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<div class="section" id="functions-first-style">
<span id="index-0"></span><h1>Functions - First Style<a class="headerlink" href="#functions-first-style" 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><p>Define functions</p></li>
<li><p>Call functions</p></li>
<li><p>Declare parameters</p></li>
<li><p>Send parameters</p></li>
<li><p>Main Function</p></li>
<li><p>Variables Scope</p></li>
<li><p>Return Value</p></li>
<li><p>Recursion</p></li>
</ul>
<div class="section" id="define-functions">
<span id="index-1"></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-ring notranslate"><div class="highlight"><pre><span></span><span class="k">func</span> <span class="o"><</span><span class="n">function_name</span><span class="o">></span> <span class="o">[</span><span class="n">parameters</span><span class="o">]</span>
<span class="n">Block</span> <span class="n">of</span> <span class="n">statements</span>
</pre></div>
</div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>No keyword is required to end the function definition.</p>
</div>
<p>Example:</p>
<div class="highlight-ring notranslate"><div class="highlight"><pre><span></span><span class="k">func</span> <span class="n">hello</span>
<span class="k">see</span> <span class="s">"Hello from function"</span> <span class="o">+</span> <span class="n">nl</span>
</pre></div>
</div>
</div>
<div class="section" id="call-functions">
<span id="index-2"></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="admonition-title">Tip</p>
<p>We can call the function before the function definition and the function code.</p>
</div>
<p>Example:</p>
<div class="highlight-ring notranslate"><div class="highlight"><pre><span></span><span class="n">hello</span><span class="p">()</span>
<span class="k">func</span> <span class="n">hello</span>
<span class="k">see</span> <span class="s">"Hello from function"</span> <span class="o">+</span> <span class="n">nl</span>
</pre></div>
</div>
<p>Example:</p>
<div class="highlight-ring notranslate"><div class="highlight"><pre><span></span><span class="n">first</span><span class="p">()</span> <span class="n">second</span><span class="p">()</span>
<span class="k">func</span> <span class="n">first</span> <span class="k">see</span> <span class="s">"message from the first function"</span> <span class="o">+</span> <span class="n">nl</span>
<span class="k">func</span> <span class="n">second</span> <span class="k">see</span> <span class="s">"message from the second function"</span> <span class="o">+</span> <span class="n">nl</span>
</pre></div>
</div>
</div>
<div class="section" id="declare-parameters">
<span id="index-3"></span><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-ring notranslate"><div class="highlight"><pre><span></span><span class="k">func</span> <span class="n">sum</span> <span class="n">x</span><span class="p">,</span><span class="n">y</span>
<span class="k">see</span> <span class="n">x</span><span class="o">+</span><span class="n">y</span><span class="o">+</span><span class="n">nl</span>
</pre></div>
</div>
</div>
<div class="section" id="send-parameters">
<span id="index-4"></span><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-ring notranslate"><div class="highlight"><pre><span></span><span class="n">funcname</span><span class="p">(</span><span class="n">parameters</span><span class="p">)</span>
</pre></div>
</div>
<p>Example:</p>
<div class="highlight-ring notranslate"><div class="highlight"><pre><span></span><span class="o">/*</span> <span class="n">output</span>
<span class="o">**</span> <span class="mi">8</span>
<span class="o">**</span> <span class="mi">3000</span>
<span class="o">*/</span>
<span class="n">sum</span><span class="p">(</span><span class="mi">3</span><span class="p">,</span><span class="mi">5</span><span class="p">)</span> <span class="n">sum</span><span class="p">(</span><span class="mi">1000</span><span class="p">,</span><span class="mi">2000</span><span class="p">)</span>
<span class="k">func</span> <span class="n">sum</span> <span class="n">x</span><span class="p">,</span><span class="n">y</span> <span class="k">see</span> <span class="n">x</span><span class="o">+</span><span class="n">y</span><span class="o">+</span><span class="n">nl</span>
</pre></div>
</div>
</div>
<div class="section" id="main-function">
<span id="index-5"></span><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-ring notranslate"><div class="highlight"><pre><span></span><span class="c"># this program will print the hello world message first then execute the main function</span>
<span class="k">See</span> <span class="s">"Hello World!"</span> <span class="o">+</span> <span class="n">nl</span>
<span class="k">func</span> <span class="n">main</span>
<span class="k">see</span> <span class="s">"Message from the main function"</span> <span class="o">+</span> <span class="n">nl</span>
</pre></div>
</div>
</div>
<div class="section" id="variables-scope">
<span id="index-6"></span><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-ring notranslate"><div class="highlight"><pre><span></span><span class="c"># the program will print numbers from 10 to 1</span>
<span class="n">x</span> <span class="o">=</span> <span class="mi">10</span> <span class="c"># x is a global variable.</span>
<span class="k">func</span> <span class="n">main</span>
<span class="k">for</span> <span class="n">t</span> <span class="o">=</span> <span class="mi">1</span> <span class="k">to</span> <span class="mi">10</span> <span class="c"># t is a local variable</span>
<span class="n">mycounter</span><span class="p">()</span> <span class="c"># call function</span>
<span class="k">next</span>
<span class="k">func</span> <span class="n">mycounter</span>
<span class="k">see</span> <span class="n">x</span> <span class="o">+</span> <span class="n">nl</span> <span class="c"># print the global variable value</span>
<span class="n">x</span><span class="o">--</span> <span class="c"># decrement</span>
</pre></div>
</div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>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="return-value">
<span id="index-7"></span><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-ring notranslate"><div class="highlight"><pre><span></span><span class="k">Return</span> <span class="o">[</span><span class="n">Expression</span><span class="o">]</span>
</pre></div>
</div>
<div class="admonition tip">
<p class="admonition-title">Tip</p>
<p>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="admonition-title">Note</p>
<p>if the function doesn’t return explicit value, it will return NULL (empty string = “” ).</p>
</div>
<p>Example:</p>
<div class="highlight-ring notranslate"><div class="highlight"><pre><span></span><span class="k">if</span> <span class="n">novalue</span><span class="p">()</span> <span class="o">=</span> <span class="kp">NULL</span>
<span class="k">See</span> <span class="s">"the function doesn't return a value"</span> <span class="o">+</span> <span class="n">nl</span>
<span class="k">ok</span>
<span class="k">func</span> <span class="n">novalue</span>
</pre></div>
</div>
</div>
<div class="section" id="recursion">
<span id="index-8"></span><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-ring notranslate"><div class="highlight"><pre><span></span><span class="k">see</span> <span class="n">fact</span><span class="p">(</span><span class="mi">5</span><span class="p">)</span> <span class="c"># output = 120</span>
<span class="k">func</span> <span class="n">fact</span> <span class="n">x</span> <span class="k">if</span> <span class="n">x</span> <span class="o">=</span> <span class="mi">0</span> <span class="k">return</span> <span class="mi">1</span> <span class="k">else</span> <span class="k">return</span> <span class="n">x</span> <span class="o">*</span> <span class="n">fact</span><span class="p">(</span><span class="n">x</span><span class="o">-</span><span class="mi">1</span><span class="p">)</span> <span class="k">ok</span>
</pre></div>
</div>
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