Wiring the Qt Widgets application logic

The application logic for the calculator is simple: we add a property setter to ResultDialog that lets us set the result field of the dialog, and then we wire up some arithmetic, signals, and slots in MainWindow, to do the actual computation and show the dialog. Let's have a look at the following steps:

1. First, make the following change to ResultDialog:

void ResultDialog::setResult(float r) 
{ 
    ui->result->setText(QString::number(r)); 
} 

This method takes a float, the value to show in the dialog, and formats the result as a string, using Qt's default formatting. Qt is fully internationalized; if you do this in English-speaking locales, it will use a decimal point, whereas if you do it with a locale set to a region where a comma is used as the decimal separator, it will use a comma instead. The number method is a handy...