PHP function that finds all prime numbers within a given range | Nested for loop

In this video, we are going to learn how to find all prime numbers within a given range. For those who don’t know, a prime number is an integer that only has two divisors, namely 1 and the integer itself, e.g.

1 x 7 = 7
1 x 11 = 11
1 x 23 = 23
1 x 37 = 37
1 x 41 = 41
1 x 53 = 53

In order to find all prime numbers within a given range, we need a PHP function. We will call this function find_prime_numbers(). Because there are infinitely many prime numbers, the function must be given a specific range within which to search for prime numbers. Thus, the first argument of the function is the lower limit of the range. Its default value is 1. The second argument of the function is the upper limit of the range. Its default value is 1000. And the output of the function is an array that contains all prime numbers from within the given range.

First, we declare the array that is going to store all prime numbers. Then, we use a nested for loop, i.e. a for loop inside another for loop. We use the outer for loop to loop through the range of numbers, and the inner for loop to find the divisors of each number within the range. If a number only has two divisors, namely 1 and itself, then that number is a prime number. Finally, we build up the array that is going to store all prime numbers within the range, and return it.

Further links
PHP function that finds all divisors of a number: https://youtu.be/g0x2OTujpZo

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Disclaimer: this video is meant to be a proof of concept.