PHP Exercises: Compute the sum of first n given prime numbers

Last update on May 30 2022 11:44:53 (UTC/GMT +8 hours)

PHP: Exercise-65 with Solution

Write a PHP program to compute the sum of first n given prime numbers.

Input: n ( n ≤ 10000). Input 0 to exit the program.

Pictorial Presentation:

PHP: Compute the sum of first n given prime numbers.

Sample Solution: -

PHP Code:

<?php
$max = 105000;
$arr = new \SplFixedArray($max + 1);
for ($i = 2; $i <= $max; $i++) {
    $arr[$i] = 1;
}
for ($i = 2, $len = sqrt($max); $i <= $len; $i++) {
    if (!$arr[$i]) {
        continue;
    }
    for ($j = $i, $len2 = $max / $i; $j <= $len2; $j++) {
        $arr[$i * $j] = 0;
    }
} 
while (($line = trim(fgets(STDIN))) !== '0') {
    $n = (int)$line;
    $result = 0;
    $cnt = 0;
    for ($i = 2; $i <= $max; $i++) {
        if ($cnt === $n) {
            break;
        } elseif ($arr[$i]) {
            $result += $i;
            $cnt++;
        }
    }
    echo "Sum of first ".$n." prime numbers:";
    echo $result, PHP_EOL;
}
?>

Sample Input:
25
0

Sample Output:

Sum of first 25 prime numbers:1060

Flowchart:

PHP Code Editor:

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Previous: Write a PHP program to replace a string "Python" with "PHP" and "Python" with " PHP" in a given string.
Next: Write a PHP program that accept a even number (n should be greater than or equal to 4 and less than or equal to 50000, Goldbach number) from the user and create a combinations that express the given number as a sum of two prime numbers. Print the number of combinations.

What is the difficulty level of this exercise?

Test your Programming skills with w3resource's quiz.

PHP: Tips of the Day

How to Sort Multi-dimensional Array by Value?

Try a usort, If you are still on PHP 5.2 or earlier, you'll have to define a sorting function first:

Example:

function sortByOrder($a, $b) {
    return $a['order'] - $b['order'];
}

usort($myArray, 'sortByOrder');

Starting in PHP 5.3, you can use an anonymous function:

usort($myArray, function($a, $b) {
    return $a['order'] - $b['order'];
});

And finally with PHP 7 you can use the spaceship operator:

usort($myArray, function($a, $b) {
    return $a['order'] <=> $b['order'];
});

To extend this to multi-dimensional sorting, reference the second/third sorting elements if the first is zero - best explained below. You can also use this for sorting on sub-elements.

usort($myArray, function($a, $b) {
    $retval = $a['order'] <=> $b['order'];
    if ($retval == 0) {
        $retval = $a['suborder'] <=> $b['suborder'];
        if ($retval == 0) {
            $retval = $a['details']['subsuborder'] <=> $b['details']['subsuborder'];
        }
    }
    return $retval;
});

If you need to retain key associations, use uasort() - see comparison of array sorting functions in the manual

Ref : https://bit.ly/3i77vCC