一個(gè)基本的計(jì)算器能夠加、減、乘或除兩個(gè)數(shù)字。這是使用開關(guān)盒完成的。演示這一點(diǎn)的程序如下 

例子

import java.util.Scanner;
public class Calculator {
   public static void main(String[] args) {
      double num1;
      double num2;
      double ans;
      char op;
      Scanner reader = new Scanner(System.in);
      System.out.print("Enter two numbers: ");
      num1 = reader.nextDouble();
      num2 = reader.nextDouble();
      System.out.print("\nEnter an operator (+, -, *, /): ");
      op = reader.next().charAt(0);
      switch(op) {
         case '+': ans = num1 + num2;
            break;
         case '-': ans = num1 - num2;
            break;
         case '*': ans = num1 * num2;
            break;
         case '/': ans = num1 / num2;
            break;
      default: System.out.printf("Error! Enter correct operator");
         return;
      }
      System.out.print("\nThe result is given as follows:\n");
      System.out.printf(num1 + " " + op + " " + num2 + " = " + ans);
   }
}

輸出

Enter two numbers: 10.0 7.0
Enter an operator (+, -, *, /): -
The result is given as follows:
10.0 - 7.0 = 3.0

現(xiàn)在讓我們了解一下上面的程序。

這兩個(gè)號(hào)碼以及運(yùn)營商都是從用戶那里獲取的。演示這一點(diǎn)的代碼片段如下

double num1;
double num2;
double ans;
char op;
Scanner reader = new Scanner(System.in);
System.out.print("Enter two numbers: ");
num1 = reader.nextDouble();
num2 = reader.nextDouble();
System.out.print("\nEnter an operator (+, -, *, /): ");
op = reader.next().charAt(0);

switch case 用于對(duì)兩個(gè)數(shù)字執(zhí)行指定的操作。如果輸入的操作員不正確，則會(huì)顯示錯(cuò)誤消息。演示這一點(diǎn)的代碼片段如下

switch(op) {
   case '+': ans = num1 + num2;
      break;
   case '-': ans = num1 - num2;
      break;
   case '*': ans = num1 * num2;
      break;
   case '/': ans = num1 / num2;
      break;
default: System.out.printf("Error! Enter correct operator");
return;
}

最后，打印結(jié)果。演示這一點(diǎn)的代碼片段如下 

System.out.print("\nThe result is given as follows:\n");
System.out.printf(num1 + " " + op + " " + num2 + " = " + ans);