Question

我是java和编程的新手有人可以建议可以使用什么，以便答案必须等于+,-,*,/ ?目前我正在尝试创建一个if语句，但我收到一个错误，我不太清楚为什么。有人可以查看我的代码并帮我完成if语句吗？如果您对可以改进的内容有任何其他建议，请分享。

import java.util.Scanner;

public class Calculator {
public static void main (String Args []) {
    Scanner input = new Scanner(System.in);
    double firstNumber, secondNumber;
    String equationOperator;

    System.out.println("Please give your first number: \t");
    firstNumber = input.nextDouble();
    System.out.println("Please give your second number: \t");
    secondNumber = input.nextDouble();
    System.out.println("Which equation would you like to perform?");
    System.out.println("Please enter one of the following + - / * \t");
    equationOperator = input.next();

    switch (equationOperator) {
    case "+":
        System.out.println("Your chosen equation is: Adding");
        System.out.println("Your answer is: " + (firstNumber + secondNumber));
        break;
    case "-":
        System.out.println("Your chosen equation is: Subtracting");
        System.out.println("Your answer is: " + (firstNumber - secondNumber));
        break;
    case "/":
        System.out.println("Your chosen equation is: Dividing");
        System.out.println("Your answer is: " + (firstNumber / secondNumber));
        break;
    case "*":
        System.out.println("You chosen equation is: Multiplying");
        System.out.println("Your answer is: " + (firstNumber * secondNumber));
        break;                  
    }
    if (!equationOperator.equals("+ || - || / || *") {
        System.out.println("Please choose one of the following:");
        System.out.println("+"
                + "-"
                + "/"
                + "*");
                }
    System.out.println("\t Thank You for using my Calculator");

        }


 }

Answer 1

您在条件中错过了一个右括号：

if (!equationOperator.equals("+ || - || / || *") {

应该是

if (!equationOperator.equals("+ || - || / || *")) {

请注意，这不会给您预期的结果，因为您正在检查完全字符串＆＃34; + || - || / || *＆＃34;。

您需要多个equals，例如

if (!equationOperator.equals("+") && !equationOperator.equals("-") ...) {

或仅在default声明中使用switch案例：

switch (equationOperator) {
    case "+":
        System.out.println("Your chosen equation is: Adding");
        System.out.println("Your answer is: " + (firstNumber + secondNumber));
        break;
    case "-":
        System.out.println("Your chosen equation is: Subtracting");
        System.out.println("Your answer is: " + (firstNumber - secondNumber));
        break;
    case "/":
        System.out.println("Your chosen equation is: Dividing");
        System.out.println("Your answer is: " + (firstNumber / secondNumber));
        break;
    case "*":
        System.out.println("You chosen equation is: Multiplying");
        System.out.println("Your answer is: " + (firstNumber * secondNumber));
        break;
    default:
        System.out.println("Please choose one of the following:");
        System.out.println("+"
            + "-"
            + "/"
            + "*");         
}

当其他任何一个匹配时，将执行default个案。有关详细信息，请参阅the documentation。

Answer 2

在开关

中使用默认大小写

default:
                System.out.println("Please choose one of the following:");
        System.out.println("+"
                + "-"
                + "/"
                + "*");
                }

此外，你的if语句不正确，除了支架从最后丢失。

if（！equationOperator.equals（“+ || - || / || *”））这将您的equationOperator与字符串“+ || - || / || *”进行比较。

你想要这个

if（！（equationOperator.equals（“+”）|| equationOperator.equals（“ - ”）|| equationOperator.equals（“/”）|| equationOperator.equals（“*”）））{

简单计算器 - 如果声明

2 个答案: