How to output prime numbers between 1 and 100 in PHP?

Here is a PHP code example for outputting all prime numbers between 1 and 100.

<?php
function is_prime($num) {
    if($num < 2) {
        return false;
    }
    for ($i = 2; $i <= sqrt($num); $i++) {
        if ($num % $i == 0) {
            return false;
        }
    }
    return true;
}

for ($i = 1; $i <= 100; $i++) {
    if (is_prime($i)) {
        echo $i . " ";
    }
}
?>

In the code above, we first define a function called is_prime to determine if a number is a prime number. We then use a loop to iterate through all numbers from 1 to 100, calling the is_prime function for each number. If it returns true, we output that number. The final output is all prime numbers between 1 and 100.