Java exercises PLEASE help...should be easy for most java users!!!!

[ryann18]

1. Write a while loop that verifies that teh user enters a positive integer value.

2. Write a do loop that verifies that teh user enters an even integer value.

3. Write a for loop to print the odd numbers from 1 to 99 (inclusive).

4. Write a for loop to print the multiples of 3 from 300 down to 3.

5. Write a method called alarm that prints the string "Alarm!" multiple times on
seperate lines. The method should accept an integer parameter that
specifies how many times the string is printed. Print an error message if
the parameter is less than 1.

6. Write a method called sumRange that accepts two integers parameters that
represent a range. Issue an error message and return zero if the second
parameter is less than the first. Otherwise, the method should return the
sum of integers in that range (inclusive).

[r035198x]

1. Write a while loop that verifies that teh user enters a positive integer value.

2. Write a do loop that verifies that teh user enters an even integer value.

3. Write a for loop to print the odd numbers from 1 to 99 (inclusive).

4. Write a for loop to print the multiples of 3 from 300 down to 3.

5. Write a method called alarm that prints the string "Alarm!" multiple times on
seperate lines. The method should accept an integer parameter that
specifies how many times the string is printed. Print an error message if
the parameter is less than 1.

6. Write a method called sumRange that accepts two integers parameters that
represent a range. Issue an error message and return zero if the second
parameter is less than the first. Otherwise, the method should return the
sum of integers in that range (inclusive).

You start.

[ryann18]

Im not even sure how to start any of them, this is what I have for #2:

import javax.swing.JOptionPane;
public class KittyKitty {

public static void main (String[] args)
{
String numStr, result;

do
{
System.out.println ("Enter an integer: ");
result = "That number is " + ((num%2 == 0) ? "even" : "odd");
System.out.println (result);

}
while (result > 0);
}
}

[r035198x]

Im not even sure how to start any of them, this is what I have for #2:

import javax.swing.JOptionPane;
public class KittyKitty {

public static void main (String[] args)
{
String numStr, result;

do
{
System.out.println ("Enter an integer: ");
result = "That number is " + ((num%2 == 0) ? "even" : "odd");
System.out.println (result);

}
while (result > 0);
}
}

No that is very bad. Now let's start with number 1, but first a little info and we will be underway.
Are you using jdk1.5 or jdk1.4?
Are familiar with javax.swing.JOptionPane?
Have you done exception handling?

That I believe is all we need to get started on number one.

[ryann18]

I'm using JDK1.5 with netbeans, nah I'm not familiar and I've never used that.

[r035198x]

I'm using JDK1.5 with netbeans, nah I'm not familiar and I've never used that.

Here are the swing components in action. Notice that your program lacked a way of taking in input from the user. Now be honest and say where you do not understand in this code.

import javax.swing.*;
public class Number1 {
    public static void main(String[] args) {
        String input = JOptionPane.showInputDialog(null, "Enter a number");
        int i = input.length() - 1;
        boolean valid = true;
        while(i > 0) {
            if(!Character.isDigit(input.charAt(i))) {
                valid = false;
                break;
            }
            i--;
        }
        if(!valid) {
            JOptionPane.showMessageDialog(null, input+" is not a positive integer");
        }
        else {
            JOptionPane.showMessageDialog(null, input+" is a positive integer");
        }
    }
}

[r035198x]

Of course moving back one decade, we have the non-swing solution

import java.util.Scanner;
public class Number1 {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        System.out.print("Enter your input and press Enter: ");
        String input = scan.nextLine();
        int i = input.length() - 1;
        boolean valid = true;
        while(i > 0) {
            if(!Character.isDigit(input.charAt(i))) {
                valid = false;
                break;
            }
            i--;
        }
        if(!valid) {
            System.out.println(input+" is not a positive integer");
        }
        else {
            System.out.println(input+" is a positive integer");
        }
    }
}
 
 
 

[ryann18]

Of course moving back one decade, we have the non-swing solution

import java.util.Scanner;
public class Number1 {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        System.out.print("Enter your input and press Enter: ");
        String input = scan.nextLine();
        int i = input.length() - 1;
        boolean valid = true;
        while(i > 0) {
            if(!Character.isDigit(input.charAt(i))) {
                valid = false;
                break;
            }
            i--;
        }
        if(!valid) {
            System.out.println(input+" is not a positive integer");
        }
        else {
            System.out.println(input+" is a positive integer");
        }
    }
}
 
 
 

Where does the while loop go in this?

For the second one would I just do basically the same thing except add num%2 for it to become even??

[r035198x]

What do you mean by

Where does the while loop go in this?

?

[ryann18]

What do you mean by ?

Sorry I meant is there any way I can only do a while without an if / else statement?

[r035198x]

Sorry I meant is there any way I can only do a while without an if / else statement?

Not for this one. You have to test that the input satisfies the given conditions and the if/else is tailor made for that.
Now in that Number1, the while condition should read while(i >= 0) for reasons that should now be obvious. I have to knock off to bed now (9:54pm here).

Number 2 does not say the number should be positive. So my solution includes - sign at the start of the number. Here is how you would do it. Now hopefully by tommorrow you will have walked through the rest of the exercises.

import java.util.Scanner;
public class Number1 {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        System.out.print("Enter your input and press Enter: ");
        String input = scan.nextLine();
        int i = input.length() - 1;
        boolean valid = true;
        do {
            if(i == 0) {
                if(!(Character.isDigit(input.charAt(i)) || input.charAt(i) == '-')) {
                    valid = false;
                    break;
                }
            }
            else if(!Character.isDigit(input.charAt(i))) {
                valid = false;
                break;
            }
            i--;
        }
        while(i >= 0);
        if(!valid) {
            System.out.println(input+" is not a Number");
        }
        else {
            int integer = Integer.parseInt(input);
            if(integer % 2 ==0) {
                System.out.println(input+" is a positive even number");
            }
            else {
                System.out.println(input+" is not even");
            }
        }
    }
 
 
}

[ryann18]

Thanks a lot!!!

[r035198x]

Thanks a lot!!!

Hope you finish up the rest on the exercises.