运行时扫描变量的错误

Question

我是 Java 编程的初学者。我想解决形式的表达 (a+2⁰b)+(a+2⁰b+2¹b)+........+ (a+2⁰b+...+2^(n-1)b) 以 a、b 和 n 的形式为您提供“q”查询每个查询，打印对应于给定 a、b 和 n 值的表达式值。这意味着
样本输入：
2
0 2 10
5 3 5
样本输出：
4072
196

我的代码是：

import java.util.Scanner;

public class Expression {

public static void main(String[] args) {
    // TODO Auto-generated method stub
    Scanner in = new Scanner(System.in);
    int q=in.nextInt();
    for(int i=0;i<q;i++){
        int a = in.nextInt();
        int b = in.nextInt();
        int n = in.nextInt();
    }
    int expr=a+b;                 //ERROR:a cannot be resolved to a variable
    for(int i = 0; i<n;i++)       //ERROR:n cannot be resolved to a variable
        expr+=a+Math.pow(2, i)*b; //ERROR:a and b cannot be resolved to variables
    System.out.print(expr);
    in.close();
}

}

Answer 1

这里的错误是在for循环中声明a、b和n，这意味着当循环结束时变量也会丢失，垃圾收集器会处理它们。

解决这个问题真的很简单

public static void main(String[] args) {
    // TODO Auto-generated method stub
    Scanner in = new Scanner(System.in);
    int q=in.nextInt();
    int a, b, n;               // Declare outside if you need them outside ;)
    for(int i=0;i<q;i++){
        a = in.nextInt();
        b = in.nextInt();
        n = in.nextInt();
    }
    int expr=a+b;              //ERROR:a cannot be resolved to a variable
    for(int i = 0; i<n;i++) {  //ERROR:n cannot be resolved to a variable
        expr+=a+(2*i)*b;       //ERROR:a and b cannot be resolved to variables
        System.out.print(expr);
    }
    in.close();
}