检测输入是否是PHP中的素数 - 关注最佳实践代码语法[重复]

Question

This question already has an answer here:

• A formula to find prime numbers in a loop 20 answers

I'm teaching my wife to code, so we made a simple prime-number detector.

We came up with this, but I'm wondering if there's a better / neater way. I particularly don't like the 0/1 switch for displaying the end statement.

//get n from URL
$n = $_GET['n'];

$j=2;
$prime=1;

while ($j<=($n/2)){

    if (is_int($n/$j)){ $prime=0;
        break;
    }

   $j++;

}

if ($prime==1) {echo "Yes! $n is a prime number";}
else {echo "No, $n is not a prime number";}

</div>

Answer 1

There is always the neat and newbie friendly regular expressions way of finding prime numbers:

$n = $_GET['n'];
echo "$n is ", preg_match('/^1?$|^(11+?)\1+$/', str_repeat('1', $n))
    ? "not " : "", "a prime number", PHP_EOL;

No seriously, what I would suggest is that you tidy up your code a bit, so it gets easier to read:

• Remove unnecessary parentheses
• Rename $prime to $isPrime
• Change $j++ into $j = $j + 1
• Add a quick check on 0, 1 which are not prime numbers

Like so:

// Get parameter 'n' from URL
$n = $_GET['n'];

if ($n <= 1) {
    $isPrime = false;
}
else {
    $isPrime = true;
    $j = 2;

    while ($j <= $n / 2) {
        if (is_int($n / $j)) {
            $isPrime = false;
            break;
        }
        $j = $j + 1;
    }
}

if ($isPrime) {
    echo "$n is a prime number";
}
else {
    echo "$n is not a prime number";
}