编写一个用于计算器的程序以将表达式接受为字符串，其中操作数和运算符之间用零个或多个空格分隔

Question

编写用于计算器的程序，以将表达式接受为字符串，其中操作数和运算符之间用零个或多个空格分隔。例如：3 + 4和3 + 4是可接受的表达式。

Answer 1

import java.util.Scanner;
 class pro13
{
    public static void main(String[] args) {
        Scanner s1=new Scanner(System.in);
        System.out.println("Enter Calculation:");
        String a=s1.nextLine();

        a = a.replaceAll(" ","");

        a = a.replaceAll("[+]","#+#");
        a = a.replaceAll("[-]","#-#");
        a = a.replaceAll("[*]","#*#");
        a = a.replaceAll("[/]","#/#");
        args = a.split("#");

        // Check number of strings passed
        if (args.length != 3) {
            System.out.println(
                "Usage: java Calculator operand1 operator operand2");
            System.exit(0);
        }

        // The result of the operation
        int result = 0;

        // Determine the operator
        switch (args[1].charAt(0)) {
            case '+' : result = Integer.parseInt(args[0]) +
                                      Integer.parseInt(args[2]);
                          break;
            case '-' : result = Integer.parseInt(args[0]) -
                                      Integer.parseInt(args[2]);
                          break;
            case '*' : result = Integer.parseInt(args[0]) *
                                      Integer.parseInt(args[2]);
                          break;
            case '/' : result = Integer.parseInt(args[0]) /
                                      Integer.parseInt(args[2]);
                          break;
        }

        // Display result
        System.out.println(args[0] + ' ' + args[1] + ' ' + args[2]
            + " = " + result);
    }
}