title: Convert NSString to double for calculations and then back again to print in NSString
body: <p>I accept NSString as</p>
  
  <pre><code>NSString *value = [valuelist objectAtIndex:valuerow];
  NSString *value2 = [valuelist2 objectAtIndex:valuerow2];
  </code></pre>
  
  <p>from UIPickerView.
  I want to </p>
  
  <pre><code>double *cal = value + (value2 * 8) + 3;
  
  
  NSString *message =[[NSString alloc] initWithFormat:@"%@",cal];
  </code></pre>
  
  <p>I should be able to get the string in message after I do the calculations on it .. Please help
  My program is crashing</p>