我无法识别我的代码中的错误[关闭]

Question

//我不知道问题出在哪里

包javaapplication3; 导入 java.util.Scanner;

公共类 JavaApplication3 {

public static void main(String[] args) 
{
    Scanner keyboard=new Scanner(System.in);
    int num1,num2;
    String input;
    input= new String();
    char again;
    while (again =='y' || again =='Y')
    {
        System.out.print("enter a number:");
        num1=keyboard.nextInt();
        System.out.print("enter another number:");
        num2=keyboard.nextInt();
        System.out.println("their sum is "+ (num1 + num2));
        System.out.println("do you want to do this again?");
    }

}

Answer 1

您需要将again初始化为某个值，否则会出现编译错误。

另外，在while循环结束时，您需要从扫描器对象中读取数据并将值分配给again变量。检查您修改后的 Java 代码，

Scanner keyboard = new Scanner(System.in);
int num1, num2;
String input;
input = new String();
char again = 'y'; // You need to initialize it to y or Y so it can enter into while loop
while (again == 'y' || again == 'Y') {
    System.out.print("enter a number:");
    num1 = keyboard.nextInt();
    System.out.print("enter another number:");
    num2 = keyboard.nextInt();
    System.out.println("their sum is " + (num1 + num2));
    System.out.println("do you want to do this again?");
    again = keyboard.next().charAt(0); // You need to take the input from user and assign it to again variable which will get checked in while loop condition
}
System.out.println("Program ends");

编辑：这里最好使用do while 循环

检查此代码是否有 do while 循环，您无需担心初始化 again 变量。

Scanner keyboard = new Scanner(System.in);
int num1, num2;
char again;
do { // the loop first executes without checking any condition and you don't need to worry about initializing "again" variable
    System.out.print("enter a number:");
    num1 = keyboard.nextInt();
    System.out.print("enter another number:");
    num2 = keyboard.nextInt();
    System.out.println("their sum is " + (num1 + num2));
    System.out.println("do you want to do this again?");
    again = keyboard.next().charAt(0); // here "again" variable is initialized and assigned the value anyway
} while (again == 'y' || again == 'Y'); // checks the condition and accordingly executes the while loop or quits
keyboard.close();
System.out.println("Program ends");