Question

我有一个非常好的基本程序;当我输入单个数字时。但是当做一个像1337 - 456 + 32这样的表达时，程序不会继续前进并且表现得像我什么也没做。它没有冻结或输出错误信息，它只是停止了。\

这是代码：

import java.io.*;
import java.util.*;
public class Tester {
    public static void main(String args[]) {
        Scanner kb = new Scanner(System.in);
        System.out.print("Enter number: ");
        String s = kb.nextLine();
        Scanner sc = new Scanner(s);
        //Set delimiters to a plus sign surrounded by any amount of white space...or...
        // a minus sign surrounded by any amount of white space.
        sc.useDelimiter("\\s*");
        int sum = 0;
        int temp = 0;
        int intbefore = 0;

        if (sc.hasNext("\\-")) {
            sc.next();
            if (sc.hasNextInt()) {
                intbefore = sc.nextInt();
                int temper = intbefore * 2;
                intbefore = intbefore - temper; 
            }
        }
        if (sc.hasNextInt()) {
            intbefore = sc.nextInt(); //now its at the sign (intbefore = 5)
        }
        sum = intbefore;

        while (sc.hasNext()) {
            if(sc.hasNext("\\+")) { //does it have a plus sign?
                sc.next(); //if yes, move on (now at the number)
                System.out.println("got to the next();");

                if(sc.hasNextInt()) { //if there's a number
                    temp = sc.nextInt();
                    sum = sum + temp; //add it by the sum (0) and the sum of (5) and (4)
                    System.out.println("added " + sum);
                }
            }
            if(sc.hasNext("\\-")) {
                sc.next();
                System.out.println("got to the next();");

                if (sc.hasNextInt()) {
                    temp = sc.nextInt();
                    sum = sum - temp; //intbefore - temp == 11
                    System.out.println("intbefore: " + intbefore + "  temp: " + temp);
                    System.out.println("subtracted " + sum); // subtracted by 11
                }
            }
        }
        System.out.println("Sum is: " + sum);
    }
}

帮助解决为什么会发生这种情况以及如何解决这个问题？（如果有帮助，我正在使用netbeans）

另外，假设输入在每个数字Ex：123 + -23 - 5

之间有一个空格

Answer 1

我尝试执行你的代码，这就是我找到的。

假设您的输入为12 + 1。

不是c.hasNextInt()会将1分配给intbefore。

接下来，代码中的while循环将进入无限循环cos sc.hasNext()将始终为真（并且在这种情况下返回2）并且它与{2}中的条件不匹配{1}}循环因此使您的代码在无限循环中运行。现在继续努力吧。一切顺利。

Answer 2

首先尝试将分隔符更改为"\\s+"，或者只使用默认分隔符

带有分隔符的2位或更多位数字

2 个答案: