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<div class="section" id="functions">
<h1>Functions<a class="headerlink" href="#functions" title="Permalink to this headline">¶</a></h1>
<p>In this chapter we are going to learn about the next topics :-</p>
<ul class="simple">
<li>Define functions</li>
<li>Call functions</li>
<li>Declare parameters</li>
<li>Send parameters</li>
<li>Main Function</li>
<li>Variables Scope</li>
<li>Program structure</li>
<li>Return Value</li>
<li>Recursion</li>
</ul>
<div class="section" id="define-functions">
<span id="index-0"></span><h2>Define Functions<a class="headerlink" href="#define-functions" title="Permalink to this headline">¶</a></h2>
<p>To define new function</p>
<p>Syntax:</p>
<div class="highlight-none"><div class="highlight"><pre>func <function_name> [parameters]
Block of statements
</pre></div>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">No keyword is required to end the function definition.</p>
</div>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre>func hello
see "Hello from function" + nl
</pre></div>
</div>
</div>
<div class="section" id="call-functions">
<span id="index-1"></span><h2>Call Functions<a class="headerlink" href="#call-functions" title="Permalink to this headline">¶</a></h2>
<p>To call function without parameters, we type the function name then ()</p>
<div class="admonition tip">
<p class="first admonition-title">Tip</p>
<p class="last">We can call the function before the function definition and the function code.</p>
</div>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre>hello()
func hello
see "Hello from function" + nl
</pre></div>
</div>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre>first() second()
func first see "message from the first function" + nl
func second see "message from the second function" + nl
</pre></div>
</div>
</div>
<div class="section" id="declare-parameters">
<h2>Declare parameters<a class="headerlink" href="#declare-parameters" title="Permalink to this headline">¶</a></h2>
<p>To declare the function parameters, after the function name type the list of parameters as a group
of identifiers separated by comma.</p>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre>func sum x,y
see x+y+nl
</pre></div>
</div>
</div>
<div class="section" id="send-parameters">
<h2>Send Parameters<a class="headerlink" href="#send-parameters" title="Permalink to this headline">¶</a></h2>
<p>To send parameters to function, type the parameters inside () after the function name</p>
<p>Syntax:</p>
<div class="highlight-none"><div class="highlight"><pre>funcname(parameters)
</pre></div>
</div>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre>/* output
** 8
** 3000
*/
sum(3,5) sum(1000,2000)
func sum x,y see x+y+nl
</pre></div>
</div>
</div>
<div class="section" id="main-function">
<h2>Main Function<a class="headerlink" href="#main-function" title="Permalink to this headline">¶</a></h2>
<p>Using the Ring programming language, the Main Function is optional,
when it’s defined, it will be executed after the end of other statements.</p>
<p>if no other statements comes alone, the main function will be the first <a class="reference external" href="http://en.wikipedia.org/wiki/Entry_point">entry point</a></p>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre># this program will print the hello world message first then execute the main function
See "Hello World!" + nl
func main
see "Message from the main function" + nl
</pre></div>
</div>
</div>
<div class="section" id="variables-scope">
<h2>Variables Scope<a class="headerlink" href="#variables-scope" title="Permalink to this headline">¶</a></h2>
<p>The Ring programming language uses <a class="reference external" href="http://en.wikipedia.org/wiki/Scope_%28computer_science%29#Lexical_scope_vs._dynamic_scope">lexical scoping</a> to
determine the scope of a variable.</p>
<p>Variables defined inside functions (including function parameters) are local variables.
Variables defined outside functions (before any function) are global variables.</p>
<p>Inside any function we can access the variables defined inside this function beside the global variables.</p>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre># the program will print numbers from 10 to 1
x = 10 # x is a global variable.
func main
for t = 1 to 10 # t is a local variable
mycounter() # call function
next
func mycounter
see x + nl # print the global variable value
x-- # decrement
</pre></div>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">Using the main function before the for loop declare the t variable as a local variable,
It’s recommended to use the main functions instead of typing the instructions directly to set the scope
of the new variables to local.</p>
</div>
</div>
<div class="section" id="program-structure">
<h2>Program Structure<a class="headerlink" href="#program-structure" title="Permalink to this headline">¶</a></h2>
<table border="1" class="docutils">
<colgroup>
<col width="100%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head">Source Code File Sections</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td>Load Files</td>
</tr>
<tr class="row-odd"><td>Statements and Global Variables</td>
</tr>
<tr class="row-even"><td>Functions</td>
</tr>
<tr class="row-odd"><td>Packages and Classes</td>
</tr>
</tbody>
</table>
<p>The application maybe one or more of files.</p>
<p>to include another source file in the project, just use the load command.</p>
<p>Syntax:</p>
<div class="highlight-none"><div class="highlight"><pre>Load "filename.ring"
</pre></div>
</div>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre># File : Start.ring
Load "sub.ring"
sayhello("Mahmoud")
</pre></div>
</div>
<div class="highlight-none"><div class="highlight"><pre># File : sub.ring
func sayhello cName
see "Hello " + cName + nl
</pre></div>
</div>
</div>
<div class="section" id="return-value">
<h2>Return Value<a class="headerlink" href="#return-value" title="Permalink to this headline">¶</a></h2>
<p>The function can return a value using the Return command.</p>
<p>Syntax:</p>
<div class="highlight-none"><div class="highlight"><pre>Return [Expression]
</pre></div>
</div>
<div class="admonition tip">
<p class="first admonition-title">Tip</p>
<p class="last">the Expression after the return command is optional and we can use the return command
to end the function execution without returning any value.</p>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">if the function doesn’t return explicit value, it will return NULL (empty string = “” ).</p>
</div>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre>if novalue() = NULL
See "the function doesn't return a value" + nl
ok
func novalue
</pre></div>
</div>
</div>
<div class="section" id="recursion">
<h2>Recursion<a class="headerlink" href="#recursion" title="Permalink to this headline">¶</a></h2>
<p>The Ring programming language support <a class="reference external" href="http://en.wikipedia.org/wiki/Recursion_%28computer_science%29">Recursion</a>
and the function can call itself using different parameters.</p>
<p>Example:</p>
<div class="highlight-none"><div class="highlight"><pre>see fact(5) # output = 120
func fact x if x = 1 return 1 else return x * fact(x-1) ok
</pre></div>
</div>
</div>
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<ul>
<li><a class="reference internal" href="#">Functions</a><ul>
<li><a class="reference internal" href="#define-functions">Define Functions</a></li>
<li><a class="reference internal" href="#call-functions">Call Functions</a></li>
<li><a class="reference internal" href="#declare-parameters">Declare parameters</a></li>
<li><a class="reference internal" href="#send-parameters">Send Parameters</a></li>
<li><a class="reference internal" href="#main-function">Main Function</a></li>
<li><a class="reference internal" href="#variables-scope">Variables Scope</a></li>
<li><a class="reference internal" href="#program-structure">Program Structure</a></li>
<li><a class="reference internal" href="#return-value">Return Value</a></li>
<li><a class="reference internal" href="#recursion">Recursion</a></li>
</ul>
</li>
</ul>
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