在 while 循环中停止重复的 Println，BlueJ

Question

下面是我目前的代码，它是我的计算机科学的计算器 class。我遇到的问题是在程序的第二个运行上 System.out.print("Would you like to perform a calculation? (y/n) "); 运行s 两次而不是一次。我已经上交了这个项目，但我想知道它为什么会这样，以及在我未来的项目中如何修复它。我将 post 下面的其余代码。

感谢大家的帮助，"A"感谢大家的帮助。谢谢！

/**
* A calculator with multiple functions.
* @author () 
* @version (version 2.1)
*/
import java.io.*;
import java.util.Scanner;
public class Calc
{
  public static void main(String args[])
  {
    Scanner reader = new Scanner(System.in);
    String cont = "", funct = "";
    double fnum = 0, snum = 0, answer = 0;

    while(true)
    {
        System.out.print("Would you like to perform a calculation? (y/n) ");
        cont = reader.nextLine();
        if (cont.equalsIgnoreCase("y"))
        {
            System.out.println("What function would you like to do?");
            System.out.println("+?");
            System.out.println("-?");
            System.out.println("*?");
            System.out.println("/?");
            funct = reader.nextLine();
            if (funct.equals("+"))
            {
                System.out.println("Simple addition calculator");
                System.out.println("Enter first num: ");
                fnum = reader.nextDouble();
                System.out.println("Enter second num: ");
                snum = reader.nextDouble();
                answer = fnum + snum;
                System.out.println("Answer: " + answer);
                System.out.println(" ");
            }
            if (funct.equals("-"))
            {
                 System.out.println("Simple subtraction calculator");
                System.out.println("Enter first num: ");
                fnum = reader.nextDouble();
                System.out.println("Enter second num: ");
                snum = reader.nextDouble();
                answer = fnum - snum;
                System.out.println("Answer: " + answer);
                System.out.println(" ");
            }
            if (funct.equals("*"))
            {
                 System.out.println("Simple multiplication calculator");
                System.out.println("Enter first num: ");
                fnum = reader.nextDouble();
                System.out.println("Enter second num: ");
                snum = reader.nextDouble();
                answer = fnum * snum;
                System.out.println("Answer: " + answer);
                System.out.println(" ");
            }
            if (funct.equals("/"))
            {
                 System.out.println("Simple division calculator");
                System.out.println("Enter first num: ");
                fnum = reader.nextDouble();
                System.out.println("Enter second num: ");
                snum = reader.nextDouble();
                answer = fnum / snum;
                System.out.println("Answer: " + answer);
                System.out.println(" ");
            }
        }
        else if (cont.equalsIgnoreCase("n"))
        {
            break;
        }

    }
  }
}

Answer 1

尝试添加这个 reader.nextLine();在 while 循环结束之前，如下所述。这将清除屏幕缓冲区。

else if (cont.equalsIgnoreCase("n")) { break; } reader.nextLine(); } 希望这有帮助，

Answer 2

基本上，当您使用 reader.nextLine() 方法时，缓冲区中仍然有一个换行符，调用 nextLine() 时会拾取该换行符。所以它用换行符制作了一个额外的运行。如果你运行你的程序使用换行符作为输入，即使是第一次，它也会循环而不做任何事情。因此，您只需要在进入 while 循环之前清除缓冲区。

Answer 3

在循环内的所有函数条件中，您使用的是 reader.nextDouble()。这只会读取数字（例如“8”）输入，而不是用户在数字后输入的新行（回车）。 minus(-) 函数的以下代码不会打印 "Would you like to perform a calculation? (y/n) " 两次，因为新行已被读取。这里使用reader.nextLine()代替reader.nextDouble()。 reader.nextLine() 将读取整行，而不仅仅是数字。

if (funct.equals("-"))
        {
            System.out.println("Simple subtraction calculator");
            System.out.println("Enter first num: ");
            fnum = Double.parseDouble( reader.nextLine());
            System.out.println("Enter second num: ");
            snum = Double.parseDouble( reader.nextLine());
            answer = fnum - snum;
            System.out.println("Answer: " + answer);
            System.out.println(" ");
        }

Answer 4

您需要在调用nextDouble() 之后和下一个nextLine() 之前消耗换行符，以防止nextLine() 消耗换行符。否则 funct = reader.nextLine(); 将把换行符作为输入并且不等待任何更多的用户输入，这会导致重复。

if (funct.equals("/"))
            {
                System.out.println("Simple division calculator");
                System.out.println("Enter first num: ");
                fnum = reader.nextDouble();
                System.out.println("Enter second num: ");
                snum = reader.nextDouble(); // consume the new line character
                reader.nextLine();
                answer = fnum / snum;
                System.out.println("Answer: " + answer);
                System.out.println(" ");
            }

在 while 循环中停止重复的 Println，BlueJ

Stopping a repeating Println in a while loop, BlueJ

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