我需要使用for循环或while循环查找素数
我写了这个，但这是错误的
<?php $i = 1; while($i<5) { for($j=1; $j<=$i; $j++) { if ($j != 1 && $j != $i) { echo $i . "/" . $j . "=" . $i%$j . "<br />"; if ($i%$j != 0) { echo $i . "<br />"; } } } echo "<br />"; $i += 1; } ?>
有没有一种方法可以将数字与数组相除以找到余数？
这是我发现的一个小功能：（http://icdif.com/computing/2011/09/15/check-number-prime- number/）似乎对我有用！
function isPrime($num) { //1 is not prime. See: http://en.wikipedia.org/wiki/Prime_number#Primality_of_one if($num == 1) return false; //2 is prime (the only even number that is prime) if($num == 2) return true; /** * if the number is divisible by two, then it's not prime and it's no longer * needed to check other even numbers */ if($num % 2 == 0) { return false; } /** * Checks the odd numbers. If any of them is a factor, then it returns false. * The sqrt can be an aproximation, hence just for the sake of * security, one rounds it to the next highest integer value. */ $ceil = ceil(sqrt($num)); for($i = 3; $i <= $ceil; $i = $i + 2) { if($num % $i == 0) return false; } return true; }
