java - 需要帮助理解有关 While 循环条件语句和类型转换的一些基本 Java 概念

Question

我只是想编写一个简单的计算器，它工作正常......

我现在想做的是包含一个“do while”或“while”循环来重复语句，直到用户输入四个基本运算符号之一。我已经使用其他方法(if 和 switch)实现了它，但我想简化它。

此外，我在学习如何在 scanner 和 JPane 方法中解析字符时遇到了很多问题。我可以使用互联网上的各种资源来实现，但是一个简单的方法可以帮助我更清楚地理解逻辑而不仅仅是实现，我将非常感激......

    public class MyCalculator{
    public static void main (String [] args){

    // Let us code a simple calculator
    char OP;
    System.out.println("This is a simple calculator that will do basic calculations such as :\nAddition, Multiplication, Substraction and Division.");

    // Create a scanner object to Read user Input.
    Scanner input = new Scanner(System.in);

    System.out.println("Enter Any positive number followed by pressing ENTER.");
    int firstNum = input.nextInt();

    // Need to Loop the below statement till one of the four (+,-,*,/) operator is entered.

    System.out.println("Enter your choice of OPERATOR sign followed by pressing ENTER.");
    OP = input.next().charAt(0);

    System.out.println("Enter your Second number followed by an ENTER stroke.");
    int secNum = input.nextInt();

    // Various possible Resolution
    int RSum = firstNum+secNum;
    int RSubs= firstNum-secNum;
    int RPro = firstNum*secNum;
    double DPro = firstNum/secNum;

    // Conditional statements for Processing
    Switch (OP){ 
    case '+': System.out.println("The Resulting sum is "+ RSum);
    break;
    case '-': System.out.println("The Resulting sum is "+ RSubs);
    break;
    case '*': System.out.println("The Resulting Product is "+ RPro);
    break;
    case '/': System.out.println("The Resulting Divisional product is "+ DPro);
    break;
    default : System.out.println("Try Again");

        }

    }
}

Answer 1

你可以使用这样的东西:

while(scanner.hasNext()) {
  //some code
   int number = scanner.NextInt();
}

但我会实现一个计算器，如下所示:

int num1 = scanner.NextInt();
String op = scanner.Next();
int num2 = scanner.NextInt();

您可以按如下方式循环遍历字符串并进行检查:

for (char ch : exampleString.toCharArray()){
  System.out.println(ch);
}

您还可以按如下方式循环遍历字符串:

for (int i=0; i<examplestring.length(); i++) {
  char c = examplestring.charAt(i);
}

您可以循环直到得到 + 或 - ，如下所示:

char operator;    
do {
  char operator = scanner.next().get(0);
}while(operator != '+' || operator != '-')

您可以循环并打印错误消息，如下所示:

char operator;
do {
  char operator = scanner.next().get(0);
  if(!isValidOperator(operator)) {
    System.out.println("invalid operator");
  }
}while(!isValidOperator(operator))

public boolean isValidOperator(char operator) {
  if(operator == '+') {
    return true;
  } else if (operator == '-') {
    return true;
  }

  return false;
}