What's missing in this java number printing exercise?

[maniku]

Hi there,

Working on the following exercise: write code which asks the user for upper limit num, then prints the numbers in the following sequence:

if num limit is e.g. 8, the printout has to be: 1 8 2 7 3 6 4 5.

My code:

import java.util.*;

public class T59_Vuorotellen {

    private static Scanner input = new Scanner(System.in);

    public static void main(String[] args) {
        System.out.print("Give number: ");
        int num = Integer.parseInt(input.nextLine());

        for (int i = 1; i < num; i++) {
            int a = num--;
            int b = i;
            System.out.print(b + " ");
            System.out.print(a + " ");
        }
    }
}

It works, nearly:

-If num limit is even, it behaves as supposed to.
-If num limit is odd, it leaves the last number to be printed out. E.g. if limit is 9, it prints 1 9 2 8 3 7 4 6 when it SHOULD print 1 9 2 8 3 7 4 6 5

If I replace < with <= or add +1 to num in the for loop, the result is still as should be with even nums, and with odd numbers the last number IS printed but twice. Scratching my head here.

[Solarsonic]

int increasingNum=1; // initialization
int decreasingNum=9; // initialization

while(increasingNum<9 && decreasingNum>1) {
System.out.print(increasingNum + " ");
System.out.print(decreasingNum + " ");
increasingNum++;
decreasingNum--;
}

[maniku]

int increasingNum=1; // initialization
int decreasingNum=9; // initialization

while(increasingNum<9 && decreasingNum>1) {
System.out.print(increasingNum + " ");
System.out.print(decreasingNum + " ");
increasingNum++;
decreasingNum--;
}

Thanks but that's not it. It prints: 1 9 2 8 3 7 4 6 5 5 6 4 7 3 8 2

The code is supposed to stop when it has printed all the numbers between 1 and the user input limit. I appreciate the suggestion, however was hoping to find whatever is the bit that is missing from the code that I have?

[Solarsonic]

Thanks but that's not it. It prints: 1 9 2 8 3 7 4 6 5 5 6 4 7 3 8 2

The code is supposed to stop when it has printed all the numbers between 1 and the user input limit. I appreciate the suggestion, however was hoping to find whatever is the bit that is missing from the code that I have?

Just realized I misread your problem -.-

[maniku]

Just realized I misread your problem -.-

No worries, thanks for trying to help though.

[Norm]

Try debugging your code by adding some printlns
For example:

System.out.println("<i=" + i + ", num=" + num + ">");

[Junky]

for (int i = 1; i < num; i++) {
            int a = num--;

The loop iterates while i is less than num. Your problem is that inside the loop you change the value of num thus your loop never executes the required number of iterations. Since i is increasing by 1 and num is decreasing by 1 the condition is met twice as fast as expected.

[Norm]

The println I suggested will show that very clearly.