Tag Archives: While

Break From a Nested Loop

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I’m building a new version of my “Multi-Level Menu System with a Back Option.” Here’s the URL from the May 2016 post: http://tommymaynard.com/script-sharing-multi-level-menu-system-with-back-option-2016. This is a post where I wrote about creating a text based nested menu system. It was neat, but the nested Switch statements got a little confusing, and so it was never used by me, or potentially anyone else. I have no idea.

What I do know, is that a few times this past weekend I was able to work on a redesign for this menu system. The problem was this: From the main menu, you can press Q to quit. In the nested menus you either choose an option (1 through whatever), or press B to go back a menu. This means that if you’re three menus deep, you have to press B until you’re back at the main menu in order to press Q to quit. You can’t quit from a nested menu. Well, you couldn’t before this weekend, anyway.

We won’t go into the menu system for now, but I do want to leave an example of how to break out of nested loops. I seriously, learned something I’ve yet to ever see, and so maybe this will be a first for you, as well. We’ve all seen, and likely used break. You can read more at about_break using Get-Help: Get-Help -Name about_Break -ShowWindow.

In this first example, we’ll write the string “This is a test.” until we stop the loop’s execution. There’s nothing about this loop that’s ever going to make it stop without our help.

While ($true) {
    'This is a test.'
}

'This is a test.'
'This is a test.'
'This is a test.'
...

In this next example, we’ll immediately break out of the While loop by using the break statement. Prior to breaking out, we’ll write “This is a test.” to the host program, but this time, it’ll only be written once and then the execution will end.

While ($true) {
    'This is a test.'
    break
}
'This is a test.'

Let’s start our next example by nesting a While loop, inside of a While loop. In this example, we’ll write “Outer While loop” once, and then continually write “Nested While loop” until we manually end the execution. We can’t get back to the outer While loop, when we’re forever stuck in the inner While loop.

While ($true) {
    'Outer While loop'

    While ($true) {
        'Nested While loop'
    }
}
'Outer While loop'
'Nested While loop'
'Nested While loop'
'Nested While loop'
...

This next example includes a break statement inside the nested While loop. This means we’ll write “Outer While loop” and “Nested While loop” over and over, forever. We’ll at least until we stop the execution. In this example, we can get back to the outer While loop.

While ($true) {
    'Outer While loop'

    While ($true) {
        'Nested While loop'
        break
    }
}
'Outer While loop'
'Nested While loop'
'Outer While loop'
'Nested While loop'
'Outer While loop'
'Nested While loop'
...

Our final example, will include the word outer, after the break statement. In this example, we’ll execute the outer While loop, execute the inner While loop, and then break out of both of the While loops. Yes both, from inside the inner loop.

I didn’t even know this was possible before the weekend. My nested menu system is absolutely going to need this! Now, I can allow my users to quit, no matter how deep their level nestation — yes, I totally just made up that word. Enjoy, and maybe it’s helpful for you one day!

While ($true) {
    'Outer While loop'

    While ($true) {
        'Nested While loop'
        break outer
    }
}
'Outer While loop'
'Nested While loop'

PSMonday #42: February 13, 2017

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Topic: While

Notice: This post is a part of the PowerShell Monday series — a group of quick and easy to read mini lessons that briefly cover beginning and intermediate PowerShell topics. As a PowerShell enthusiast, this seemed like a beneficial way to ensure those around me at work were consistently learning new things about Windows PowerShell. At some point, I decided I would share these posts here, as well. Here’s the PowerShell Monday Table of Contents.

The last language construct we’re going to discuss is the While loop — yes, another looping construct. Let’s start with the help file in the first below command, followed by two ways to write the conceptual structure of the While loop.

Get-Help -Name about_While -ShowWindow

While (<condition>){<statement list>}

While (<condition>) {
     <statement list>
}

Our first below example of the While loop, well, it does absolutely nothing. We begin by setting our $Value variable to the numeric value of 1, and then we (attempt) to enter the While loop. The biggest difference between the While loop and the Do loop is that our conditions come before the statement lists. This should be reminiscent of the If, and Switch statement variations, where the evaluations come first.

$Value = 1

While ($Value -eq 5) {
    $Value
    $Value = $Value + 1
}

In the next example, we’ll make one simple change and the code will run. Our condition will evaluate the $Value variable such that it’s $true when $Value is less than or equal to 5. Remember from the For loop, that $Value++ is the same as writing $Value = $Value + 1.

$Value = 1

While ($Value -le 5) {
    $Value
    $Value++
}

1
2
3
4
5

Our final example for the While loop, gives the user an opportunity to try and guess a number between one and five. Before we potentially, enter the While construct, we’ll set the $MagicNumber variable to the random number and the $Continue variable to $true. We enter the While providing that $Continue is equal to $true, and we know it will be, as it was just assigned that value.

Inside the statement list, we (1) request the user enter a number between one and five, and (2) use and If-Else to see if the $MagicNumber matches the guess entered by the user, as stored in $Guess. If it matches, we indicate that, and then set $Continue to $false. This means that the next time the While begins, the condition won’t match and we won’t enter the While. The loop will be over. If $Guess and $MagicNumber don’t match, the While will execute again, and we’ll ask for another number.

$MagicNumber = Get-Random -Minimum 1 -Maximum 5
$Continue = $true

While ($Continue -eq $true) {
    $Guess = Read-Host "Enter the magic number"
    If ($Guess -eq $MagicNumber) {
        "You guessed it: $Guess <--> $MagicNumber"
        $Continue = $false

    } Else {
        Write-Output -InputObject 'Try again.'
    }
}

Enter the magic number: 5
Try again.
Enter the magic number: 4
Try again.
Enter the magic number: 2
Try again.
Enter the magic number: 3
You guessed it: 3 <--> 3

And, that’s it. We’ve seen and learned everything from If to Switch and For to While. As it was stated previously, knowing which language construct to use should be left to your intuition, and a full understanding of a language’s conditional options is the only way that’s going to happen. Next week we’ll start discussing reusable code.