//OutputFormat.java

/**
 * Solution to Self-Test Question 30.
 */
public class OutputFormat
{
    /**
     * Displays a number with digitsAfterPoint digits after
     * the decimal point. Rounds any extra digits.
     * Does not advance to the next line after output.
     */
    public static void write
    (
        double number,
        int digitsAfterPoint
    )
    {
        if (number >= 0)
            writePositive(number, digitsAfterPoint);
        else
        {
            double positiveNumber = -number;
            System.out.print('-');
            writePositive(positiveNumber, digitsAfterPoint);
        }
    }

    /**
     * Displays a number with digitsAfterPoint digits after
     * the decimal point. Rounds any extra digits.
     * Advances to the next line after output.
     */
    public static void writeln
    (
        double number,
        int digitsAfterPoint
    )
    {
        write(number, digitsAfterPoint);
        System.out.println();
    }

    //Precondition: number >= 0
    //Displays a number with digitsAfterPoint digits after 
    //the decimal point. Rounds any extra digits.
    private static void writePositive
    (
        double number,
        int digitsAfterPoint
    )
    {
        int mover = (int)(Math.pow(10, digitsAfterPoint));
        //1 followed by digitsAfterPoint zeros
        int allWhole; //number with the decimal point
        //moved digitsAfterPoint places
        allWhole = (int)(Math.round(number * mover));
        int beforePoint = allWhole / mover;
        int afterPoint = allWhole % mover;
        System.out.print(beforePoint);
        System.out.print('.');
        writeFraction(afterPoint, digitsAfterPoint);
    }

    //Displays the integer afterPoint with enough zeros
    //in front to make it digitsAfterPoint digits long.
    private static void writeFraction
    (
        int afterPoint,
        int digitsAfterPoint
    )
    {
        int n = 1;
        while (n < digitsAfterPoint)
        {
            if (afterPoint < Math.pow(10, n))
                System.out.print('0');
            n = n + 1;
        }
        System.out.print(afterPoint);
    }

    public static void main(String[] args)
    {
        double number = 123.456789;
        System.out.println("Testing with the number 123.456789:");
        writeln(number, 0);
        writeln(number, 1);
        writeln(number, 2);
        writeln(number, 3);
        writeln(number, 4);
        writeln(number, 5);
        writeln(number, 6);
        writeln(number, 7);
    }
}