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I'm trying to write a code for my computer programming class for a project due Monday, and I'm pretty new to Java, but I'm trying to write a program that will first determine if a number the user inputs is even or odd and then determine if the number is prime or not. I'm not sure if I did the algorithm right or not, so if anyone has any corrections on the program to my algorithm or anything else please say so, but my real issue is that the program is refusing to compile. Every time I try, it says it's having an else without if problem. Here's a link to my command box:

http://s1341.photobucket.com/user/Emi_Nightshade/media/Capture_zps45f9a2ea.png.html

enter image description here Here's my code:

import java.io.*;
import java.util.*;

public class Lesson9p1_ThuotteEmily
{
    public static void main(String args[])
    {
        Scanner kbReader0=new Scanner(System.in);
        System.out.print("

Please enter an integer. An integer is whole number, and it can be either negative or positive. Please enter your number: ");
        long num=kbReader0.nextLong();

        if(num%2==0)                                     //if and else with braces
        {
           System.out.println("Your integer " + num + " is even.");
        }
        else
        {
            System.out.println("Your integer " + num + " is odd.");
        }

        Scanner kbReader1=new Scanner(System.in);
        System.out.print("

Would you like to know if your number is prime? Please enter yes or no: ");
        String yn=kbReader1.nextLine();

        if(yn.equals.IgnoreCase("Yes"))
        {
            System.out.println("Okay. Give me a moment.");

            {
                if(num%2==0)
                {
                    System.out.println("Your number isn't prime.");
                }
                else if(num==2)
                {
                    System.out.println("Your number is 2, which is the only even prime number in existence. Cool, right?");
                }
                for(int i=3;i*i<=n;i+=2)
                {
                    if(n%1==0)
                    {
                        System.out.println("Your number isn't prime.");
                    }
                }
                else
                {
                    System.out.println("Your number is prime!");
                }
            }
        }
        if(yn.equals.IgnoreCase("No"))
        {
            System.out.println("Okay.");
        }
    }
}

If anyone could help me out with this and also any problems I may have made elsewhere in the program, I'd be very grateful! Thanks.

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1 Answer

you have an else statement after a for loop

for(int i=3;i*i<=n;i+=2)
{
    if(n%1==0)
    {
        System.out.println("Your number isn't prime.");
    }
}
else
{
    System.out.println("Your number is prime!");
}

you probably have to make a Boolean variable to do this one. there are various ways to do it, but here's one that I would probably use

boolean isPrime = true;
for(int i=3;i*i<=n;i+=2)
{
    if(n%1==0)
    {
        isPrime = false;
    }
}
if(isPrime)
{
    System.out.println("Your number is prime!");
}
else
{
    System.out.println("Your number isn't prime.");
}

与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
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