primes

Write a Program to print the Prime numbers ?

This java program prints prime numbers, number of prime numbers required is asked from the user. Remember that smallest prime number is 2.

Source code of the Program:

import java.util.*;

class PrimeNumbers
{
public static void main(String args[])
{
      int n, status = 1, num = 3;

      Scanner in = new Scanner(System.in);
      System.out.println("Enter the number of prime numbers you want");
      n = in.nextInt();

      if (n >= 1)
      {
      System.out.println("First "+n+" prime numbers are :-");
      System.out.println(2);
      }

      for ( int count = 2 ; count <=n ;  )
      {
      for ( int j = 2 ; j <= Math.sqrt(num) ; j++ )
      {
      if ( num%j == 0 )
      {
      status = 0;
      break;
      }
      }
      if ( status != 0 )
      {
      System.out.println(num);
      count++;
      }
      status = 1;
      num++;
      }        
}
}

Output of the Program:

We have used sqrt method of Math package which find square root of a number. To check if an integer(say n) is prime you can check if it is divisible by any integer from 2 to (n-1) or check from 2 to sqrt(n), first one is less efficient and will take more time.