从扫描仪读取字符

Question

对不起Noob问题。这是我第一天尝试Java编程。我需要帮助检索用户想要使用整数的操作符的用户输入。

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); 

    } 
} 

编辑后的版本：

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

运营商：*

第二个数字：3.14

答：31.400000000000002

非常感谢！帮了很多！

Answer 1

好的。这工作，并可以帮助你在你的道路上的java

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 2

在比较中使用==，而不是=（表示分配）。

Answer 3

您需要使用

if (operator == '+') 

通知 '双等于'。

Answer 4

正如其他已经指出的那样，使用==运算符来检查相等性。 =运算符将分配值。

为了读取Scanner中的单个字符，请查看以下问题：Scanner method to get a char。在那里，您会发现使用Scanner.findInLine()方法的建议，该方法接收正则表达式作为参数。提供.通配符作为模式，你将能够得到一个字符串和下一个字符，并使用charAt(0)就可以得到它作为char。

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

当然，你也可以只使用Scanner.next()获得下一个单词为字符串，并且只得到它的第一个字符。但考虑到这样做会从输入缓冲区中丢弃其他字词。