# Thread: Need help with While Loop

1. Member
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## 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

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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

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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.
Last edited by mrdestroy; 10-17-2008 at 08:27 AM.

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

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If users enter a wrong number (<1), they have to enter again.

6. Use a do-while loop to fix it.

Java Code:
```        int val;

do {
System.out.println("Enter the value: ");
val = keyboard.nextInt();
}while(val < 1);```

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Is there any ideas for while loop, pls???

8. 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:

Java 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.
Last edited by Fubarable; 10-18-2008 at 03:53 PM.

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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?

At least label the end of loops with comments:
} // end while

} // end for(i)

Unformatted code is hard to read.

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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.

12. All depends on your analytical skills.

Java 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);
}```

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That's perfect. Thank you very much.

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