Can't figure out what I am doing wrong in this method ( compute_even )

Question

I am having some problem understanding how I am supposed to do the compute_even method in this exercise, I hope someone can help me out.

Nevermind the compute_odd method I am still thinking about that one!

Here is the exercise:

Write a void method called choose_function that has a parameter n of type int. If the value of n is even the method will call the method compute_even passing to it value of the parameter n, else the method will call the method compute_odd passing to it the value of n.

The two methods will print on the console the following sequence:

compute_even: 2, 4, 8, 16, 32, 64, 128… up to n

compute_odd: 1, 3, 6, 10, 15, 21, 28 … up to n

Write program in which the user enter an int numbers n1 greater than zero (hence the program will prompt the user to enter a value until the condition is not satisfied). The program will print on the console the sequence associated to the value of n1.

public static void main(String[] args)
{
    Scanner input = new Scanner(System.in);
    int n1;
    do
    {
        System.out.println("Enter a positive integer value: ");
        n1 = input.nextInt();
    }while(n1 <= 0);

    choose_function(n1);

    input.close();
}

public static void choose_function(int n)
{
    if(n%2 == 0)
        System.out.print(compute_even(n));
    else
        System.out.print(compute_odd(n));
}

public static int compute_even(int k)
{
    int r = 1;
    do
    {
        r = r*2;
        return r;
    }while(r <= k);
}

public static int compute_odd(int k)
{

}

strong text

Answer 1

The problem is here.

int r = 1;
do
{
    r = r*2;
    return r;
} while(r <= k);

This code will return 2 every time to the caller. Why? Because in your loop, you set r = 1 * 2 = 2, then return r immediately. What you want to do instead is check if this new r is equal tot he passed parameter. If not, then print r and a space, and continue looping. If it IS equal, then print the final number and return from the method.

int r = 1;
do
{
    r = r*2;
    System.out.print(r + " ");
    if (r == k) return r;
}while(r <= k);

Answer 2

Try this Code

public static void main(String[] args) {
    Scanner input = new Scanner(System.in);
    int n1;
    do {
        System.out.println("Enter a positive integer value: ");
        n1 = input.nextInt();
    } while (n1 <= 0);

    choose_function(n1);
    System.out.println();
    input.close();
}

public static void choose_function(int n) {
    if (n % 2 == 0) {
        compute_even(n);
    } else {
        compute_odd(n);
    }
}

public static void compute_even(int k) {
    int r = 0;
    while (r <= k) {
    System.out.print(""+r+" ");
        r = r + 2;  
    } 
}
public static void compute_odd(int k) {
    int r = 1;
    while (r <= k){
        System.out.print(""+r+" ");
        r = r+2;   
    }
}

Try printing values inside compute_odd and compute_even method seperately. It seems there is a problem with your algorithm as well,

You should use

int r =0;
r = r+2 // returns 0 2 4 6 8...

instead of using

int r = 1;
r = r*2;  // This would return 2 4 8 16...

Sample output :

Enter a positive integer value:

-5

Enter a positive integer value:

5

1 3 5