This is java program implements the psuedo-random number generator: X(n+1) = (7^5 * X(n)) mod(2^31 - 1) to approximate the value of pi

PRNG.java

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;


public class PRNG {
	private long seed = 0;
	private final long	mod = Integer.MAX_VALUE,
				seven_pow = (long)Math.pow(7, 5);
	
	/**	Creates a PRNG with the seed x0 */
	public PRNG(int x0){
		//	Convert x0 to positive nonzero equivalent form
		if(x0 <= 0)
			while(x0 <= 0)
				x0 += 10;
			
		seed = (seven_pow * x0) % mod;	
	}
	
	/**	Return the next random number */
	public int next_rand(){
		int this_rand = (int)seed;
		//	Set next random number
		seed = (seven_pow  * seed) % mod;
		return this_rand;
	}
	
	/** Returns the greatest common denominator **/
	private int gcd(int x, int y){
		if(x < 0)
			while(x < 0)
				x += 10;
		
		if(y < 0)
			while(y < 0)
				y += 10;
	
		return (y == 0 ? x: gcd(y, x % y));
	}
	
	/**	Returns an approximation of Pi */
	public double approximate_pi(int n){
		if(n < 0)
			while(n < 0)
				n += 10;
		
		int 	x = next_rand(),
				y = next_rand(),
				relative_prime_count = 0, // aka rpc
				gcd = 0;
		double pi = -1; // will hold the approximation, returns -1 if rpc <= 0
		
		//	count the number of random relatively prime integers in 'n' iterations
		for(int i = 0; i < n; i++){
			gcd = gcd(x, y);
			// increment rpc if two psuedo-random integers are relatively prime
			relative_prime_count = (gcd == 1 ? relative_prime_count + 1 : relative_prime_count + 0);
			x = next_rand();
			y = next_rand();
		}
		pi = (relative_prime_count > 0 ? Math.sqrt(6 * n / (double) relative_prime_count) : pi);
		return pi;
	}
	
	public static void main(String[] args){
		System.out.print("Enter the seed: ");
		try{
		    BufferedReader bufferRead = new BufferedReader(new InputStreamReader(System.in));
		    //	Get seed
		    String s = bufferRead.readLine();
		    PRNG rand = new PRNG(Integer.parseInt(s));
		    
		    System.out.print("Enter number of iterations: ");
		    //	Get the number of iterations
		    s = bufferRead.readLine();
		    System.out.println("Approximation of Pi: " + rand.approximate_pi(Integer.parseInt(s)));
		    
		}
		catch(IOException e)
		{
			e.printStackTrace();
		}
	}
	
}