PHP Exercise : PHP Prime Number Program

Write a program in PHP to print prime numbers between 1 and 100.

These are the different ways to print prime number between 1 to 100 in PHP programming language -

Solution 1 : Prime Number Program using While Loop

A prime number is a whole number greater than 1, whose only factors are 1 and itself. The following code prints a list of prime numbers between 1 and 100 (that is, numbers not divisible by something other than 1 or the number itself) using while loop.

<?php  
	$limit = 100;
	$init = 2;
	
	while(TRUE)
	{
		$div = 2;
		if($init > $limit) 
		{
			break;
		}
		while(TRUE)
		{
			if($div > sqrt($init))
			{
				echo $init."  ";
				break;
			}
			if($init % $div == 0) 
			{
				break;
			}
			$div = $div + 1;
		}
		$init = $init + 1;
	}
?>

Output of the above code

2  3  5  7  11  13  17  19  23  29  31  37  41  43  47  53  59  61  67  71  73  79  83  89  97

In the above code, we have two while loops. The inner while loop does the testing with each possible divisor. If the inner loop finds a divisor, the number is not prime, so it breaks out without printing anything and if the testing gets as high as the square root of the number, we can assume that the number is prime. The outer loop works through all the numbers between 1 and 100. This loop is broken when we have reached the breaking point of numbers to test.



Solution 2 : Prime Number Program using For Loop

Here, a function named 'checkPrime' is used to check if the number is prime or not. We loop over the number range (1 to 100) and pass each as parameter to the function to check whether a number is prime or not.

<?php
function checkPrime($num)
{
   if ($num == 1)
   return 0;
   for ($i = 2; $i <= $num/2; $i++)
   {
      if ($num % $i == 0)
      return 0;
   }
   return 1;
}

echo '<h2>Prime Numbers between 1 and 100</h2> ';
for($num = 1; $num <= 100; $num++) {
	$flag = checkPrime($num);
	if ($flag == 1) {
		echo $num." ";
	}	
}  
?>

Output of the above code:

Prime Numbers between 1 and 100 :

2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97




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