changing lineEdit property in qtcreator

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QT

QT-Creator

hi i am beginner in qt
i created a GUI application in qt creator and added a push button and a line edit into form by desginer. i want the size of (width and height) lineEdit change when i click push button
but when i write this code:

void MainWindow::on_pushButton_clicked()
{
    lineEdit->setGeometry( 0, 0, 85, 30 );
}

it gives thiserror :

C:\Users\REZA\Documents\Qt\game4-build-desktop\..\game4\mainwindow.cpp:19: error: 'lineEdit' was not declared in this scope