I don't understand why pressing enter key is the same as pressing 0 on the keyboard.
[int] $Choice = -1
$Count = 2
while ($Choice -lt 0 -or $Choice -gt $Count)
{
Write-Host "Input number"
$Choice = Read-Host
Write-Host "choice:"
Write-Host $Choice
}
The output will be 0 even if just press enter. I want the user to explicitly input 0.
In the very first statement:
[int] $Choice = -1
... you type-cast $choice to [int].
When you apply a cast to the left-hand side of an assignment (to the left of the variable name), PowerShell will "remember" it as a type-constraint and treat the variable as strongly typed - PowerShell will attempt to convert anything you assign to $choice from there on out to an [int].
Hitting enter in the prompt without any other input results in Read-Host returning an empty string (like "")
The conversion logic treats the empty string as $null, and casting $null to [int] results in the value 0. You can see this by casting an empty string to [int] directly:
PS C:\> [int]""
0
You should probably validate the input from Read-Host before assigning to $Choice if you explicitly require a number:
$inputString = Read-Host
if($inputString -notmatch '^\d+$') {
Write-Host "Digits only please!"
continue
}
Related
I have this piece of code in PowerShell. I need user input validation to integer with writing output saying what is wrong with the input and expecting correct input.
$FromObj = "Please input object number"
$FromInput = Read-Host $FromObj
while(($FromInput -isnot [int])) {
#I also want to put in the while that the input has to be an integer, -gt 0, and -lt 800
Write-Output "Your input has to be a number."
$FromInput = Read-Host $FromObj
}
if ($FromInput -le 0) {
Write-Output "Your input has to be a number greater than 0!"
$FromInput = Read-Host $FromObj
}
elseif ($FromInput -ge 800) {
Write-Output "Your input has to be a number less than 800!"
$FromInput = Read-Host $FromObj
}
else {
$FromInput = $FromInput -as [int]
}
However, this is not working for me. Could you help me with validating it with writing outputs as the ones displayed above?
I think Nicks's link in comment already provides different right answers to your question i.e.: using regex to match \d+ (digits) or using [int]::TryParse(...) but to explain why your code is not working:
Read-Host will store user input as string unless you manipulate it which is what you were already doing on your last condition (the else {...} statement).
This is why you never get past the $FromInput -isnot [int] condition.
To fix the code you could simply attempt to store user input -as [int] since the beginning and since you have 3 Read-Host on your code you could save the user input attempt -as [int] in a ScriptBlock which then can be easily executed as many times as needed:
$FromObj = "Please input object number"
$giveMeNumber = { (Read-Host $FromObj) -as [int] }
$FromInput = & $giveMeNumber
while($FromInput -isnot [int]) {
Write-Output "Your input has to be a number."
$FromInput = & $giveMeNumber
}
if ($FromInput -le 0) {
Write-Output "Your input has to be a number greater than 0!"
$FromInput = & $giveMeNumber
}
elseif ($FromInput -ge 800) {
Write-Output "Your input has to be a number less than 800!"
$FromInput = & $giveMeNumber
}
Note, even though this works, the statement is not entirely correct since you're breaking out of the while loop after the input is [int] the user could force an incorrect input.
Try this instead which will execute indefinitely until right input:
Clear-Host
$ErrorActionPreference = 'Stop'
$FromObj = "Please input object number"
$scriptBlock = {
try
{
$FromInput = [int](Read-Host $FromObj)
# Note I'm using Write-Host instead of Write-Ouput, this is because
# we don't want to store the invalid inputs messages in the
# $userInput variable.
if ($FromInput -le 0) {
Write-Host "Your input has to be a number greater than 0!"
& $scriptBlock
}
elseif ($FromInput -ge 800) {
Write-Host "Your input has to be a number less than 800!"
& $scriptBlock
}
else {
$FromInput
}
}
catch
{
Write-Host "Your input has to be a number."
& $scriptBlock
}
}
$userInput = & $scriptBlock
I need to in powershell
-Ask the user for a 2-digit number
-Validate this number is two numeric digits
-Take into account leading zeroes
-If the number is invalid, have the user try again
It seemed that using
$2digit = read-host
$2digit -match "[0-9][0-9]"
was working but it stopped out of nowhere. Any advice?
You are probably getting an a false result when you entered more than 2 characters.
eg:
This is because you have not specified length.
Resolution:
$2digit = read-host
($2digit.Length -le 2) -and ($2digit -match "[0-9][0-9]")
You can also change your regex pattern
$2digits -match "^[0-9][0-9]$"
^ - start of string or line
$ - end of string or line
I was able to figure it out
do{
do {
write-host -nonewline "Enter the two digit number: "
$2d = read-host
$value = $2d -as [Double]
$ok = $value -ne $NULL
if ( -not $ok ) { write-host "!!ERROR:You must enter numeric values!!" }
}
until ( $ok )
if ($2d.Length -eq 2){$holder = $true}
elseif($2d.Length -ne 2){Write-host "!!ERROR:The number must be 2 digits!!"}
}
while ( $holder -ne $true )
The first do loop will verify that the input is numeric and the second do loop will check it to be 2 numbers.
Regular expressions are your friend. This will only accept digits 0-9 with a length of two. Anything else will not be accepted.
do {
$input = Read-Host -Prompt 'Enter the two digit number(0-9)'
if ( $input -match '^\d{2}$' ) {
break
}
Write-Host "The value must be a two digit number; $input is invalid"
} while ( $true )
What exactly am I doing wrong here, it seems to be subtracting just fine but adding and multiplying seems to not work at all.
How do I get it to do the calculations correct and allow the if statement to also work as it seems to always run even if the numbers are incorrect size.
$a = Read-Host "What is your name?"
$b = Read-Host "Enter a 2 digit number"
$c = Read-Host "Enter a 3 digit number"
if (($b -ge 10) -and ($b -le 99) -and ($c -ge 100) -and ($c -le 999)){
$d = $b + $c
$e = $b * $c
$g = $b - $c
$d
$e
$g
Write-host "Here you go $a"
}
else {
write-host "Enter the numbers correctly"
}
Here the results I get
Read-Host always outputs a string.
In order to treat the output as a number, you must explicitly convert it to one:
$a = Read-Host "What is your name?"
# Note: Add error handling with try / catch
# and a retry loop to deal with invalid input.
[int] $b = Read-Host "Enter a 2 digit number"
[int] $c = Read-Host "Enter a 3 digit number"
The above type-constrains variables $b and $c to integer values (by placing the [int] cast to the left of the target variable in the assignment), which automatically converts Read-Host's [string] output to [int].
To spell it out with a concrete example that prompts until a two-digit (decimal) number is entered:
do {
try {
[int] $b = Read-Host "Enter a 2 digit number"
} catch {
continue # Not a number - stay in the loop to prompt again.
}
if ($b -ge 10 -and $b -le 99) { break } # OK, exit the loop.
} while ($true)
Note: Strictly speaking, the [int] cast accepts anything that would work as a number literal in PowerShell, which includes hexadecimal representations, such as 0xA, as well as number with a type suffix, such as 10l - see this answer for more information.
As for what you tried:
Except for -, all the operators used in your code have string-specific overloads (meaning); note that it is sufficient for the LHS to be of type [string] to trigger this behavior.[1]
-lt / -ge perform lexical comparison with strings; e.g., '10' -gt '2' yields $false, because, in lexical sorting, string '10' comes before string '2'.
-and / -or treat empty strings as $false, and any nonempty string as $true; e.g., '0' -and '0' is $true, because '0' is a nonempty string.
+ performs string concatenation; e.g., '1' + '0' is '10'.
* performs string replication; e.g., '1' * 3 is '111' - the LHS is repeated as many times as specified by the number on the RHS; note that '1' * '3' works the same, because the RHS is coerced to an [int] in this case.
- is the only exception: it always performs a numeric operation, if possible; e.g, '10' - '2' yields 8, because both operands were implicitly converted to [int]s.
[1] Typically, it is the LHS of an operation that determines its data type, causing the RHS to be coerced to a matching type, if necessary.
This should be really simple, but I cannot make it work. I'm new to the PowerShell so my mistake is probably obvious. I'm trying to ask a user for an input using a while loop, and prompting the user to try again if what was entered was not numeric. In bash it would look like this:
while read -p "What is the first number? " first; do
if [[ $first = *[[:digit:]]* ]]; then
break # if $first is numeric, break loop
else
echo "$first is not numeric. Enter a numeric value. "
fi
done
Here's what I have for the PS:
While ($first = (Read-Host "What is the first number?") -as [double]) {
if ($first -eq $null) { Write-Host "Please enter a numeric value." }
else { break }
}
In the example above, I can break the loop fine when a number is entered, but I can't see the Write-Host statement if I type a string.
Looking at the While line:
While ($first = (Read-Host "What is the first number?") -as [double])
This will only enter/continue the loop body when the input is already a double, because it rolls up the cast to double as part of the loop condition. You want to enter the loop body on any input, and only check if it's a double afterwards. At least, that's what the bash code does:
While ($first = (Read-Host "What is the first number?")) {
if ( ($first -as [double]) -eq $null) { Write-Host "Please enter a numeric value." }
else { break }
}
Or you could continue using the cast as part of the condition by negating the whole expression, and thus avoid the need for the awkward break:
While (-not ($first = (Read-Host "What is the first number?") -as [double])) {
Write-Host "Please enter a numeric value."
}
You could use this to keep prompting for a valid number input as you are looking for.
Do {
"Please enter a numeric value." | Out-Host
$first = (Read-Host "What is the first number?") -as [double]
} While($null -eq $first)
I am new to powershell and trying to learn loops but i'm currently confused and stuck trying to create a while and until loop that,Asks input from the user, Allow input until a sentinel value is reached, Count the number of times the loop went thru, print out the user input onto new lines, then print the loop number.
while ($UserNumber = Read-Host -Prompt "Input a number from 1 to 10" )
echo "You have entered $UserNumber, now it will count until 20."
This is only the start and I have no idea how to continue. Any and all help would be greatly appreciated.
This may help
$loopCount = 0
do{
$answer = Read-Host "Input a number 1 - 10"
Write-Host "You entered $answer"
$loopCount++
if($answer -eq 4){
$answered = $true
}
} until ($answered -eq $true)
Write-Host ("Looped {0} times" -f $loopCount)
What's in your while (or until) statement needs to result in a boolean value, much like an if statement.
What you're likely going to want to do here is first ask the user for a number:
[int] $UserNumber = Read-Host -Prompt "Input a number from 1 to 10"
Write-Host "You have entered $UserNumber, now it will count until 20."
Note that I've specified that the $UserNumber is an integer... this is to stop PowerShell treating it as a string, which it would be default.
Then you'll want to construct a loop that runs while a certain condition is true (I'm assuming that the number is "less than 20" is what you're thinking about here.)
while ($UserNumber -lt 20) {
$UserNumber += 1 # Increase the value stored in the variable by 1.
$UserNumber
}
That loop will continue, incrementing that number by one (and output it) each iteration, until it reaches 20 or higher. The last time it is output, it will display "20".
$num=0
$total=0
$counter=0
do
{
$num = Read-Host " Input Number"
$total=$total + $num
$counter++
Echo "Counter : $counter and Total : $total"
}
until($total -ge 20 -or $counter -eq 10)
Write-Host "Output : $total and Number Input : $counter"
Results