Whats the difference between do while and while in VB.NET?

Question

What's the difference between Do While where the statement is the first line in the loop block and just the single While in VB.NET?

They don't seem to offer any difference in behavior.

There is no difference. One is there for legacy reasons. BASIC is an ooooooold language, and Vb.Net still carries some of that baggage e.g. `Mid(MyStr, 2) = "Hi"` want to guess what that does? — Binary Worrier, Apr 17 '13 at 13:08

score 32 · Accepted Answer · edited Jun 03 '15 at 18:17

32

In Visual Basic these are identical:

    Dim foo As Boolean = True

    While Not foo
        Debug.WriteLine("!")
    End While

    Do While Not foo
        Debug.WriteLine("*")
    Loop

These are not; the do executes once:

    Dim foo As Boolean = True

    While Not foo
        Debug.WriteLine("!")
    End While

    Do
        Debug.WriteLine("*")
    Loop While Not foo

edited Jun 03 '15 at 18:17

Peter Mortensen

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answered Apr 17 '13 at 13:03

dbasnett

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For completeness: `Do While Not …` can be written as `Do Until`. – Konrad Rudolph Apr 17 '13 at 13:04
2

Honestly, I actively avoid `Do Until`. I've seen too may people accidentally throw infinite loops into production code with it. – valverij Apr 17 '13 at 13:05
Great, that's the explanation I was after. – jaffa Apr 17 '13 at 14:56
1

I have always used Do Until. Never had a problem with infinite loops. You just need to make sure you update the variable being tested during the loop. If people are putting infinite loops into production code, then they're not testing it properly. – tolsen64 Aug 08 '16 at 15:17

score 1 · Answer 2 · answered Apr 17 '19 at 03:57

1

In DO...WHILE, the code inside the loop is executed at least once

In WHILE Loop, the code inside the loop is executed 0 or more times.

answered Apr 17 '19 at 03:57

noblepal

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1

score -6 · Answer 3 · edited Jun 03 '15 at 18:20

-6

Do While executes first and then checks if valid. While checks first and then executes.

while (1!=1){ echo 1}

will output nothing

But

do{echo 1} while (1!=1)

will output 1 once.

edited Jun 03 '15 at 18:20

Peter Mortensen

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answered Apr 17 '13 at 10:59

Borniet

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I'm not asking about the difference between do { } while and while { } end while. I'm talking about the do while { }. – jaffa Apr 17 '13 at 11:03
There is no such thing as a do while{} in C# AFAIK – Borniet Apr 17 '13 at 11:24
No it isn't, the DO WHILE is in the same line and the block is underneath. – jaffa Apr 17 '13 at 12:38
Yes, but the logic is the same. – Borniet Apr 17 '13 at 12:39
1

Is this a VB question or a C# question. – dbasnett Apr 17 '13 at 13:04

Whats the difference between do while and while in VB.NET?

3 Answers3