PHP function Exercises: Check whether a number is prime or not

Last update on May 31 2025 12:57:44 (UTC/GMT +8 hours)

2. Prime Number Checker

Write a PHP function to check whether a number is prime or not.

Note: A prime number (or a prime) is a natural number greater than 1 that has no positive divisors other than 1 and itself.

Visual Presentation:

PHP function Exercises: Check whether a number is prime or not

Sample Solution:

PHP Code:

<?php
// Function to check if a number is prime
function IsPrime($n)
{
    // Loop through all numbers from 2 to n-1
    for ($x = 2; $x < $n; $x++)
    {
        // If n is divisible by any number other than 1 and itself,
        // it's not prime, so return 0
        if ($n % $x == 0)
        {
            return 0;
        }
    }
    // If no divisor found, n is prime, so return 1
    return 1;
}

// Call the IsPrime function to check if 3 is prime
$a = IsPrime(3);

// Check the return value and print the result
if ($a == 0)
    echo 'This is not a Prime Number.....' . "\n";
else
    echo 'This is a Prime Number..' . "\n";
?>

Output:

This is a Prime Number..

Explanation:

In the exercise above,

Define a function named "IsPrime()" which takes an integer parameter '$n'.
Inside the function, there's a loop that iterates from 2 to one less than '$n'. This loop checks for divisors of '$n'.
If '$n' is divisible by any number other than 1 and itself, the function returns 0, indicating that the number is not prime.
If no divisor is found in the loop, the function returns 1, indicating that the number is prime.
Outside the function, the "IsPrime()" function is called with an argument of 3, and the result is stored in the variable '$a'.
The code then checks the value of '$a' and prints whether 3 is a prime number or not.

Flowchart :

For more Practice: Solve these Related Problems:

Write a PHP function to determine if a number is prime by checking divisibility only up to the square root of the number.
Write a PHP script that uses a for loop to test for prime numbers and returns an array of all primes within a given range.
Write a PHP function to check for primality using recursion and memoization to optimize repeated checks for multiple inputs.
Write a PHP program to implement the Sieve of Eratosthenes algorithm and compare its performance with a basic loop-based prime checker.

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PHP Code Editor:

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