title: Implicit declaration of function "..." is invalid in C99?
body: <p>I'm trying to declare a function within another function. So here's part of my code:
  ViewController.m</p>
  
  <pre><code>- (void)updatedisplay{
      [_displayText setText:[NSString stringWithFormat:@"%d", counter]];
  
  }
  
  - (IBAction)minus1:(id)sender {
      counter--;
      updatedisplay();
  }
  </code></pre>
  
  <p>ViewController.h</p>
  
  <pre><code>- (IBAction)minus1:(id)sender;
  - (void)updatedisplay;
  </code></pre>
  
  <p>Which returned me the error of "Implicit declaration of function "..." is invalid in C99".</p>
  
  <p>Result: <a href="https://i.imgur.com/rsIt6r2.png" rel="noreferrer">http://i.imgur.com/rsIt6r2.png</a></p>
  
  <p>I've found that people have encountered similar problem, but as a newbie I didn't really know what to do next. Thanks for your help! :)</p>
  
  <p><a href="https://stackoverflow.com/questions/17583497/implicit-declaration-of-function-is-invalid-on-c99">Implicit declaration of function &#39;...&#39; is invalid on C99</a></p>