GoTo statements and alternatives in VB.NET

Question

I've posted a code snippet on another forum asking for help and people pointed out to me that using GoTo statements is very bad programming practice. I'm wondering: why is it bad?

What alternatives to GoTo are there to use in VB.NET that would be considered generally more of a better practice?

Consider this snippet below where the user has to input their date of birth. If the month/date/year are invalid or unrealistic, I'd like to loop back and ask the user again. (I'm using if statements to check the integer's size... if there's a better way to do this, I'd appreciate if you could tell me that also :D)

retryday:
    Console.WriteLine("Please enter the day you were born : ")
    day = Console.ReadLine
    If day > 31 Or day < 1 Then
        Console.WriteLine("Please enter a valid day")
        GoTo retryday
    End If

Answer 1

Your code is fine. It is concise and clear. It is better than inflating the job 50% to 200% with extra variables and different verbs that do the same thing.

If you are just skipping backwards or forwards to the beginning or end of a logical block, then go(to) for it. A "Loop" or an "End while" is still a goto, but the destination is implied. The only advantage is that the compiler will stop you from making two loops cross paths, but it can't with a pair of gotos. When using goto's, don't cross the streams. That would be bad. -- Dr. Spengler

My other pet peeve is the "one entrance, one exit" rule. Of course you can only have one entrance, unless you are writing in assembler. But the "one exit" rule is stupid. It just leads to a bunch of nested bounds checks that walks your code off the right margin. It is much more clear to test all your parameters at the top of the routine and "exit sub" if they are illegal. What makes more sense?

if badparam then
  log error
  exit sub
  endif

if badparam2 then
  log error2
  exit sub
  endif

do stuff

or this?

if goodparam then
  if goodparam2 then
    do stuff
  else
    log error2
    endif
else
  log error 
  endif 

When you have six bounds checks and "stuff" is 60 lines that you can't break up into smaller bits, then the second way turns into a nightmare for anyone who has to maintain it. It's better to finish what you were doing -- checking the exceptions -- than to defer all the exception handling to the end.

My $0.02

Answer 2

I'll throw mine even though the 'by the book' wolves outhere will downvote. Have a look at : Is it ever advantageous to use 'goto' in a language that supports loops and functions? If so, why?