
    
    PROCEDURE ForDemo;
      VAR i : INTEGER;
    BEGIN
      Out.String(&quot;Basic FOR LOOP counting from 1 to 10&quot;);Out.Ln;
      FOR i := 1 TO 10 DO
         Out.Int(i, 1);Out.String(&quot; &quot;);
      END;
      Out.Ln;
      Out.String(&quot;FOR loop counting by twos 1 to 20&quot;);Out.Ln;
      FOR i := 0 TO 20 BY 2  DO
         Out.Int(i, 1);Out.String(&quot; &quot;);
      END;
      Out.Ln;
    END ForDemo;
    
    BEGIN
      IfElsifElseDemo;
      AssertDemo;
      WhileDemo;
      ForDemo;
    END LoopsAndConditions.</code></pre>
<h3 id="next-and-previous">Next and Previous</h3>
<ul>
<li>Next <a href="../../05/01/Combining-Oberon-and-C.html">Combining
Oberon-07 and C with OBNC</a></li>
<li>Previous <a href="../18/Mostly-Oberon-Basic-Types.html">Basic
Types</a></li>
</ul>
  </article>
</section>

<footer>
<p>copyright © 2016 - 2023 R. S. Doiel<br /> <a
href="/rssfeed.html">RSS</a> feeds and website built with <a
href="https://rsdoiel.github.io/pttk">pttk</a>, Bash, Make and <a
href="https://pandoc.org">Pandoc</a>.</p>
</footer>
<!-- START: PrettyFi from https://github.com/google/code-prettify -->
<script>
/* We want to add the class "prettyprint" to all the pre elements */
var pre_list = document.querySelectorAll("pre");

pre_list.forEach(function(elem) {
    elem.classList.add("prettyprint");
    elem.classList.add("linenums");/**/
    elem.classList.add("json"); /**/
});
</script>
<style>
li.L0, li.L1, li.L2, li.L3, li.L4, li.L5, li.L6, li.L7, li.L8, li.L9
{
    color: #555;
    list-style-type: decimal;
}
</style>
<link rel="stylesheet" type="text/css" href="/css/prettify.css">
<script src="https://cdn.jsdelivr.net/gh/google/code-prettify@master/loader/run_
prettify.js"></script>
<!--  END: PrettyFi from https://github.com/google/code-prettify -->

</body>
</html>