如何在 Java 的循环中重置变量？

How can I reset a variable in a loop in Java?

提问by Seth Myers

I am writing a number-guessing game for my Computer Science 1100 class, one part of which is to print the number of attempts the player takes at guessing the target number. I've defined a variable triesto track that; the program increments it by one every time the player makes a guess.

我正在为我的计算机科学 1100 课程编写一个猜数字游戏，其中一部分是打印玩家猜目标数字的尝试次数。我已经定义了一个变量tries来跟踪它；每次玩家猜测时，程序都会将其加一。

The game restarts after the player guesses the number correctly, and at that point I want to reset the triescounter. I can't figure out how to do that, however, because the program increments trieseach time the number is guessed. How can I do it?

在玩家正确猜出数字后游戏重新开始，此时我想重置tries计数器。然而，我无法弄清楚如何做到这一点，因为tries每次猜到数字时程序都会增加。我该怎么做？

import java.util.Scanner;
import java.util.Random;
public class Q2 {
   public static void main(String[] args) {
      Scanner kbd = new Scanner(System.in);
      Random r = new Random();
      System.out.println("Welcome to the Number Guessing Game");
      int x=0;//defining x for later
      int tries = 1;//defining tries for later
      while (x!=-1) { 
         int y = r.nextInt(101);//defining random number 0-100
         System.out.print("Guess a number between 0 and 100 or enter -1 to quit: ");
         x=kbd.nextInt();//redefining x
         x=kbd.nextInt();//redefining x
         for (int i=1;x!=-1&&x!=y;i=1) {//for loop
               if (x<-1||x>100) {//illegal condition
                  System.out.print("Out of bounds. Try again: ");
               }
               else if (x>y) {//input greater than random condition
                  System.out.print("The number is lower. Try again: ");
               }
               else if (y>x) {//random greater than input condition
                  System.out.print("The number is higher. Try again: ");
               }
               x = kbd.nextInt();//redefining x
               tries+=i;//defining pattern for tries
         }
         if (x==y) {//input=random condition
            System.out.println("Congratulations! You guessed the number in " + tries + " tries");
         }
      }
      if (x==-1) {//quit condition
         System.out.print("Thank you for playing the game!!");
         }
     }
}

回答by Frithjof

a) Change the scope of your variable

a) 改变变量的作用域

Variables are only available in the scope they are defined in. For example

变量仅在定义它们的范围内可用。例如

while (something) { // all code inside the loop is in an inner scope
  int variable = 42;
  // variable is accessible here
}
// variable is not accessible here

This means, every time the while-loop performs one iteration, variable is newly created. It is a good practice to only define variables in the scope they actually have a meaning (in this case in the while-loop).

这意味着，每次 while 循环执行一次迭代时，都会新创建变量。一个好的做法是只在它们实际具有意义的范围内定义变量（在这种情况下是在 while 循环中）。

b) Assign the variable every time anew

b) 每次重新分配变量

Another way would be to reset the variable each time it is necessary. This would result in such a design:

另一种方法是在每次需要时重置变量。这将导致这样的设计：

int variable; // variable is defined outside the inner scope
while (something) {
  variable = 42;
  // some code that changes variable's value
}

回答by kdek

One possible solution would be to encapsulate your guessing game into it's own method, which will re-initialize all variables when called, and create an ifcondition inside of your loop if the guess is correct.

一种可能的解决方案是将您的猜谜游戏封装到它自己的方法中，该方法将在调用时重新初始化所有变量，并if在猜测正确时在循环内部创建一个条件。

private static void guessingGame() {
    Scanner scanner = new Scanner(System.in);
    double randomNum = Math.random();
    double tries = 0, guess = 0;

    do while (!(guess == randomNum) {
        System.in("What is your guess? ");
        guess = scanner.nextDouble();
        tries++;

        if (guess == randomNum) {
           System.out.println("Guessed correctly in " + tries + " tries.");
           tries = 0;
        }
    }
}

public static void main() {
   guessingGame();
}