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

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:

Sample Solution:

PHP Code:

<?php
// Set the maximum value for prime numbers
$max = 105000;

// Create a fixed-size array to store prime flags
$arr = new \SplFixedArray($max + 1);

// Initialize the array with 1 (considering all numbers as prime initially)
for ($i = 2; $i <= $max; $i++) {
    $arr[$i] = 1;
}

// Sieve of Eratosthenes algorithm to mark non-prime numbers
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;
    }
} 

// Process input until '0' is entered
while (($line = trim(fgets(STDIN))) !== '0') {
    // Convert the input to an integer
    $n = (int)$line;

    // Initialize variables for result and count
    $result = 0;
    $cnt = 0;

    // Find and sum the first N prime numbers
    for ($i = 2; $i <= $max; $i++) {
        if ($cnt === $n) {
            break;
        } elseif ($arr[$i]) {
            $result += $i;
            $cnt++;
        }
    }

    // Output the result
    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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