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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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<title>Control Structures — Ring 1.0 documentation</title>
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<div class="section" id="control-structures">
<h1>Control Structures<a class="headerlink" href="#control-structures" title="Permalink to this headline">¶</a></h1>
<p>In this chapter we are going to learn about the control structures provided by
the Ring programming language.</p>
<div class="section" id="branching">
<span id="index-0"></span><h2>Branching<a class="headerlink" href="#branching" title="Permalink to this headline">¶</a></h2>
<ul class="simple">
<li>If Statement</li>
</ul>
<p>Syntax:</p>
<div class="highlight-none"><div class="highlight"><pre>if Expression
Block of statements
but Expression
Block of statements
else
Block of statements
ok
</pre></div>
</div>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre>see "
Main Menu
---------
(1) Say Hello
(2) About
(3) Exit
" give nOption
if nOption = 1 see "Enter your name : " give name see "Hello " + name + nl
but nOption = 2 see "Sample : using if statement" + nl
but nOption = 3 bye
else see "bad option..." + nl
ok
</pre></div>
</div>
<ul class="simple">
<li>Switch Statement</li>
</ul>
<p>Syntax:</p>
<div class="highlight-none"><div class="highlight"><pre>switch Expression
on Expression
Block of statements
other
Block of statements
off
</pre></div>
</div>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre>See "
Main Menu
---------
(1) Say Hello
(2) About
(3) Exit
" Give nOption
Switch nOption
On 1 See "Enter your name : " Give name See "Hello " + name + nl
On 2 See "Sample : using switch statement" + nl
On 3 Bye
Other See "bad option..." + nl
Off
</pre></div>
</div>
</div>
<div class="section" id="looping">
<span id="index-1"></span><h2>Looping<a class="headerlink" href="#looping" title="Permalink to this headline">¶</a></h2>
<ul class="simple">
<li>While Loop</li>
</ul>
<p>Syntax:</p>
<div class="highlight-none"><div class="highlight"><pre>while Expression
Block of statements
end
</pre></div>
</div>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre>While True
See "
Main Menu
---------
(1) Say Hello
(2) About
(3) Exit
" Give nOption
Switch nOption
On 1
See "Enter your name : "
Give name
See "Hello " + name + nl
On 2
See "Sample : using while loop" + nl
On 3
Bye
Other
See "bad option..." + nl
Off
End
</pre></div>
</div>
<ul class="simple">
<li>For Loop</li>
</ul>
<p>Syntax:</p>
<div class="highlight-none"><div class="highlight"><pre>for identifier=expression to expression [step expression]
Block of statements
next
</pre></div>
</div>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre># print numbers from 1 to 10
for x = 1 to 10 see x + nl next
</pre></div>
</div>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre># Dynamic loop
See "Start : " give nStart
See "End : " give nEnd
See "Step : " give nStep
For x = nStart to nEnd Step nStep
see x + nl
Next
</pre></div>
</div>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre># print even numbers from 0 to 10
for x = 0 to 10 step 2
see x + nl
next
</pre></div>
</div>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre># print even numbers from 10 to 0
for x = 10 to 0 step -2
see x + nl
next
</pre></div>
</div>
<ul class="simple">
<li>For in Loop</li>
</ul>
<p>Syntax:</p>
<div class="highlight-none"><div class="highlight"><pre>for identifier in List/String [step expression]
Block of statements
next
</pre></div>
</div>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre>aList = 1:10 # create list contains numbers from 1 to 10
for x in aList see x + nl next # print numbers from 1 to 10
</pre></div>
</div>
</div>
<div class="section" id="using-the-step-option-with-for-in">
<span id="index-2"></span><h2>Using The Step option with For in<a class="headerlink" href="#using-the-step-option-with-for-in" title="Permalink to this headline">¶</a></h2>
<p>We can use the Step option with For in to skip number of items in each iteration</p>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre>aList = 1:10 # create list contains numbers from 1 to 10
# print odd items inside the list
for x in aList step 2
see x + nl
next
</pre></div>
</div>
</div>
<div class="section" id="using-for-in-to-modify-lists">
<span id="index-3"></span><h2>Using For in to modify lists<a class="headerlink" href="#using-for-in-to-modify-lists" title="Permalink to this headline">¶</a></h2>
<p>When we use (For in) we get items by reference.</p>
<p>This means that we can read/edit items inside the loop.</p>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre>aList = 1:5 # create list contains numbers from 1 to 5
# replace list numbers with strings
for x in aList
switch x
on 1 x = "one"
on 2 x = "two"
on 3 x = "three"
on 4 x = "four"
on 5 x = "five"
off
next
see aList # print the list items
</pre></div>
</div>
</div>
<div class="section" id="do-again-loop">
<span id="index-4"></span><h2>Do Again Loop<a class="headerlink" href="#do-again-loop" title="Permalink to this headline">¶</a></h2>
<p>Syntax:</p>
<div class="highlight-none"><div class="highlight"><pre>do
Block of statements
again expression
</pre></div>
</div>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre>x = 1
do
see x + nl
x++
again x <= 10
</pre></div>
</div>
</div>
<div class="section" id="exit-command">
<span id="index-5"></span><h2>Exit Command<a class="headerlink" href="#exit-command" title="Permalink to this headline">¶</a></h2>
<p>Used to go outside one or more of loops.</p>
<p>Syntax:</p>
<div class="highlight-none"><div class="highlight"><pre>exit [expression] # inside loop
</pre></div>
</div>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre>for x = 1 to 10
see x + nl
if x = 5 exit ok
next
</pre></div>
</div>
</div>
<div class="section" id="exit-from-two-loops">
<h2>Exit from two loops<a class="headerlink" href="#exit-from-two-loops" title="Permalink to this headline">¶</a></h2>
<p>The next example presents how to use the exit command to exit from two loops in one jump.</p>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre>for x = 1 to 10
for y = 1 to 10
see "x=" + x + " y=" + y + nl
if x = 3 and y = 5
exit 2 # exit from 2 loops
ok
next
next
</pre></div>
</div>
<ul class="simple" id="index-6">
<li>Loop Command</li>
</ul>
<p>Used to jump to the next iteration in the loop.</p>
<p>Syntax:</p>
<div class="highlight-none"><div class="highlight"><pre>loop [expression] # inside loop
</pre></div>
</div>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre>for x = 1 to 10
if x = 3
see "Number Three" + nl
loop
ok
see x + nl
next
</pre></div>
</div>
</div>
<div class="section" id="exit-loop-inside-sub-functions">
<h2>Exit/Loop inside sub functions<a class="headerlink" href="#exit-loop-inside-sub-functions" title="Permalink to this headline">¶</a></h2>
<p>While we are inside a loop, we can call a function then use the exit and/or loop command
inside that function and the command will work on the outer loop.</p>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre># print numbers from 1 to 10 except number 5.
for x = 1 to 10
ignore(x,5)
see x + nl
next
func ignore x,y
if x = y
loop
ok
</pre></div>
</div>
</div>
<div class="section" id="short-circuit-evaluation">
<span id="index-7"></span><h2>Short-circuit evaluation<a class="headerlink" href="#short-circuit-evaluation" title="Permalink to this headline">¶</a></h2>
<p>The logical operators and/or follow the <a class="reference external" href="http://en.wikipedia.org/wiki/Short-circuit_evaluation">short-circuit evaluation</a>.</p>
<p>If the first argument of the AND operator is zero, then there is no need to evaluate the second
argument and the result will be zero.</p>
<p>If the first argument of the OR operator is one, then there is no need to evaluate the second
argument and the result will be one.</p>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre>/* output
** nice
** nice
** great
*/
x = 0 y = 10
if (x = 0 and nice()) and (y = 10 and nice())
see "great" + nl
ok
func nice see "nice" + nl return 1
</pre></div>
</div>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre># No output
x = 0 y = 10
if (x = 1 and nice()) and (y = 10 and nice())
see "great" + nl
ok
func nice see "nice" + nl return 1
</pre></div>
</div>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre>/* output
** nice
** great
*/
x = 0 y = 10
if (x = 0 and nice()) or (y = 10 and nice())
see "great" + nl
ok
func nice see "nice" + nl return 1
</pre></div>
</div>
</div>
<div class="section" id="comments-about-evaluation">
<h2>Comments about evaluation<a class="headerlink" href="#comments-about-evaluation" title="Permalink to this headline">¶</a></h2>
<ul class="simple">
<li>True, False, nl & NULL are variables defined by the language</li>
<li>True = 1</li>
<li>False = 0</li>
<li>nl = new line</li>
<li>NULL = empty string = “”</li>
<li>Everything evaluates to true except 0 (False).</li>
</ul>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre># output = message from the if statement
if 5 # 5 evaluates to true because it's not zero (0).
see "message from the if statement" + nl
ok
</pre></div>
</div>
</div>
</div>
</div>
</div>
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<h3><a href="index.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">Control Structures</a><ul>
<li><a class="reference internal" href="#branching">Branching</a></li>
<li><a class="reference internal" href="#looping">Looping</a></li>
<li><a class="reference internal" href="#using-the-step-option-with-for-in">Using The Step option with For in</a></li>
<li><a class="reference internal" href="#using-for-in-to-modify-lists">Using For in to modify lists</a></li>
<li><a class="reference internal" href="#do-again-loop">Do Again Loop</a></li>
<li><a class="reference internal" href="#exit-command">Exit Command</a></li>
<li><a class="reference internal" href="#exit-from-two-loops">Exit from two loops</a></li>
<li><a class="reference internal" href="#exit-loop-inside-sub-functions">Exit/Loop inside sub functions</a></li>
<li><a class="reference internal" href="#short-circuit-evaluation">Short-circuit evaluation</a></li>
<li><a class="reference internal" href="#comments-about-evaluation">Comments about evaluation</a></li>
</ul>
</li>
</ul>
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