How to check if a number is prime?

Question: What is Prime Number
A prime number is a natural number greater than 1 that cannot be formed by multiplying two smaller natural numbers.


Question: Give the example of Prime Number
2, 3, 5, 7, 11, 13, 17, 19, 23 and 29.


Question: Write an function that check the prime number OR Not?

function checkPrime($number){
    if($number < 0 ){
        return false;
    }
    $return=true;
    for($i=2; $i < $number; $i++){
        if($number % $i ==0){
            $return=false;
            break;
        }
    }
   return $return;
}

Question: How to check a number is prime Or Not?

echo checkPrime(2)?'Prime':'Not Prime'; //Prime
echo checkPrime(4)?'Prime':'Not Prime'; //Not Prime
echo checkPrime(6)?'Prime':'Not Prime'; //Not prime
echo checkPrime(7)?'Prime':'Not Prime';  //Prime

Question: What are the prime numbers between 1 to 100?

for( $i = 2; $i < 100; $i++ ){
    if( checkPrime( $i ) ){
        echo $i;
        echo ',';
    }
}