Switch when

// if current hour is in between 0-12 >> Good Morning
// else if current hour is in between 12 to 17 >> Good Afternoon
// else >> Good Evening

Integer currentHour = 12;

switch on currentHour {
    when 0,1,2,3,4,5,6,7,8,9,10,11{
        System.debug('Good Morning');
    }
    when 12,13,14,15,16{
        System.debug('Good Afternoon');
    }
    when else {
        System.debug('Good Evening');
    }
}

// if current hour is in between 0-12 >> Good Morning
// else if current hour is in between 12 to 17 >> Good Afternoon
// else >> Good Evening

Integer currentHour = 12;

switch on currentHour {
    when 0..11{
        System.debug('Good Morning');
    }
    when 12..16{
        System.debug('Good Afternoon');
    }
    when else {
        System.debug('Good Evening');
    }
}