java - 从扫描仪读取一个字符

Question

对不起菜鸟问题。这是我尝试 Java 编程的第一天。我需要帮助检索用户想要与整数一起使用的运算符的用户输入。

import java.util.Scanner;

public class calculator {

    public static void main (String args[]) {

        Scanner number = new Scanner(System.in);
        double num1,num2,answer;
        char operator;

        System.out.println("Enter first number: ");
        num1 = number.nextDouble();

        operator = number.nextChar(); /* the "nextChar" is not correct */

        System.out.println("Enter second number: ");
        num2 = number.nextDouble();

        if (operator = '+'){
            answer = num1 + num2; /* If statements do not work like this */
        }                             /* I would use "else if", unsure if it allows */
        if (operator = '-'){
            answer = num1 - num2;
        }
        if (operator = '*'){
            answer = num1 - num2;
        }
        if (operator = '/'){
                answer = num1 / num2;
        }

        System.out.println(num1 + num2 + operator + answer);

    }
}

编辑版本：

import java.util.Scanner;

public class calculator{

    public static void main (String args[]) {

        Scanner userInput = new Scanner(System.in);

        String operator;
        double num1,num2,answer = 0;



        System.out.println("Enter first number: ");
        num1 = userInput.nextDouble();

        System.out.println("Enter operator: ");
        operator = userInput.next();


        System.out.println("Enter second number: ");
        num2 = userInput.nextDouble();

        if (operator.equals ("+")){
            answer = num1 + num2;
        }
        else if (operator.equals ("-")){
            answer = num1 - num2;
        }
        else if (operator.equals ("*")){
            answer = num1 * num2;
        }
        else if (operator.equals ("/")){
                answer = num1 / num2;
        }

        System.out.println("First number:" + num1);
        System.out.println("Operator:" + operator);
        System.out.println("Second number:" + num2);

        System.out.println("Answer: " + answer);
    }
}

第一个数字：10.0

操作员：*

第二个数字：3.14

答案：31.400000000000002

非常感谢你们！帮助很大！

Answer 1

在比较中使用 ==，而不是 =（这意味着分配）。

Answer 2

正如其他人已经指出的那样，使用==运算符来检查是否相等。操作员将=改为分配值。

为了从 中读取单个字符Scanner，请查看以下问题：Scanner method to get a char。在那里你会找到使用Scanner.findInLine()方法的建议，它接收一个正则表达式作为参数。提供.通配符作为模式，您将能够获得一个带有下一个字符的字符串，并charAt(0)在其上使用，您将获得一个char.

Scanner sc = new Scanner("abc");
char ch = sc.findInLine(".").charAt(0);
System.out.println(ch); // prints "a"

当然，您也可以只使用Scanner.next()将下一个单词作为字符串获取，然后仅获取其第一个字符。但要考虑到这样做会从输入缓冲区中丢弃单词的其余部分。

Answer 3

好的。这很有效，可以帮助您在通往 Java 的道路上

public class Tester4 {

    public static void main(String args[]) {

        Scanner input = new Scanner(System.in);
        double num1, num2, answer = 0;
        String operator;

        System.out.println("Enter first number: ");
        num1 = input.nextDouble();

        System.out.println("Enter operator: ");
        operator = input.next();

        System.out.println("Enter second number: ");
        num2 = input.nextDouble();

        if(operator.equals("+")) {
            answer = num1 + num2;
        } else if(operator.equals("-")) {
            answer = num1 - num2;
        } else if(operator.equals("*")) {
            answer = num1 - num2;
        } else if(operator.equals("/")) {
            answer = num1 / num2;
        }

        System.out.println("First number:" + num1);
        System.out.println("Operator:" + operator);
        System.out.println("Second number:" + num2);

        System.out.println("Answer: " + answer);
    }

}

Answer 4

你需要使用

if (operator == '+') 

注意'双等于'。