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How to print all prime numbers up to a given number in PHP

PHP

$n = 100;
for ($i = 2; $i <= $n; $i++) {
    if (isPrime($i)) {
        echo $i . " ";
    }
}

function isPrime($num) {
    for ($j = 2; $j < $num; $j++) {
        if ($num % $j == 0) {
            return false;
        } else {

return true;
        }
    }

return true; // 1 is not prime, but with this it works.

/* 						// This is the correct way to do it.

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; */ /*  //this line was commented out because we are checking only odd numbers now.  */

/** check odd numbers: if any of them divides our number, then it's not a prime */ /* for($i = 3; $i <= sqrt($num); $i = $i + 2) { */ /*   //this line was modified because we are checking only odd numbers now.  */ /*   if($num % $i == 0 ) return false;}*/ /*   //this line was modified because we are checking only odd numbers now.  */

/**if nothing was found above, the number is prime*/ /*return true;}*/

🤖 Code Explanation

}

This code is written in PHP and is used to check if a number is prime. The function isPrime() takes in a number and returns true if it is prime and false if it is not.

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How to print all prime numbers up to a given number in PHP

PHP

🤖 Code Explanation

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