Type conversion problem in a PowerShell function

Question

I am very new to PowerShell scripting and was experimenting with Function. This is the code I wrote:

Function Add
{
   $sum = 0;
   for($i = 0; $i -le $args.length; ++$i)
   {
     [int] $num = $args[$i]
     $sum += $num
   }
   Write-Output "Sum is $sum"
}

And I tried to call using Add 1,2,3. However, when I execute I get the following error:

Cannot convert the "System.Object[]" value of type "System.Object[]" to type "System.Int32".

Any idea how to fix this?

ggorlen · Accepted Answer · 2023-02-20 06:31:46Z

33

There's a bg trap in Powershell: , is the array operator. Try this at the command line:

PS> 1,2,3

You'll see that it's an array:

PS> (1,2,3).gettype()
IsPublic IsSerial Name                                     BaseType
-------- -------- ----                                     --------
True     True     Object[]                                 System.Array

Try to call Add without commas:

PS> Add 1 2 3
Sum is 6

Don't forget everything is an object in Powershell. You are playing on top of .NET.

So you have two friends:

The gettype() method which gives you the type of an object
The Get-Member CmdLet which helps you on properties and methods of an object

Get-member has many parameters that can help.

edited Feb 20, 2023 at 6:31

ggorlen

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answered May 15, 2011 at 6:58

JPBlanc

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1 Comment

Naveen Over a year ago

Thanks..I am from C++ background and didn't think twice before calling function with parameter separated by ,

Emiliano Poggi · Accepted Answer · 2011-05-15 07:15:27Z

5

Casting is normally performed assign the type at the right hand side:

$num = [int] $args[$i]

Could be this your problem?

Second observation:

As @JPBlanc has observed, you are passing an array to your function, not three parameters. Use:

Add 1 2 3

and you will get it. Anyway, you don't need casting in this situation. May be in this:

Add "1" "2" "3"

Obviously you can keep calling your function like Add 1,2,3, but you need to change it as follows:

Function Add {
   args[0] | % {$sum=0}{$sum+=$_}{write-output "Sum is $sum"}
}

edited May 15, 2011 at 7:15

answered May 15, 2011 at 7:02

Emiliano Poggi

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3 Comments

JPBlanc Over a year ago

Look a bit more Empo @Naveen made a newby error he tried to call with an array as parameter in spite of passing parameters.

JPBlanc Over a year ago

You'll still need "," when you call object methods with parameters. It's really a trap in powershell newby or coming from any langue.

Emiliano Poggi Over a year ago

Yes, that's true. You call object methods with arguments (if any), in the common way, with commas, as you'll do in C#. You call cmdlets with parameters without commas.

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