This is the problem:
private static void Swap(ref int first, ref int middle, ref int last);
   int temp;
    temp = firstInt;
    firstInt = lastInt;
    lastInt = temp;
   }
You have a ; after the parameter list of your method Swap, when it should be a { (curly brace):
private static void Swap(ref int first, ref int middle, ref int last)
{
    int temp;
    temp = firstInt;
    firstInt = lastInt;
    lastInt = temp;
}
Your code generates a “Type or namespace definition, or end-of-file expected.” error.
EDIT
As others have pointed out, you also have the wrong variables name – it should be first, middle and last, so you’re whole method would be:
private static void Swap(ref int first, ref int middle, ref int last)
{
    int temp;
    temp = first;
    first = last;
    last = temp;
}
solved trouble with swapping firstInt, middleInt, and lastInt [closed]