Thread: determining a prime number

Required:

Write a java program that asks a user to input a positive integer value. The program must keep on asking for an input if the user enters a non-positive integer value. Once a valid input is accepted, your program must output an appropriate message whether the value is a prime number or not.
Finally, the user will be asked if he/she would like to try again. It must be noted that the user will be repeatedly asked for an input until a valid response (pressing ‘Y’ or ‘y’ for YES; and ‘N’ or ‘n’ for NO) is entered.
Solve this problem using modular approach.

import java.util.Scanner;
 
public class PrimeNumber {
	public static void main(String[] args) {
 
	Scanner kbd = new Scanner(System.in);
	int num;
	boolean again;
 
 
	do {
		num = inputPositiveInt();
		if (isPrime(num)) {
			System.out.println("Input is a prime number.");
		} else {
			System.out.println("Input is a non-prime number.");
		}
 
//		again = tryAgain();
	} while (again); {
	System.out.println("Thank you for testing this program.");
	}
 
}
 
 
	public static int inputPositiveInt() {
		int num;
		Scanner kbd = new Scanner(System.in);
		System.out.print("Please enter a positive integer.");
		num = kbd.nextInt();
		if (num < 0) {
			System.out.println("Inputted integer value is non-positive");
		}
	}
 
	public static boolean tryAgain() {
		Scanner kbd = new Scanner(System.in);
		System.out.print("Would you like to try again?");
		char again;
		again = kbd.charAt(0);
		if (again.equals('y') || again.equals('Y')) {
			return true;
		}
 
		else if (again.equals('n') || again.equals('N')) {
			System.exit(0);
		}
	}
 
	public static boolean isPrime(int num) {
			boolean isPrime = true;
 
		for(int i = 2; i<num; i++) {
        if(num % i == 0) {
        isPrime = false; 
        break;
        } 
 
 
        }
        return true;
	}
 
}

ERRORS:

F:\PrimeNumber.java:41: error: cannot find symbol
        again = kbd.charAt(0);
                   ^
  symbol:   method charAt(int)
  location: variable kbd of type Scanner
F:\PrimeNumber.java:42: error: char cannot be dereferenced
        if (again.equals('y') || again.equals('Y')) {
                 ^
F:\PrimeNumber.java:42: error: char cannot be dereferenced
        if (again.equals('y') || again.equals('Y')) {
                                      ^
F:\PrimeNumber.java:46: error: char cannot be dereferenced
        else if (again.equals('n') || again.equals('N')) {
                      ^
F:\PrimeNumber.java:46: error: char cannot be dereferenced
        else if (again.equals('n') || again.equals('N')) {
                                           ^

i am simply frustrated because of getting errors like everywhere. been doin this for like 2hours or so.
i would appreciate it if someone could fix this for me. if possible.. ASAP. because i need it soon. thanks

done editting.

update

import java.util.Scanner;
 
public class PrimeNumber {
	public static void main(String[] args) {
 
	Scanner kbd = new Scanner(System.in);
	int num;
	boolean again;
 
 
	do {
		num = inputPositiveInt();
		if (isPrime(num)) {
			System.out.println("Input is a prime number.");
		} else {
			System.out.println("Input is a non-prime number.");
		}
 
//		again = tryAgain();
	} while (again); {
	System.out.println("Thank you for testing this program.");
	}
 
}
 
 
	public static int inputPositiveInt() {
		int num;
		Scanner kbd = new Scanner(System.in);
		System.out.print("Please enter a positive integer.");
		num = kbd.nextInt();
		if (num < 0) {
			System.out.println("Inputted integer value is non-positive");
		}
	}
 
	public static boolean tryAgain() {
		Scanner kbd = new Scanner(System.in);
		System.out.print("Would you like to try again?");
		char again;
		again = kbd.nextInt();
		if (again == 'y') || (again == 'Y') {
			return true;
		}
 
		else if (again == 'n') || (again == 'N') {
			System.exit(0);
		}
	}
 
	public static boolean isPrime(int num) {
			boolean isPrime = true;
 
		for(int i = 2; i<num; i++) {
        if(num % i == 0) {
        isPrime = false; 
        break;
        } 
 
 
        }
        return true;
	}
 
}

errors:

F:\PrimeNumber.java:42: error: illegal start of expression
        if (again == 'y') || (again == 'Y') {
                          ^
F:\PrimeNumber.java:42: error: ';' expected
        if (again == 'y') || (again == 'Y') {
                                           ^
F:\PrimeNumber.java:46: error: 'else' without 'if'
        else if (again == 'n') || (again == 'N') {
        ^
F:\PrimeNumber.java:46: error: illegal start of expression
        else if (again == 'n') || (again == 'N') {
                               ^
F:\PrimeNumber.java:46: error: ';' expected
        else if (again == 'n') || (again == 'N') {

Originally Posted by Norm

The if statement's condition need to be enclosed in ()s. The () must surround ALL of the sub conditions.

fixed. lol.

import java.util.Scanner;
 
public class PrimeNumber {
	public static void main(String[] args) {
 
	Scanner kbd = new Scanner(System.in);
	int num;
	boolean again;
 
 
	do {
		num = inputPositiveInt();
		if (isPrime(num)) {
			System.out.println("Input is a prime number.");
		} else {
			System.out.println("Input is a non-prime number.");
		}
 
//		again = tryAgain();
	} while (again); {
	System.out.println("Thank you for testing this program.");
	}
 
}
 
 
	public static int inputPositiveInt() {
		int num;
		Scanner kbd = new Scanner(System.in);
		System.out.print("Please enter a positive integer.");
		num = kbd.nextInt();
		if (num < 0) {
			System.out.println("Inputted integer value is non-positive");
		}
	}
 
	public static boolean tryAgain() {
		Scanner kbd = new Scanner(System.in);
		System.out.print("Would you like to try again?");
		char again;
		again = kbd.nextLine();
		if (again == 'y' || again == 'Y') {
			return true;
		}
 
		else if (again == 'n' || again == 'N') {
			System.exit(0);
		}
	}
 
	public static boolean isPrime(int num) {
			boolean isPrime = true;
 
		for(int i = 2; i<num; i++) {
        if(num % i == 0) {
        isPrime = false; 
        break;
        } 
 
 
        }
        return true;
	}
 
}

and another error..

F:\PrimeNumber.java:41: error: incompatible types
        again = kbd.nextLine();
                            ^
  required: char
  found:    String
1 error