我已经发布了关于我的例子的问题，这是不同的问题。我遇到了另一个问题。当我选择选项3（乘）时，我得到的结果为零。如果我选择选项4，则不能除以零（零是我的哨兵）。当我使用int输入要计算的数字时，如何使sentinel成为字符串或char？这是代码。
import java.util.Scanner;
public class SwitchLoopNumbers {
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
int numbers = 0;
int result = 0;
int option;
boolean quit = true;
String done = "";
do {
System.out.println("CALCULATOR MENU");
System.out.println("********** ****");
System.out.println("\n1. Add");
System.out.println("2. Substract");
System.out.println("3. Multiply");
System.out.println("4. Divide");
System.out.println();
System.out.print("Enter your option >> ");
option = scan.nextInt();
while (quit) {
switch (option) {
case 1:
System.out.print("Enter a number, type 0 when done >> ");
numbers = scan.nextInt();
if (numbers == 0) {
quit = false;
}
result += numbers;
break;
case 2:
System.out.print("Enter a number, type 0 when done >> ");
numbers = scan.nextInt();
if (numbers == 0) {
quit = false;
}
result = numbers - result;
break;
case 3:
System.out.print("Enter a number, type 0 when done >> ");
numbers = scan.nextInt();
if (numbers == 0) {
quit = false;
}
result *= numbers;
break;
case 4:
System.out.print("Enter a number, type 0 when done >> ");
numbers = scan.nextInt();
if (numbers == 0) {
quit = false;
}
result = result / numbers;
break;
}
}
System.out.println("The total is: " + result);
System.out.println("Back to main menu ? y/n ");
scan.nextLine();
done = scan.nextLine();
numbers = 0;
result = 0;
quit = true;
} while ("y".equalsIgnoreCase(done));
System.out.println("Thank you for using calculator");
}
}
答案 0 :(得分：0)
你的主要问题是你已经将result初始化为零，这对于加法和减法来说是一个很好的方法，但是当它涉及乘法时它不会起作用。因此，作为该问题的解决方案，您必须将变量设置为Integer，因此您可以根据需要在循环内更改它，具体取决于您尝试执行的操作。此外，它更好，因为类Integer允许您将其变量分配给null，这在这种情况下非常方便（例如，比使用0更好）。您遇到的另一个问题是您声明当前操作结束并返回结果的方式。您使用0作为停止循环的方法，但0可用作计算中的数字。因此，您应该将输入扫描为字符串，然后如果用户输入=符号，则循环结束并返回结果。然后，您还可以使用Integer类提供给我们的功能，它允许我们从字符串中解析整数并将它们用作常规数字。除此之外，你还有一些语法＆＃34;错误＆＃34;并声明你可以更好地编写它。
总的来说，如果你想制作一个真正的计算器，这绝对不是最好的方法，因为你可能面临许多数学问题和例外，但它并不是一个很好的开始。 这可以解决您的大多数问题：
import java.util.Scanner;
public class SwitchLoopNumbers {
public static void main(String[] args) {
String number;
String process = "";
Integer result = null;
int option = 0;
boolean startOver = true;
while (true) {
Scanner scan = new Scanner(System.in);
if (startOver) {
System.out.print("CALCULATOR MENU" + "\n"
+ "****************" + "\n"
+ "1. Add" + "\n"
+ "2. Substract" + "\n"
+ "3. Multiply" + "\n"
+ "4. Divide" + "\n"
+ "****************" + "\n"
+ "Enter your option >> ");
option = scan.nextInt();
}
switch (option) {
case 1:
System.out.print("Enter a number, or '=' to get the result >> ");
number = scan.next();
if ("=".equals(number)) {
process = process.replaceFirst("[ + \t]+$", " = ");
break;
} else if (result == null) {
result = Integer.parseInt(number);
process += number + " + ";
option = 1;
startOver = false;
continue;
} else {
result = result + Integer.parseInt(number);
process += number + " + ";
option = 1;
startOver = false;
continue;
}
case 2:
System.out.print("Enter a number, or '=' to get the result >> ");
number = scan.next();
if ("=".equals(number)) {
process = process.replaceFirst("[- \t]+$", " = ");
break;
} else if (result == null) {
result = Integer.parseInt(number);
process += number + " - ";
option = 2;
startOver = false;
continue;
} else {
result = result - Integer.parseInt(number);
process += number + " - ";
option = 2;
startOver = false;
continue;
}
case 3:
System.out.print("Enter a number, or '=' to get the result >> ");
number = scan.next();
if ("=".equals(number)) {
process = process.replaceFirst("[ * \t]+$", " = ");
break;
} else if (result == null) {
result = Integer.parseInt(number);
process += number + " * ";
option = 3;
startOver = false;
continue;
} else {
result = result * Integer.parseInt(number);
process += number + " * ";
option = 3;
startOver = false;
continue;
}
case 4:
System.out.print("Enter a number, or '=' to get the result >> ");
number = scan.next();
if ("=".equals(number)) {
process = process.replaceFirst("[ / \t]+$", " = ");
break;
} else if (result == null) {
result = Integer.parseInt(number);
process += number + " / ";
option = 4;
startOver = false;
continue;
} else {
result = result / Integer.parseInt(number);
process += number + " / ";
option = 4;
startOver = false;
continue;
}
}
System.out.println("The result of " + process.replace("+ 0 ", "") + result);
System.out.print("Back to main menu? [y/n]: ");
if (scan.next().equalsIgnoreCase("y")) {
process = "";
result = null;
startOver = true;
} else if (scan.next().equalsIgnoreCase("n")) {
System.out.println("Thank you for using calculator.");
break;
} else {
System.out.println("Wrong input!");
break;
}
}
}
}