title: error: a parameter list without types is only allowed in a function definition
body: <p>I'm learning how to create and use functions. My code doesn't compile but I can't seem to figure out what I'm doing wrong.</p>
  
  <p>Here is my code:</p>
  
  <pre><code>#include &lt;stdio.h&gt;
  #include &lt;cs50.h&gt;
  #include &lt;stdbool.h&gt;
  
  bool tri (double x, double y, double z);
  
  int main(void)
  {
      double x = get_double("Give:");
      double y = get_double("Another:");
      double z = get_double("Now:");
  
      bool tri (x, y, z);
  }
  
  bool tri (double x, double y, double z)
  {
      if (x&lt;1 || y&lt;1 || z&lt;1)
      {
          return false;
      }
  
      if (x+y &gt; z &amp;&amp; y+z &gt; x &amp;&amp; z+x &gt; y)
      {
          return true;
      }
  
      else
      {
          return false;
      }
  }
  </code></pre>
  
  <p>When I try to compile this code, I get the following error:</p>
  
  <pre><code>error: a parameter list without types is only allowed in a function definition
  bool tri (x, y, z);
            ^
  </code></pre>