title: ObjC - Using NSRange, Allow User to Enter Only One decimal point -
body: <p>building a simple calculator here to get my feet wet with iOS dev. I want to prohibit the entry of more than one decimal point. Put my logic in the comment.</p>
  
  <p>It builds and runs with no problem, but it's not blocking the entry of more than one "." any help is appreciated. Thanks.</p>
  
  <pre><code>- (IBAction)digitPressed:(UIButton *)sender
  {
      NSString *digit = [[sender titleLabel] text];
      if (userIsInTheMiddleofTypingANumber) {
          [display setText:[[display text] stringByAppendingString:digit]];
          // if the user enters a decimal point, check if the existing display text contains a "." if not, then allow it, but if it does, do not allow it.
          NSString *decimal = @".";
          NSRange range = [digit rangeOfString:decimal];
              if (range.location == NSNotFound) {
                  [display setText:digit];
              }
  
      } else {
          [display setText:digit];
          userIsInTheMiddleofTypingANumber = YES;
      }
  }
  </code></pre>