java print a triangle

问题

I'm trying to make a program that takes user input such how long should the triangle be and its direction. The problem I have is that it keeps adding more numbers to the program after I run it.

For example

State the length of the two sides (finish with -1):  5
Should the triangle face down (0) or  up(1): 1
*
**
***
****
*****

2
Should the triangle face down (0) or  up(1): 1
*
**
***
****
*****
******
*******

My code:

import java.util.Scanner; 

public class Triangel {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);

        // Initierings variabler för triangelsida.
        double length = 0;
        double sideLength = 0;

        // This part will ask for user input
        System.out
                .print("State the length of the two sides (finish with -1): ");

        while (sideLength != -1) {
            // Input.
            sideLength = in.nextDouble();
            if (sideLength != -1) {
                // Input will be saved in variable length.
                length += sideLength;

                // This part will ask the user to state whether the triangle is
                // up or down.
                System.out
                        .print("Should the triangle face down (0) or  up(1): ");
                String direction = in.next();

                // if the variables direction is equal to (1) this part will
                // run.
                if (direction.equals("1")) {
                    for (int i = 1; i <= ((int) (length)); i++) {
                        for (int j = 1; j <= i; j++) {
                            System.out.print("*");
                        }
                        System.out.println();
                    }

                }
                // if direction equals to (0) .
                else {
                    for (int i = 1; i <= ((int) (length)); i++) {
                        for (int j = ((int) (length)); j >= 1; j--) {
                            if (j >= i)
                                System.out.print("*");
                        }
                        System.out.println();
                    }
                }

            }

        }

    }

}

回答1:

You have length += sideLength. This will keep adding the sideLength input to the length variable for each cycle of the while loop. What you probably want instead is just length = sideLength.

To make it print out your first prompt again on each iteration, simply put your System.out.print("State the length of the two sides (finish with -1): "); call inside your while loop. (It needs to come before sideLength = in.nextDouble(); as well so that the prompt is displayed before input is entered.)

来源：https://stackoverflow.com/questions/30762509/java-print-a-triangle