void QLineEdit::textChanged ( const QString & text )void QLineEdit::textEdited ( const QString & text )
connect( LineEdit, SIGNAL( textChanged( const QString& ) ), SLOT( sum() ) );connect( LineEdit_2, SIGNAL( textChanged( const QString& ) ), SLOT( sum() ) );
void Class::sum(){ label->setText( QString( "%1" ).arg( LineEdit->text().toInt() + LineEdit_2->text().toInt() ) );}Код примерный!