I'm sure this is just a simple problem that I cannot find the answer to, but it is driving me crazy. I am declaring the QString variables oldName and oldAddress in my constructor function, but then when I try to use them in a function that I have in a slot, then I get the error "oldName was not declared in this scope"

Here is the relavent snippet of my code.

Qt Code: 
  1. MainWindow::MainWindow(QWidget *parent) :
  2.     QMainWindow(parent),
  3.     ui(new Ui::MainWindow)
  4. {
  5.     ui->setupUi(this);
  6.     ui->pushButton_2->hide();
  7.     ui->pushButton_3->hide();
  8.     ui->lineEdit->setReadOnly(true);
  9.     ui->textEdit->setReadOnly(true);
  10.     QString oldName;
  11.     QString oldAddress;
  12. }
  13.  
  14. MainWindow::~MainWindow()
  15. {
  16.     delete ui;
  17. }
  18.  
  19. void MainWindow::add()
  20. {
  21.     ui->pushButton_2->show();
  22.     ui->pushButton_3->show();
  23.     ui->pushButton->setEnabled(false);
  24.     ui->lineEdit->setReadOnly(false);
  25.     ui->textEdit->setReadOnly(false);
  26.  
  27.     oldName = ui->lineEdit->text();
  28.     oldAddress = ui->textEdit->toPlainText();
  29. }
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Thank you for your help in advance