Can someone help me write this simple while loop?

1

I am currently trying to figure out how to code this simple while loop based on the instructions.

The instructions:
Given some positive number n, write a while loop that will print the odd numbers from -n to n (inclusive), one number per line. The given number may be even or odd.

My code so far:

int n = 3;
	while (n >= -36)
       {
	      System.out.println(n);
          n--;
       }
2

What problems are you having?

If n is 3, then -n would be -3, not -36.

3

Alrighty, the loop is a reasonable start.

Three comments:

  1. “print the odd numbers” Where is your logic for checking if a number is odd before you print?

  2. "from -n to n", you seem to be going from n to -n (decreasing instead of increasing)

  3. Why not use n in the loop bounds? Or a copy of it?

4

I don’t know how to create the logic for checking if a number is odd.

5

How do you check if a number is even or odd on paper?

6

I guess I would do (n % 2 == 1).

7

Right. On paper you would see if the number has a remainder when divided by 2. The code you gave n % 2 == 1 checks that same thing.

8

So would I write

int n = 3;
	while (n % 2 == 1 && n >= -36)
       {
	     System.out.println(n);
         n++;
       }
9

I suspect that if you try to run this code, it will not do what you want.

Here is how I would describe the instructions

  • Loop from -n to n, inclusive

  • Print all odd numbers

Do you have experience with if statements?

10

Would I do something like

if (n % 2 == 1)
{
    System.out.println(n);
}
11

Sure, that would check if a value is odd. But where did the looping go?

12

I don’t know where to put the looping. Would I put it inside the if statement or outside?

13

Well,

if (condition1) {
  while (condition2) {
  }
}

will run a loop if a condition is true.

while (condition2) {
  if (condition1) {
  }
}

will execute the body of a loop based upon some criteria.

Which is closer to “print only odd numbers in a range”?

14

Could I do:

int n = 3;
if (n % 2 == 1) 
{
  while (n >= -36)
   {
	      System.out.println(n);
          n++;
   }
}
15

What happens when you run the code? Do you get the output you want?

16

No, it’s giving me unending numbers. How do I f ix it?

17

Is this condition ever met?

18

I think it does. It’s giving me a lot of numbers.

19

I meant to say, is this condition ever not met? Do you do anything to stop your code from meeting this condition so the loop will stop?

20

No, I don’t. Would I need a loop control variable?