Tuesday, 7 June 2016

Displaying prime numbers - Java program

As we know that a number is a prime number if it is a natural number greater than 1 and it can be divided either by 1 or by the number itself. As example - 2, 3, 5, 7, 11, 13, 17 ….

If you take any number and check if it has any divisor you will find that by going that number/2 digits starting from 2 it will have a divisor, if one exists.

As example if number is 8 then you just need to check till 4 to see if it divides by any number or take 15 you just need to check till 7 to see if it divides completely by any number. We'll use the same logic to write our program to check for prime number.

Java program

import java.util.Scanner;

public class PrintPrime {

    public static void main(String[] args) {
        // take input from the user
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter number till which prime numbers are to be printed - ");
        int num = sc.nextInt();
        for(int i = 2; i <= num; i++){
            if(isPrime(i)){
                System.out.print(i + " ");
            }
        }

    }
    
    private static boolean isPrime(int num){
        boolean flag = true;
        // loop from 2, increment it till number/2
        for(int i = 2; i < num/2; i++){
            // no remainder, means divides 
            if(num % i == 0){
                flag = false;
                break;
            }
        }
        return flag;
    }

}

Output

Enter number till which prime numbers are to be printed - 
50
2 3 4 5 7 11 13 17 19 23 29 31 37 41 43 47

Here scanner class is used to get input from the user.

That's all for this topic Displaying prime numbers - Java program. If you have any doubt or any suggestions to make please drop a comment. Thanks!


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