C#: How can I combine a switch with an if-statement?

Question

I need to combine a switch with an if-statement.

How can I do that? I want to do something like this:

switch (periodtype)
{
    if(starttime>endtime)
    {
        ;
    }
    else
    {
        case 0: nextRunTime = nextRunTime.AddHours(period); break;
        case 1: nextRunTime = nextRunTime.AddMinutes(period); break;
        case 2: nextRunTime = nextRunTime.AddSeconds(period); break;
    }
}

Answer 1

if(starttime>endtime)
{
    // Stuff
}
else
{
    switch (periodtype)
    {
        case 0: nextRunTime = nextRunTime.AddHours(period); break;
        case 1: nextRunTime = nextRunTime.AddMinutes(period); break
        case 2: nextRunTime = nextRunTime.AddSeconds(period); break;
    }
}

Like that?

Answer 2

What's wrong with:

if(starttime<=endtime)
{
    switch (periodtype)
    {
        case 0: nextRunTime = nextRunTime.AddHours(period); break;
        case 1: nextRunTime = nextRunTime.AddMinutes(period); break;
        case 2: nextRunTime = nextRunTime.AddSeconds(period); break;
    }
}

Answer 3

if(starttime>endtime)
{
    ;
}
else
{
   switch (periodtype)
   {
      case 0: nextRunTime = nextRunTime.AddHours(period); break;
      case 1: nextRunTime = nextRunTime.AddMinutes(period); break;
      case 2: nextRunTime = nextRunTime.AddSeconds(period); break;
   }
}

Answer 4

if(starttime <= endtime)
{
      switch (periodtype)
      {     
             case 0: nextRunTime = nextRunTime.AddHours(period); break;
             case 1: nextRunTime = nextRunTime.AddMinutes(period); break;
             case 2: nextRunTime = nextRunTime.AddSeconds(period); break;

       }
}

Answer 5

Hmm way too late with answer

isnt this easier:

if (starttime <= endtime)
{
    switch (periodtype)
    { 
     case 0: nextRunTime = nextRunTime.AddHours(period); break;
     case 1: nextRunTime = nextRunTime.AddMinutes(period); break;
     case 2: nextRunTime = nextRunTime.AddSeconds(period); break;
    }
}