Check if a number is prime Using powershell

Question

This is my script to check if a random number is prime or not :

[int]$nombre = Get-Random -Minimum 1 -Maximum 10
$nombre
$j=0

if($nombre -lt 2) { " $nombre n'est pas premier " }

else {

for($i=1; $i -le $nombre; $i++){

if( $nombre%$i -eq 0) {$j++}

 }
 if($j -eq 2 ) { "Le nombre est  premier "}
 else {"Ce nombre est premier"}
   } 

When I execute the script I get wrong results like 4 is a prime number. Any ideas to fixe it ? Thank you

Answer 1

I just wanted to improve the existing answer.

To me it is so obvious that I don't understand why hasn't anyone pointed out, it could simplify the whole process by skipping the for loop if the number is a square number, just add if ([math]::Sqrt{$number} -is [int]) {$prime = $false} to the code before the loop, by definition square numbers are composite numbers, why no one noticed it?

Update: a better function based on the previous answer, it assigns $false to negative numbers, zero and fractions and non-numbers:

function Test-Prime {
    param(
    [Parameter(ValueFromPipeline=$true)]
    $number
    )
    
   Process {
    $prime = $true;
    if ($number -isnot [int]) {$prime = $false}
    elseif ($number -le 0) {$prime = $false}
    else {
        if ($number -eq 1) {
            $prime = $false;
        }
        if ($number -gt 3) {
            $sqrt = [math]::Sqrt($number); 
            if ($sqrt -is [int]) {$prime = $false}
            else {
                for($i = 2; $i -le $sqrt; $i++) {
                    if ($number % $i -eq 0) {
                        $prime = $false;
                        break;
                    }
                }
            }
        }
    }
    return $prime;
}

}