title: objective-c converting strings to usable numbers
body: <p>I have strings that look about like this:</p>
  
  <pre><code>stringA = @"29.88";
  stringB = @"2564";
  stringC = @"12";
  stringD = @"-2";
  </code></pre>
  
  <p>what is the best way to convert them so they can all be used in the same mathmatical formula?? that includes add, subtract.multiply,divide etc</p>