java - 如何使用 if/else 树中的变量值作为随后 while 循环的变量值

Question

这是我到目前为止编写的程序代码。它说我还没有初始化答案。我想在 if/else 树执行后使用 answer 的值将数字转换为星号。

import java.io.*;
import java.util.*;

public class Project5 {
    public static void main(String[] args){
        System.out.println("Please enter a formula of this form:operator,operand,operand(ex. add,2,2):");
        // wanted to change things but was not sure how far I was allowed to go so I used commas instead of spaces
        //was trying to split with a delimiter but kept getting an error [Ljava.lang.String;@55e83f9
        Scanner input = new Scanner(System.in);
        String formula = input.nextLine();
        System.out.println(formula);
        String oper = formula.substring(0,3);
        System.out.println(oper);
        String fnum = formula.substring(4,5);
        System.out.println(fnum);
        String snum = formula.substring(6,7);
        System.out.println(snum);
        double freal = Integer.parseInt(fnum);
        System.out.println(freal);
        double sreal = Integer.parseInt(snum);
        double answer;
        if (oper.equalsIgnoreCase("add") == true){
            answer = freal+sreal;
            System.out.println(answer);
        }
        else if(oper.equalsIgnoreCase("subtract") == true){
                 answer = freal-sreal;
            System.out.println(answer);
        }
        else if(oper.equalsIgnoreCase("multiply") == true){
                 answer = freal*sreal;
            System.out.println(answer);
        }
        else if(oper.equalsIgnoreCase("divide") == true){
                 answer = freal/sreal;
            System.out.println(answer);
        }
        else
            System.out.println("not valid.");

        while(answer > 0){
            System.out.print("*");
            answer--;
    }
}}

Answer 1

因为在最后的 else 分支中，您没有为 answer 分配值。如果这是执行的树，那么当您进入 while 循环时，它将是未定义的。您可以通过最初将 answer 初始化为某个值或确保 if/else 树的每个分支都为 answer 分配一个值来解决此问题。

编辑要解决您的问题，请更改

double answer;

至

double answer = 0.0;

这将解决问题。