Question

import java.util.Scanner; 公共课游戏{

public static void main（String [] args）{

Scanner console = new Scanner (System.in);

System.out.println("Playing cards program.");
System.out.println("Give me some numbers and");
System.out.println("I will tell you the appropriate playing card. ");

System.out.println("How many numbers?");
Double a = console.nextDouble();
if (a < 0) { 
  System.out.println("Error should be a positive");
  System.out.println("Re-Enter: ");
    Double b = console.nextDouble();
}
else if (a > 14 || b >14); {
  System.out.println("Error out of range (1-14) ");
  System.out.println("Re-Enter: ");
  Double c = console.nextDouble();

}
if ((a >= 2 && a <= 10)|| (b >= 2 && a <= 10) || (c >= 2 && c <= 10)) {
  if (a ==2 || b == 2 || c == 2) {
    System.out.println("You have a two");
  }
  else if (a ==3 || b == 3 || c == 3) {
    System.out.println("You have a three");
  }
  else if (a ==4|| b == 4 || c == 4) {
    System.out.println ("You have a four");
  }
  else if (a ==5 || b == 5 || c == 5) {
    System.out.println ("You have a five");
  }
  else if (a ==6 || b == 6 || c == 6) {
    System.out.println ("You have a six");
  }
  else if (a ==7 || b == 7 || c == 7) {
    System.out.println ("You have a seven");
  }
  else if (a ==8 || b == 8 || c == 8) {
    System.out.println ("You have a eight");
  }
  else if (a ==9 || b == 9 || c == 9) {
    System.out.println ("You have a nine");
  }
  else if (a ==10 || b == 10 || c == 10) {
    System.out.println ("You have a ten");
  }
}
  if ((a ==1 || a == 11) || (b ==1 || b== 11)||(c ==1 || c == 11)) {
    System.out.println ("You have a Ace");
  }
  if (a== 12 || b == 12 || c == 12) {
    System.out.println ("You have a Jack");
  }
  if (a== 13 || b == 13 || c == 13){
    System.out.println ("You have a Queen");
  }
  if (a== 14 || b == 14 || c == 14) {
    System.out.println ("You have a King");
  }

}

当我编译程序时，我得到一个错误，找不到符号变量b和c。我尝试更改或添加添加但仍显示相同的错误

Answer 1

b和c在if和else if块中定义。因此，它们的范围仅限于那些区块，并且在外部不可见。将b和c的声明移到这些块之外：

Double a = console.nextDouble();
Double b = 0;
Double c = 0;

if (a < 0) { 
    ...
    b = console.nextDouble();
} else if (a > 14 || b > 14); {
    ...
    c = console.nextDouble();
}

Read this有关Java中变量范围的更多信息。

Answer 2

b或c并不总是声明，因为您将声明放在if语句中。如果不满足if，则不声明变量

Java错误变量

2 个答案: