Question

• Write a program to find the prime numbers IN JAVA

Ask user to input the integer number test the number whether it is a prime number or not Then, print “true” or “false” depending on whether the number is prime or isn’t. Hint: number is prime when is has exactly 2 factors: one and itself. By this definition, number 1 is a special case and is NOT a prime. Use idea of user input, cumulative sum, and loop to solve this problem. You can assume user inputs positive number.

Answer 1

The following is the code for the above question.

import java.util.Scanner;
public class Main
{
        public static void main(String[] args) {
            Scanner in=new Scanner(System.in);
                int i,num;
                boolean isPrime=true; //a boolean type to check if the num is prime or not
                System.out.print("Enter any number to check whether it is prime or not: ");
                num=in.nextInt(); //input number
                System.out.println();
                if(num==1) //if num is 1, then it is not prime (you can also add condition if num<0 to get rid of negative numbers)
                {
                    isPrime=false; //set isPrime to false =>not prime
                }
                else
                {
                for(i=2;i<num;i++) //loop check from 2 to num. You can also use i<=n/2 for reducing time complexity
                {
                    if(num%i==0) //if it has any factor
                    {
                        isPrime=false; //set isPrime to false and break the loop
                        break;
                    }
                }
                
                }
                if(isPrime) //check if isPrime
                {
                    System.out.println("true"); //print true
                }
                else
                {
                    System.out.println("false"); //else print false
                }
        }
}

I am also attaching the output and code screenshot for your reference.

Output and code screenshot:

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