Need help with While Loop

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• 10-17-2008, 07:19 AM
mrdestroy
Need help with While Loop
I got a problem with this one, hope you guys can help me. I've just learned Java few weeks.

Write a program segment that reads a natural number n (n>=1) from keyboard, then
calculates and displays the sum of all odd numbers from 1 to n. Use the while loop to
validate input, if the number is smaller than 1, display an error message and the user
can try again.

Sample run:
Please enter a natural number greater than 1: -1
Invalid value. Please enter a natural number greater than 1: 9
Sum of odd from 1 to 9 is: 25

Thanks in advanced.
• 10-17-2008, 07:46 AM
Unome
Whats your problem? You don't know how to make a while loop?
while (decisioin)
{
//data and calculations
}

to calculate the sum of the odd numbers test a /2 and see if you get a whole number or a number with decimals. if it has a remainder than its an odd number!

hope that helps. clarify what part of the problem your having difficulty with
• 10-17-2008, 08:21 AM
mrdestroy
import java.util.Scanner;

public class OddNumberSum {

/**
* @param args
*/
public static void main(String[] args) {
int n = 1;

Scanner keyboard = new Scanner(System.in);

while (n >= 1){
System.out.println("Please enter a natural number greater than 1: ");
n = keyboard.nextInt();

}
{
System.out.println("Invalid value, Please enter a natural number greater than 1: ");
n = keyboard.nextInt();
//This is for enter again.
}

}
}

How can I calculate the sum of odd numbers.
Example:
If I enter 9, it means I have to calculate the sum of 1, 3, 5, 7, 9.
If I enter 8, I have to calculate the sum of 1, 3, 5, 7.
• 10-17-2008, 08:39 AM
Supamagier
dude wtf?
Code:

```} { System.out.println("Invalid value, Please enter a natural number greater than 1: "); n = keyboard.nextInt(); //This is for enter again. }```
• 10-17-2008, 11:43 AM
mrdestroy
If users enter a wrong number (<1), they have to enter again.
• 10-18-2008, 10:54 AM
Eranga
Use a do-while loop to fix it.

Code:

```        int val;                 do {             System.out.println("Enter the value: ");             val = keyboard.nextInt();         }while(val < 1);```
• 10-18-2008, 01:14 PM
mrdestroy
Is there any ideas for while loop, pls???
• 10-18-2008, 03:18 PM
Fubarable
what do you mean "any ideas for while loop?" You've been given some great ideas above. Let's see the latest of what you have in code, and then a decent question about that code.

Also, when posting your code, please use code tags so that your code will retain its formatting and be readable. To do this, you will need to paste already formatted code into the forum, highlight this code, and then press the "code" button at the top of the forum Message editor prior to posting the message. Another way is to place the tag &#91;code] at the top of your block of code and the tag &#91;/code] at the bottom, like so:

Code:

```&#91;code]   // your code block goes here.   // note the differences between the tag at the top vs the bottom.   // note that this code has to already be properly formatted with 3-4 space indentations for code tags to work &#91;/code]```

good luck.
• 10-18-2008, 04:53 PM
mrdestroy
public static void main(String[] args) {
int n = 1, sum = 0;

Scanner keyboard = new Scanner(System.in);

while (n >= 1){
System.out.println("Please enter a natural number greater than 1: ");
n = keyboard.nextInt();
for(int i = 1; i <= n; i += 2)
{
sum += i;
}
System.out.println("Sum of odd numbers from 1 to " + n + " is: " + sum);
}
{
System.out.println("Invalid value, Please enter a natural number greater than 1: ");
n = keyboard.nextInt();
}

}
}
This is my code in while loop, but when I run this printed out "Please enter a natural number greater than 1:" again.
How can I stop this repeat?
• 10-18-2008, 05:00 PM
Norm
Please see above about posting code with code tags.
At least label the end of loops with comments:
} // end while

} // end for(i)

Unformatted code is hard to read.
• 10-18-2008, 10:10 PM
Eranga
I've no idea that why are are stick with the while loop. Do while is solution you have.
• 10-19-2008, 05:16 AM
mrdestroy
Thank you all very much. But, while is a requirement in this problem, I have to do it following while. Do while from Mod is really great. I'm just new here so I didnt know about code tag. I will fix it in others.
• 10-20-2008, 10:38 AM
Eranga
All depends on your analytical skills.

Code:

```    public static void main(String[] args) {         int n = 1, sum = 0;         Scanner keyboard = new Scanner(System.in);         System.out.println("Please enter a natural number greater than 1: ");         n = keyboard.nextInt();                 while (n <= 1){             System.out.println("Invalid number, Please enter a natural " +                     "number greater than 1: ");             n = keyboard.nextInt();         }         for(int i = 1; i <= n; i += 2) {             sum += i;         }         System.out.println("Sum of odd numbers from 1 to " + n + " is: " + sum);     }```
• 10-20-2008, 02:28 PM
mrdestroy
That's perfect. Thank you very much.
• 10-20-2008, 02:29 PM
Eranga
You are welcome. Is that what you are looking?