## Thursday, 27 January 2011

### Calculate prime numbers using PHP

Simply create a file named primeNumberCalculator.php. Copy following text in it.

You need a web server supporting php scripting.
Place the file where your http web server see it. e.g: /var/www

Open the file in a web browser. e.g: http://localhost/primeNumberCalculator.php

```<html>
<body>

<h2>PHP Prime number calculator</h2>
How many primes?: <input type="text" name="count" />
<input type="submit" value="Submit" />
</form>
<?php

// How many prime numbers are we going to calculate:
\$count=\$_GET["count"];
if (\$count == "") {
\$count = 10;  // Default value
}

// We show the first prime number:
\$prime_array=array("2");
echo \$prime_array[0];
echo " ";

\$total=1; // prime number array length.
\$number = 3; // current number we are going to test for primality.

while ( \$i<\$count ) {
\$index=0;
\$is_prime="true";
\$max = floor(sqrt(\$number));
\$n = \$prime_array[\$index];
while((\$n <= \$max) && (\$is_prime == "true")) {
if ((\$number % \$n) == 0) {
\$is_prime="false";
}
\$index++;
\$n = \$prime_array[\$index];
}
if (\$is_prime=="true") {
echo " " . \$number;
\$prime_array[\$total] = \$number;
\$total++;
\$i++;
}

\$number += 2;
}

?>

</body>
</html>
```

## Wednesday, 12 January 2011

### Calculate a PRIME NUMBER list using JAVA

This article shows how to write, compile, build and execute a program that calculates a list containing the first prime numbers using Java language.

We are going to create a source code file named CalculatePrimeNumbers.java
Then we copy/paste next programm in that file.

NOTE: Name is important, because in Java language file name has to match the class it contains.

```import java.util.ArrayList;

/**
*/

// By default it shows 50 first prime numbers.
private static final int MAX_PRIMES = 50;

/**
* @param args the command line arguments
* This function accepts zero or one arguments.
* When called with no arguments it shows 50 first prime numbers.
* If we specify a number, it shows that a prime number array with that specified length.
*/
public static void main(String[] args) {
int top;

// Parse command line arguments.
switch(args.length){
case 0:
top = MAX_PRIMES;
break;
case 1:
top = Integer.parseInt(args[0]);
break;
default:
System.err.println("ERROR: TOO MANY ARGUMENTS.");
return;
}
System.out.println("We are going to calculate " + top + " first prime numbers.");

ArrayList<long> primes = new ArrayList<long>();
primes.add(2L); // 2 is the first prime number we get.
long index = 3; // Calculations start for number 3.

System.out.println("Prime number list:");
System.out.print(2 + " ");
while (primes.size() < top) {
boolean isPrime = true;

for(long n:primes) {
if ((index % n) == 0) {
isPrime = false;
break;
}
} // End for.

if (isPrime) {
// index stores a prime number.