title: Incompatible types in initialization error
body: <p>I've been on this for hours and can't find a solution. When I try to compile the following I get the "Incompatible types in initialization" error on the marked lines. Any help is accepted.</p>
  
  <p>Here's my <em>Controller.m</em> file:</p>
  
  <pre><code>#import "Controller.h"
  #import "Transactions.h"
  
  @implementation Controller
  - (IBAction)add:(id)sender {
      double x = [addF doubleValue];
      double bal = [balanceF doubleValue];
      double newBal = [trans add:x to:bal]; //Error marked here
      [balanceF setDoubleValue:newBal];
  }
  
  - (IBAction)sub:(id)sender {
      double x = [subF doubleValue];
      double bal = [balanceF doubleValue];
      double newBal = [trans sub:x from:bal]; //Error marked here
      [balanceF setDoubleValue:newBal];
  }
  @end
  </code></pre>
  
  <p>And here's my <em>Transactions.m</em> file:</p>
  
  <pre><code>#import "Transactions.h"
  
  @implementation trans
  
  -(double) add:(double)x to:(double)bal{
      return (x + bal);
  }
  
  -(double) sub:(double)x from:(double)bal{
      return (bal - x);
  }
  
  @end
  </code></pre>
  
  <p>Please tell me if you need anything else.
  Thanks!</p>