添加中划线:

  UILabel * strikeLabel = [[UILabel alloc] initWithFrame:(CGRectMake(10, 10, 50, 30))];
  NSString *textStr = [NSString stringWithFormat:@"%@元", primeCost];

  //中划线
  NSDictionary *attribtDic = @{NSStrikethroughStyleAttributeName: [NSNumber numberWithInteger:NSUnderlineStyleSingle]};
  NSMutableAttributedString *attribtStr = [[NSMutableAttributedString alloc]initWithString:textStr attributes:attribtDic];

  // 赋值
  strikeLabel.attributedText = attribtStr;

  [self.view addSubview:strikeLabel];

添加下划线:

UILabel *underlineLabel = [[UILabel alloc] initWithFrame:(CGRectMake(10, 10, 50, 30))];
  NSString *textStr = [NSString stringWithFormat:@"%@元", primeCost];

  // 下划线
  NSDictionary *attribtDic = @{NSUnderlineStyleAttributeName: [NSNumber numberWithInteger:NSUnderlineStyleSingle]};
  NSMutableAttributedString *attribtStr = [[NSMutableAttributedString alloc]initWithString:textStr attributes:attribtDic];

  //赋值
  underlineLabel.attributedText = attribtStr;

  [self.view addSubview:underlineLabel];