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moyack · **on:** January 13, 2013, 11:30:06 AM

Code: Text

package org.moyack;
 
public class Main {
 
        public static void main(String[] args) {
                int a = 10;
                int b = 3;
                System.out.println(max(a, b));
        }
 
        static int max(int a, int b) {
                if (a > b) {
                        return a;
                } else {
                        return b;
                }
        }
 
}
 

cohadar · **Reply #1 on:** January 13, 2013, 11:52:04 AM

Code: Text

package org.moyack;
 
import java.io.IOException;
import java.util.Scanner;
 
/**
 * An example program for reading data from standard input
 * */
public class Main {
 
        public static void main(String[] args) throws IOException {
                // create scanner of system input
                Scanner scanner = new Scanner(System.in);
 
                // define integer and real variables
                int i = 0;
                double d = 0.0;
 
                // print the prompt for user
                System.out.print("i=");
                // read integer variable from console
                // (click down in console window and type in the number)
                i = scanner.nextInt();
 
                // print the prompt for user
                System.out.print("d=");
                // read real variable
                d = scanner.nextDouble();
 
                // print out to see if everything is ok
                System.out.println("i=" + i + ", d=" + d);
 
                // close the scanner to prevent memory leak
                scanner.close();
        }
}
 

cohadar · **Reply #2 on:** January 13, 2013, 12:04:36 PM

Ok here is some homework.

1. Find the sum of odd numbers from a to b (you enter a and b on the console)

2. Enter the radius and height of a cylinder and print out the volume. (http://www.mathopenref.com/cylindervolume.html)
TIP: use java constant Math.PI

moyack · **Reply #3 on:** January 14, 2013, 10:51:14 AM

I've installed eclipse in my linux netbook and I plan to do the homework in my free time @school. One question is:

can I do the homework with vanilla Eclipse??

cohadar · **Reply #4 on:** January 14, 2013, 11:36:28 AM

Yes, we are doing plain java now.

Mobile part is just a plugin for eclipse, we will do that once you get familiar enough with basics of language.

Here are some tutorials
http://www.tutorialspoint.com/java/index.htm

moyack · **Reply #5 on:** January 17, 2013, 10:31:50 PM

The homework thus far:

Code: Text

package moyack.org;
 
import java.io.IOException;
import java.util.Scanner;
 
public class moyack {
 
        /**
         * @param args
         */
        public static void main(String[] args) throws IOException {
                // create scanner of system input
                Scanner scanner = new Scanner(System.in);
 
                // define integer and real variables
                int i = 0;
                int j = 0;
                double t = 0.0;
                double t2 = 0.0;
                while (i >= j) {
                        System.out.println("Please enter the values in order (from minor to mayor)...");
                        System.out.print("first value=");
                        i = scanner.nextInt();
                        System.out.print("second value=");
                        j = scanner.nextInt();
                        if (i > j) {
                        }
                }
                t = i/2;
                t2 = Math.round(i/2);
                System.out.println("t=" + t + " ; t2=" + t2);
 
                // close the scanner to prevent memory leak
                scanner.close();
 
        }
 
}
 

cohadar · **Reply #6 on:** January 19, 2013, 04:57:08 PM

Not like that.
You enter a and b (just 2 numbers) and sum the odd numbers between them (by using some loop)

For example if you enter 4 and 13 your sum is = 5+7+9+11+13
tip: use if inside a loop to separate even and odd numbers

moyack · **Reply #7 on:** January 20, 2013, 10:17:43 PM

Quote from: cohadar on January 19, 2013, 04:57:08 PM

Not like that.
You enter a and b (just 2 numbers) and sum the odd numbers between them (by using some loop)

For example if you enter 4 and 13 your sum is = 5+7+9+11+13
tip: use if inside a loop to separate even and odd numbers

Working on it, sorry for not talking today, I had to do a lot of stuff preparing the classes initiation. Hard working now to ensure free time from the rest of the year... well, sort of...

EDIT: first homework done...

Code: Text

package org.moyack;
 
import java.io.IOException;
import java.util.Scanner;
 
public class Main {
 
        /**
         * @param args
         */
        public static void main(String[] args) throws IOException {
                // create scanner of system input
                Scanner scanner = new Scanner(System.in);
 
                // define integer and real variables
                int i = 0;
                int j = 0;
                int k = 0;
                double t = 0.0;
                double t2 = 0.0;
                while (i >= j) {
                        System.out
                                        .println("Please enter the values in order (from minor to mayor)...");
                        System.out.print("first value=");
                        i = scanner.nextInt();
                        System.out.print("second value=");
                        j = scanner.nextInt();
                }
                t = i / 2.0;
                t2 = Math.round(i / 2.0);
                if (t == t2) {
                        i = i + 1;
                }
                t = j / 2.0;
                t2 = Math.round(j / 2.0);
                if (t == t2) {
                        j = j - 1;
                }
                k = i;
                while (i + 2 <= j) {
                        i = i + 2;
                        k = k + i;
                }
                System.out
                                .println("The sum of all odd numbers from the numbers indicated is: "
                                                + k);
                // close the scanner to prevent memory leak
                scanner.close();
 
        }
}
 

Second EDIT: The other homework done

Code: Text

package org.moyack;
 
import java.io.IOException;
import java.util.Scanner;
 
public class Main {
 
        /**
         * @param args
         */
        public static void main(String[] args) throws IOException {
                // create scanner of system input
                Scanner scanner = new Scanner(System.in);
 
                // define integer and real variables
                double r = 0.0;
                double h = 0.0;
                while (r <= 0 || h <= 0) {
                        System.out
                                        .println("Please enter the values of radius and height of the cylinder...");
                        System.out.println("(These values MUST BE POSITIVE!!!)");
                        System.out.print("radius=");
                        r = scanner.nextDouble();
                        System.out.print("height=");
                        h = scanner.nextDouble();
                }
                System.out.println("the volume of the cylinder is: " + Math.PI * r * r
                                * h);
                scanner.close();
 
        }
}
 

cohadar · **Reply #8 on:** January 21, 2013, 02:50:07 AM

Ok, these programms are "correct" but they are not "good".
Why?

Because they have more stuff than they need to.

Useless local variables

Code: Text

                int k = 0;
                double t = 0.0;
                double t2 = 0.0;
 

Useless code (delete your experiment code)

Code: Text

                t = i / 2.0;
                t2 = Math.round(i / 2.0);
                if (t == t2) {
                        i = i + 1;
                }
                t = j / 2.0;
                t2 = Math.round(j / 2.0);
                if (t == t2) {
                        j = j - 1;
                }
 

Also there is no need to put WHILE around inputs - if user fucks input let the brogram break, not your problem atm.

You need to do both homeworks again.
But this time do it from zero, no copy paste of whole blocks of code.
Make new class for each homework! Homework1, Homework2
And make those classes in org.moyack.homework package
And when you make the homework make sure you write proper comments to explain what code does,
and make sure to delete any bad comments that are left over from copy paste.

Any fool can write code that a computer can understand. Good programmers write code that humans can understand. ~Martin Fowler

moyack · **Reply #9 on:** January 27, 2013, 10:01:47 AM

Ok... I've done the fixes...

Summing odd numbers...

Code: Text

package org.moyack;
 
// Code to sum the odd numbers between 2 integers...
 
import java.io.IOException;
import java.util.Scanner;
 
public class homework1 {
 
        /**
         * @param args
         */
        public static void main(String[] args) throws IOException {
                Scanner scanner = new Scanner(System.in);
                int i = 0;
                int j = 0;
                int k = 0;
                System.out
                                .println("Please enter the values in order (from minor to mayor)...");
                System.out.print("first value="); // first argument
                i = scanner.nextInt();
                System.out.print("second value="); // second argument
                j = scanner.nextInt();
                // finish the code if the data is entered wrong...
                if (i >= j) {
                        System.err
                                        .println("first value is bigger or equal than the second value... exit...");
                        scanner.close();
                        return;
                }
                // checks if i and j are even numbers... if so, they're set to the nearest odd number
                if (i / 2.0 == Math.round(i / 2.0)) {
                        i = i + 1;
                }
                if (j / 2.0 == Math.round(j / 2.0)) {
                        j = j - 1;
                }
                // sums the values between i and j...
                k = i;
                while (i + 2 <= j) {
                        i = i + 2;
                        k = k + i;
                }
                // prints out the result...
                System.out
                                .println("The sum of all odd numbers from the numbers indicated is: "
                                                + k);
                scanner.close();
        }
 
}
 

Calculating cylinder...

Code: Text

package org.moyack;
 
import java.io.IOException;
import java.util.Scanner;
 
public class homework2 {
 
        /**
         * @param args
         */
        public static void main(String[] args) throws IOException {
                // those are the values for the cylinder
                double r = 0.; // radius...
                double h = 0.; // height...
                Scanner scanner = new Scanner(System.in);
                System.out
                                .println("Please enter the values of radius and height of the cylinder...");
                System.out.println("(These values MUST BE POSITIVE!!!)");
                System.out.print("radius=");
                r = scanner.nextDouble();
                System.out.print("height=");
                h = scanner.nextDouble();
                if (r <= 0 || h <= 0) { // checks if r or h are negative values or equal
                                                                // to 0...
                        System.err
                                        .println("radius or height are less or equal to 0... exit...");
                        scanner.close();
                        return;
                }
                // the formulae is calculated directly in the println() function...
                // testing Math.pow... :)
                System.out.println("the volume of the cylinder is: " + Math.PI
                                * Math.pow(r, 2.0) * h);
                scanner.close();
        }
 
}
 

cohadar · **Reply #10 on:** January 28, 2013, 02:55:11 AM

Very good Moyack.

Just one detail.

Code: Text

// this is not an efficient way to check if number is even
if (i / 2.0 == Math.round(i / 2.0)) {
 

Code: Text

// this is how you check if number is even
if (i % 2 == 0) {
 

Code: Text

// this is how you check if number is odd
if (i % 2 != 0) {
 

Code: Text

// always compare with zero, never with 1 because % can return -1 for negative i
if (i % 2 == 1) {   // VERY BAD
 

Ok now try some online tutorials. When you get to the point where you need more help ask here and I will clarify.

http://www.tutorialspoint.com/java/index.htm