How to Find Prime Number in Java?

Question

Hello
I have java project that user need to enter int = number and find prime number.

Problem: When I Enter 10 Does't Print Any Thing.

public class Prime_Numbers {
    
    public static void main(String[] args)
    {
        // Scanner
        Scanner scan = new Scanner(System.in);
        
        // Variables
        int num = 10, i = 2;
        
        // Ask User For Input
        System.out.println("Please Enter Number: ");
        num = scan.nextInt();
        
        while(i <= num/2)
        {
            if(num % i == 2) 
            {
                System.out.println(num);
                break;  
            }
        }
    }
}

Infinite loop. Neither `i` nor `num` ever changes within the loop. — Fred Larson, Mar 10 '21 at 18:55
`while` loop is infinite because neither `i` nor `num` are changed; with `num = 10` nothing can be printed because `10 % 2 == 0` and condition in `if` is always false. The following question: [...trying to write a code to check if a number is prime...](https://stackoverflow.com/questions/65968558/return-a-boolean-value-using-if-else-in-java/65969133#65969133) has answers how to find a prime number. — Nowhere Man, Mar 10 '21 at 18:56

score 1 · Answer 1 · edited Mar 10 '21 at 18:59

1

If you look at the if statement inside your while-loop, nothing inside gets executed. The reason is the condition of the if-statement: (num % i == 2). Since 10%2 is not equal to 2, nothing will be printed. Rather, it is equal to 0. If you are trying to check if num is an even number, then change num % i == 2 to num % i == 0.

edited Mar 10 '21 at 18:59

luk2302

55,258
23
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answered Mar 10 '21 at 18:55

RW77

64
1
8

I try this num % i == 0 but not showing correct output it just showing input number – Neel Patel Mar 10 '21 at 19:07

Satyajit Bhatt · Answer 2 · 2021-03-10T19:22:50.363

0

You can try this code :

import java.util.Scanner;
public class PrimeNumberExample {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter number : ");
        int number = scanner.nextInt();
        boolean flag = false;
        
        for(int count=2; count<number; count++) {
            if(number%count == 0) {
                flag = true;
                break;
            }
        }
        
        if(!flag) {
            System.out.println(number + " is Prime");
        } else {
            System.out.println(number + " is Not Prime");   
        }   
    }
}

edited Mar 10 '21 at 19:22

answered Mar 10 '21 at 19:01

Satyajit Bhatt

211
1
7

i try to run the program you provide but out put is not showing.--- exec-maven-plugin:3.0.0:exec (default-cli) @ Prime_Numbers --- Enter number : 10 ------------------------------------------------------------------------ BUILD SUCCESS ------------------------------------------------------------------------ Total time: 3.998 s Finished at: 2021-03-10T14:04:02-05:00 – Neel Patel Mar 10 '21 at 19:04
Which IDE you are using ? – Satyajit Bhatt Mar 10 '21 at 19:05
Apache Netbeans 12.2 – Neel Patel Mar 10 '21 at 19:06
Program run but output not display in console am i right ? – Satyajit Bhatt Mar 10 '21 at 19:08
Just try above program in notepad and run it on console hope so you get exact output – Satyajit Bhatt Mar 10 '21 at 19:11
Just one question to you which number you entered always ? – Satyajit Bhatt Mar 10 '21 at 19:19
Again run above code and i understand your problem now it will work fine – Satyajit Bhatt Mar 10 '21 at 19:23

score 0 · Answer 3 · answered May 08 '22 at 14:36

maybe you can try find prime number code

public class PrimeExample{
     public static void main(String args[]){
          int i,m=0,flag=0;
          int n=5;//it is the number to be checked
          m=n/2;
          if(n==0||n==1){
                System.out.println(n+" is not prime number");
          }else{
           for(i=2;i<=m;i++){
                if(n%i==0){
                    System.out.println(n+" is not prime number");
                    flag=1;
                    break;
                }
           }
           if(flag==0)  {
                System.out.println(n+" is prime number");
            }
      }
}

How to Find Prime Number in Java?

3 Answers3