$(変数名) = [int](文字列型の変数、値)
$(変換した値を格納する変数名) = [変換する型名](半関する変数、値)
$str1 = Read-Host "input1"
$str2 = Read-Host "input2"
$val1 = [int]$str1
$val2 = [int]$str2
$result = $val1 + $val2
Write-Output $result
$str1 = Read-Host "input1"
$str2 = Read-Host "input2"
$result = $str1 + $str2
Write-Output $result