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:

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:

PHP Code Editor:
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PHP: Tips of the Day
Mutates the original array to filter out the values specified
Example:
<?php function tips_pull(&$items, ...$params) { $items = array_values(array_diff($items, $params)); return $items; } $items = ['x', 'y', 'z', 'x', 'y', 'z']; print_r(tips_pull($items, 'y', 'z')); ?>
Output:
Array ( [0] => x [1] => x )
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