PHP, MySQL, Drupal, .htaccess, Robots.txt, Phponwebsites: Find prime numbers between 1 and 100 in PHP

# Find prime numbers between 1 and 100 in PHP

This blog describes how to find prime numbers between 1 and 100 using PHP. Prime number is a number which is divided by 1 and itself.  Consider the number 5. It is prime number because it can be divided by 1 and 5.

### PHP program for prime numbers:

Consider the below program which is used to find prime numbers from 1 to 100.

<?php
for(\$i = 1; \$i <= 100; \$i++)
\$mm = 0;
for(\$j = 2; \$j <= \$i/2; \$j++) {
//only not prime numbers
if (\$i % \$j == 0) {
\$mm++;
break;
}
}
if (\$mm == 0) {
echo"\$i is prime number<br/>";
}
}
?>

In above program, if a number is divided by any number except 1 and itself, then it is not prime number. Otherwise it is a prime number.

Now you got prime numbers between 1 and 100 using PHP.
Related Post

#### 9 comments:

1. better optimisation is to search not to half of the number but to root of a number. There won't be any dividers later on

2. GMP gmp_nextprime ( int \$a )

3. Why not Sieve of Eratosthenes? It's more efficient:
http://www.hashbangcode.com/blog/sieve-eratosthenes-php

4. This comment has been removed by the author.

5. Much more efficient:

<?php

function is_prime(\$num)
{
\$max = (int)sqrt(\$num);
for(\$i = \$max; \$i >= 2; --\$i)
{
if (\$num % \$i == 0)
{
return false;
}
}
return true;
}

// The function returns the correct value,
// but skippig them will enable skipping even numbers
echo"1 is prime number<br>2 is prime number<br>";

for(\$i = 3; \$i <= 100; \$i+=2)
{
if (is_prime(\$i))
{
echo"\$i is prime number<br>";
}
}

6. 1 is neither prime nor composite.

7. opening brace missing after i loop!!!!