Question

大家好我正在写一个数学测验程序作为一个学习练习，我不能得到这个'响应'变量，以便稍后在方法中识别。具体来说，带有* s的'response'变量不会链接到之前声明的响应变量。我是编程的新手，所以我很确定我会犯一个基本的错误，但我无法解决这个问题，如果有人能帮助我，我将不胜感激。谢谢！

import acm.util.*;
import acm.program.*;


public class MathsQuiz extends ConsoleProgram{

    public void run(){
        println("This program gives atudents a series of maths questions");
        askQuestions();
    }

    private void askQuestions(){
        for (int i = 0; i < NUMBER_OF_QS; i++){
            askQ();
        }
    }

    private void askQ(){
        int answer = rgen.nextInt(0,20);
        int number1 = rgen.nextInt(0,20);
        int number2 = answer - number1;

        if (number2 > 0){
            int response = readInt("What is " + number1 + "+" + number2 + "?");

        }else {
            int response = readInt("What is " + number1 + " " + number2 + "?");
        }

                if (**response** == answer){
                    println("Correct!");
                }else{
                    println("Incorrect");
                }
        }


    private RandomGenerator rgen = RandomGenerator.getInstance(); 

    int NUMBER_OF_QS = 5;
    int RES = 0;
}

Answer 1

将response移至外部范围：

int response;

if (number2 > 0) {
    response = readInt("What is " + number1 + "+" + number2 + "?");
} else {
    response = readInt("What is " + number1 + " " + number2 + "?");
}

局部变量的范围最为有限。这样的变量是只能从声明它的函数或块访问。局部变量的范围来自它们声明的行直到它们的方法或代码块的结束大括号宣布。

Answer 2

您需要在response声明之外定义if：

int response = -1;

if (number2 > 0) {
    response = /* ... Something ... */
} else {
    response = /* ... Something else ... */
}

Answer 3

只需在 if声明之前声明：

int response; if (number2 > 0) { response = ... } else { response = ... }

或者，找出两个块之间的少量差异，并使用条件运算符改变它：

String separator = number2 > 0 ? "+" : " "; int response = readInt("What is " + number1 + separator + number2 + "?");

Answer 4

因为你在if语句中创建了变量响应。试试这个

private void askQ(){
int answer = rgen.nextInt(0,20);
int number1 = rgen.nextInt(0,20);
int number2 = answer - number1;
int response; //to create the variable in the right scope


if (number2 > 0){
    response = readInt("What is " + number1 + "+" + number2 + "?");

}else {
    response = readInt("What is " + number1 + " " + number2 + "?");
}

        if (**response** == answer){
            println("Correct!");
        }else{
            println("Incorrect");
        }
}

Answer 5

response是一个局部变量，其可访问性仅限于声明它的块内部。因此，response只能在if else块中访问。如果您尝试在范围区域之外使用response，则会出现编译时错误，直到您不重新声明它为止。

所以，如果你想使用if else块之外的响应，你必须按如下方式将它声明出来：

int response;
if (number2 > 0){
     response = readInt("What is " + number1 + "+" + number2 + "?");
}else {
     response = readInt("What is " + number1 + " " + number2 + "?");
}

如何在方法中稍后识别此变量？

5 个答案: