Number of primes between two numbers

Created:05 Apr 2017 10:53:55 , in  Maths

A script for finding all the primes there are between two given numbers.

Primes class

/* Class: Primes - find whether number is a prime or find all primes between a pair of numbers
   Author : Sylwester Wojnowski
   WWW : wojnowski.net.pl
    
   Methods: 
     public is_prime($a)
       Description:
         check for primality of $a  
       Parameters: 
         $a positive integer
       Return Value:
         bool - true,false
         
    public find_primes($b, $a=1, $inclusive = true)
       Description:
         find primes between $a and $b
       Parameters: 
         $b positive integer
         $a positive integer - optional - default 1
         $inclusive bool - optional - default true
           if false, $a and $b will not be included in the computation
       Return Value:
         array - array of numbers         
*/

class Primes{
  private $primes = array();
   
  public function __construct(){}
  
  # find factors of number a
  private function factors($a){
    $factors = array();
    $n = 1;
    
    if(!is_int($a)){
      return $factors;
    }
    
    while($n <= $a){
      $b = $a / $n;
      
      if(is_int($b)){
        $factors[] = $b;
      }
      
      $n++;
    }
    
    return $factors;
  }
  
  # find out whether $a is a prime
  public function is_prime($a){
    return count($this -> factors($a)) == 2 ? true : false;  
  }
  
  # find primes between numbers b and a
  public function find_primes($b,$a = 1 , $inclusive = true){
     
    $this -> primes = array();     
        
    if(!$inclusive){
      $a++;
      $b--;
    }
    
    if($a < 1 || $b < 1 || $a > $b ){
      return array();
    }
  
    while($a <= $b){
    
      if($this -> is_prime($a)){
        $this -> primes[] = $a;
      }
 
      $a++;
    }
      
    return $this -> primes;
  }
}

Finding your primes using Primes

Finding out if 37 is a prime:

$pr = new Primes();
$pr->is_prime(37);

Finding all the primes up to 13 inclusive:

$pr->find_primes(13);

Finding all the primes between 90 and 120 inclusive:

        
$pr->find_primes(120,90);

Finding all the primes between 3 and 119 inclusive:

$pr->find_primes(120,2,false);

Finding all the primes less than 120:

    
$pr->find_primes(120,0,false);

This post was updated on 06 Oct 2021 21:25:41

Tags:  php