Printing prime numbers from an user's input php - php

Question

I'm trying ta make a program that will ask the user for a number and then show all the prime numbers between 0 to this number in an array.
<?php
class SmallerPrimes{
public function __construct($file){
$this->input_filename = $file;
}
public function Main(){
$smaller_than = (int)$this->readString()[0];
$result = array();
/* YOUR CODE HERE */
function isPrime($n)
{
if ($n <= 1)
return false;
for ($i = 2; $i < $n; $i++)
if ($n % $i == 0)
return false;
return true;
}
function printPrime($n)
{
for ($i = 2; $i <= $n; $i++)
{
if (isPrime($i))
echo $i . " ";
}
}
$n = 7;
printPrime($n);
/*end of your code here */
return $result;
}
public function readString(){
$file = fopen($this->input_filename, "r");
$line = array();
while (!feof($file)){
array_push($line, str_replace(PHP_EOL, "", fgets($file)));
}
return $line;
}
}
$o = new SmallerPrimes($argv[1]);
echo implode(" ", $o->Main()) . PHP_EOL;
This code work, but with a $n fixed.
I don't know how to use an input who ask the user a number
It's a code who verify itself and show us when it's ok
The code that i have to complete is this one (we only have this at first):
class SmallerPrimes{
public function __construct($file){
$this->input_filename = $file;
}
public function Main(){
$smaller_than = (int)$this->readString()[0];
$result = array();
/* YOUR CODE HERE */
return $result;
}
public function readString(){
$file = fopen($this->input_filename, "r");
$line = array();
while (!feof($file)){
array_push($line, str_replace(PHP_EOL, "", fgets($file)));
}
return $line;
}
}
$o = new SmallerPrimes($argv[1]);
echo implode(" ", $o->Main()) . PHP_EOL;

Answer 1

This is your script:
<?php
class SmallerPrimes{
public function __construct($file){
$this->input_filename = $file;
}
public function Main(){
$smaller_than = (int)$this->readString()[0];
$result = array();
function isPrime($n) {
if ($n <= 1) return false;
for ($i = 2; $i < $n; $i++) if ($n % $i == 0) return false;
return true;
}
function printPrime($n) {
for ($i = 2; $i < $n; $i++) if (isPrime($i)) $result[] = $i;
return $result;
}
$result = printPrime($smaller_than);
return $result;
}
public function readString(){
$file = fopen($this->input_filename, "r");
$line = array();
while (!feof($file)){
array_push($line, str_replace(PHP_EOL, "", fgets($file)));
}
return $line;
}}
$o = new SmallerPrimes($argv[1]);
echo implode(" ", $o->Main()) . PHP_EOL;

Answer 2

function getSmallerPrimes($smaller_than) {
if ($smaller_than <= 2) {
return [];
}
$result = [2];
$sqrt = sqrt($smaller_than);
for ($n = 3; $n < $smaller_than; $n += 2) {
$isPrime = true;
foreach($result as $prime) {
if ($n % $prime == 0) {
$isPrime = false;
break;
}
if ($prime > $sqrt) {
break;
}
}
if ($isPrime) {
$result[] = $n;
}
}
return $result;
}
$input = 23;
echo implode(' ', getSmallerPrimes($input));
Result: 2 3 5 7 11 13 17 19