w3resource
php Programming Exercies

PHP Exercises: Print the number of prime numbers which are less than or equal to a given integer

PHP: Exercise-52 with Solution

Write a PHP program to print the number of prime numbers which are less than or equal to a given integer.

Input:
n (1 ≤ n ≤ 999,999) .

Pictorial Presentation:

PHP: Print the number of prime numbers which are less than or equal to a given integer.

Sample Solution: -

PHP Code:

<?php

$a = array_fill(0, 1000000, true);
$a[0] = $a[1] = false;
 
for($i = 2; $i * $i < 1000000; $i++){
    if(!$a[$i]) continue;
    for($j = $i * $i; $j < 1000000; $j += $i){
        $a[$j] = false;
    }
}
 
$sum = array_fill(0, 1000000, 0);
 
for($i = 1; $i < 1000000; $i++){
    $sum[$i] += $sum[$i - 1];
    if($a[$i]) $sum[$i]++;
}
 
while(fscanf(STDIN, "%d", $n)){
    echo "Number of prime numbers which are less than or equal to n: ";
    echo $sum[$n] . "\n";
}
?>

Sample Output:

Sample Input: 50
Number of prime numbers which are less than or equal to n: 15

Flowchart:

Flowchart: Print the number of prime numbers which are less than or equal to a given integer.

PHP Code Editor:

Have another way to solve this solution? Contribute your code (and comments) through Disqus.

Previous: Write a PHP program to compute the amount of the debt in n months.
Next: Write a PHP program to compute the radius and the central coordinate (x, y) of a circle which is constructed by three given points on the plane surface.

What is the difficulty level of this exercise?