如何解决如果多次选择无效的菜单项，我正在尝试弹出一条消息
目标是如果用户在 3 次中输入无效选项，程序将告诉用户稍后再试并结束程序。我的代码在下面，我希望这是有道理的，如果没有，我很抱歉。如果您有任何问题，请告诉我。我也从来没有在这里问过一个问题，所以它可能没有正确上传。
public static void main(String[] args) {
int num1 = 0,num2 = 0,total = 0,option = 0,ex; // Creates integer variables
do {
Scanner sc = new Scanner(system.in);
System.out.println("\tBasic Math Calculator");// Title
System.out.println("\t---------------------");
System.out.println("\tEnter your choice from the following menu:");
System.out.println("\t------------------------------------------");
System.out.println("1.\tAddition");// All the menu options
System.out.println("2.\tSubtraction");
System.out.println("3.\tMultiplication");
System.out.println("4.\tDivision");
System.out.println("5.\tGenerate Random number");
System.out.println("6.\tQuit");
boolean valid;
do {
valid = true;
try {
option = Integer.parseInt(sc.nextLine());// Stores the users answers
if (option < 1 || option > 6) {
System.out.println("Invalid input. Please try again.");
valid = false;
}
} catch (NumberFormatException e) {
System.out.println("Invalid input. Please try again.");
valid = false;
}
} while (!valid);
switch (option) {// The math and titles for every option
case 1:
System.out.println("You chose to add two numbers: ");
System.out.println("Enter your first number:");
num1 = sc.nextInt();
System.out.println("Enter your second number:");
num2 = sc.nextInt();
total = num1 + num2;
System.out.println("The two numbers you chose added together is " + total);
break;
case 2:
System.out.println("You chose to subtract two numbers: ");
System.out.println("Enter your first number:");
num1 = sc.nextInt();
System.out.println("Enter your second number:");
num2 = sc.nextInt();
total = num1 - num2;
System.out.println("The two numbers you chose subtracted together is " + total);
break;
case 3:
System.out.println("You chose to multiply two numbers: ");
System.out.println("Enter your first number:");
num1 = sc.nextInt();
System.out.println("Enter your second number:");
num2 = sc.nextInt();
total = num1 * num2;
System.out.println("The two numbers you chose multiplied together is " + total);
break;
case 4:
System.out.println("You chose to divide two numbers: ");
System.out.println("Enter your first number:");
num1 = sc.nextInt();
System.out.println("Enter your second number:");
num2 = sc.nextInt();
total = num1 / num2;
if (num2 == 0) {
System.out.println("You can't divide by 0");
} else {
System.out.println("The two numbers you chose divided together is " + total + "with a quotient of "
+ (num1 % num2));
}
break;
case 5:
System.out.println("You chose to get two random numbers: ");
System.out.println("Enter your lower limit:");
num1 = sc.nextInt();
System.out.println("Enter your upper limit:");
num2 = sc.nextInt();
total = num1 + num2;
Random rand = new Random();
int rand_int1 = rand.nextInt(num1 + num2);
System.out.println("The random intigers is: " + rand_int1);
break;
case 6:// If the user wants to quit
ex = 2;
break;
default:// Tells their option was incorrect
System.out.println("Invalid choice,choice " + option + " was not an option");
}
System.out.println("Do you want to continue?1.Yes 2.No");// Asks the user if they want to proceed
ex = sc.nextInt(); // A thank you message for the user for running the program
} while (ex == 1);
System.out.println("-----------------------------------------");
System.out.println("Thank you for using the basic calculator!");
}
解决方法
您可以通过在 start if switch 语句之前创建一个嵌套循环来实现：
//...
System.out.println("6.\tQuit");
boolean valid;
do {
valid = true;
try {
option = Integer.parseInt(sc.nextLine());// Stores the users answers
if (option < 1 || option > 6) {
System.out.println("Invalid input. Please try again.");
valid = false;
}
} catch (NumberFormatException e) {
System.out.println("Invalid input. Please try again.");
valid = false;
}
} while (!valid);
switch (option) {// The math and titles for every option
//...
此更改后的示例运行：
Basic Math Calculator
---------------------
Enter your choice from the following menu:
------------------------------------------
1. Addition
2. Subtraction
3. Multiplication
4. Division
5. Generate Random number
6. Quit
a
Invalid input. Please try again.
9
Invalid input. Please try again.
4
You chose to divide two numbers:
Enter your first number:
在 ideone 查看完整代码。
,您不必使用 echo "<a href='search.php?food=$i'>$prod_ar[$i]</a>"."</br>"; 和 valid 来检查无效输入的次数
如果您想在用户输入 3 个无效选项后退出程序，您必须增加 do-while 的计数并更改 ex 循环中的条件。
初始化while
更改 case 6 和默认如下
ex=1和
while 条件如下
case 6:// If the user wants to quit
System.exit(0);
break;
default:
ex = ex+1;
break;
以下是完整代码
while (ex <4); //
已编辑 下面是示例输出
public static void main(String[] args) {
int num1 = 0,num2 = 0,total = 0,ex= 1; // Creates integer variables
do {
Scanner sc = new Scanner(System.in);
System.out.println("\tBasic Math Calculator");// Title
System.out.println("\t---------------------");
System.out.println("\tEnter your choice from the following menu:");
System.out.println("\t------------------------------------------");
System.out.println("1.\tAddition");// All the menu options
System.out.println("2.\tSubtraction");
System.out.println("3.\tMultiplication");
System.out.println("4.\tDivision");
System.out.println("5.\tGenerate Random number");
System.out.println("6.\tQuit");
switch (option) {// The math and titles for every option
case 1:
System.out.println("You chose to add two numbers: ");
System.out.println("Enter your first number:");
num1 = sc.nextInt();
System.out.println("Enter your second number:");
num2 = sc.nextInt();
total = num1 + num2;
System.out.println("The two numbers you chose added together is " + total);
break;
case 2:
System.out.println("You chose to subtract two numbers: ");
System.out.println("Enter your first number:");
num1 = sc.nextInt();
System.out.println("Enter your second number:");
num2 = sc.nextInt();
total = num1 - num2;
System.out.println("The two numbers you chose subtracted together is " + total);
break;
case 3:
System.out.println("You chose to multiply two numbers: ");
System.out.println("Enter your first number:");
num1 = sc.nextInt();
System.out.println("Enter your second number:");
num2 = sc.nextInt();
total = num1 * num2;
System.out.println("The two numbers you chose multiplied together is " + total);
break;
case 4:
System.out.println("You chose to divide two numbers: ");
System.out.println("Enter your first number:");
num1 = sc.nextInt();
System.out.println("Enter your second number:");
num2 = sc.nextInt();
total = num1 / num2;
if (num2 == 0) {
System.out.println("You can't divide by 0");
} else {
System.out.println("The two numbers you chose divided together is " + total + "with a quotient of "
+ (num1 % num2));
}
break;
case 5:
System.out.println("You chose to get two random numbers: ");
System.out.println("Enter your lower limit:");
num1 = sc.nextInt();
System.out.println("Enter your upper limit:");
num2 = sc.nextInt();
total = num1 + num2;
Random rand = new Random();
int rand_int1 = rand.nextInt(num1 + num2);
System.out.println("The random intigers is: " + rand_int1);
break;
case 6:// If the user wants to quit
System.out.println("Thank you for using the basic calculator!");
System.exit(0);
break;
default:// Tells their option was incorrect
ex=ex+1;
System.out.println("Invalid choice,choice " + option + " was not an option");
}
System.out.println("Do you want to continue?1.Yes 2.No");// Asks the user if they want to proceed
//ex = sc.nextInt(); // A thank you message for the user for running the program
} while (ex<4);
System.out.println("-----------------------------------------");
System.out.println("Thank you for using the basic calculator!");
}
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