Switch Parameter and an If Statement - powershell

Question

I am trying to use the value of a switch parameter as the trigger to write to a csv file if the parameter is called with the script from the command line. However, with my current code the csv file is created whether I include the parameter or not. What's up with that?
Also, is there a better way to handle my else/if else/if else section?
[CmdletBinding()]
param (
[Parameter(Mandatory=$true)]
[string]$dir,
[Parameter(Mandatory=$true)]
[int]$days,
[switch]$csv=$false
)
Process {
Clear-Host
$totSize = 0
$totFiles = 0
$modDate = (Get-date).AddDays(-$days).Date
$modfiles = Get-ChildItem -Path $dir -Recurse -ErrorAction SilentlyContinue | Where-Object { $_.LastWriteTime -ge $modDate }
If ($csv = $true){
$modfiles | Select-Object -Property FullName, Length,LastWriteTime | Export-Csv -Path .\modFiles.csv -NoTypeInformation
}
foreach ($file in $modfiles){
$totFiles = $totFiles + 1
$totSize = $totSize + $file.Length
}
If ($totSize -lt 1MB){
$outSize = $totSize/1KB
$unit = "KB"
}
elseif (($totSize -ge 1MB) -and ($totSize -lt 1GB)){
$outSize = $totSize/1MB
$unit = "MB"
}
elseif ($totSize -ge 1GB){
$outSize = $totSize/1GB
$unit = "GB"
}
$outRound = [math]::Round($outSize,2)
Write-Host $totFiles "Files"
Write-Host $outRound $unit
}

Answer 1

Two problems.
Do not specify a default value for a [switch] parameter. It will mess you up. Leave it off, and it will be $true if specified, and $false if
not.
When testing a logical value, such as an If statement, do not use the assignment equals (=), use the comparison equals (-eq).
If ($csv -eq $true){
$modfiles | Select-Object -Property FullName, Length,LastWriteTime | Export-Csv -Path .\modFiles.csv -NoTypeInformation
}
EDIT (Thanks #Scepticalist): Further, if the variable you are testing already holds a [bool] value, or can be implicitly converted to [bool], you don't even need the -eq $true part of the comparison, so:
If ($csv){
$modfiles | Select-Object -Property FullName, Length,LastWriteTime | Export-Csv -Path .\modFiles.csv -NoTypeInformation
}