Question

在处理完这段代码一段时间后，我已经遇到了意想不到的问题。选项'B'和'C'的if和else语句在输入用户输入时不会在屏幕上显示任何内容。我尝试过一些东西，但我似乎无法弄明白。

import java.util.Scanner;
public class Internet_Service_Provider
{
    public static void main(String[] args)
    {
        double hours;
        char choice;

        Scanner input = new Scanner(System.in);

        System.out.println ("Enter the letter of your package: ");
        choice = input.nextLine().charAt(0);

        System.out.println ("Enter the number of hours used: ");
        hours = input.nextDouble();

        double chargesa, chargesb, chargesc;
        chargesa = 9.95;
        chargesb = 13.95;
        chargesc = 19.95;

        double chargesa2, chargesb2;
        chargesa2 = (hours - 10) * 2;
        chargesb2 = (hours - 20);

        double extrafeesA, extrafeesB;
        extrafeesA = chargesa + chargesa2;
        extrafeesB = chargesb + chargesb2;

        if (choice == 'A')
            if (hours <= 10) { 
                System.out.println ("Your total charges are: " + chargesa);
            }
        else if (choice == 'A')
            if (hours > 10){
                 System.out.println ("your total charges are: " + extrafeesA);
             }
        else if (choice == 'B')
            if (hours <= 20) {
                 System.out.println ("Your total charges are: " + chargesb);
            }
        else if (choice == 'B')
            if (hours > 20){
                 System.out.println ("Your total charges are: " + extrafeesB);
            }
        else if (choice == 'C'){
             System.out.println ("Your total charges are: " + chargesc);
        }
    }
}

当用户键入“A”然后键入小时数时，程序运行完美并为我提供所需的输出。如果输入“B”或“C”然后输入小时数，则屏幕上没有输出。造成这种情况的原因是什么？

CNC中在检查响应之前我弄乱了代码并发现如果删除else并创建此代码：

  if (choice == 'A')
        if (hours <= 10) { 
              System.out.println ("Your total charges are: " + chargesa);
        }

  if (choice == 'A')
        if (hours > 10){
              System.out.println ("your total charges are: " + extrafeesA);
        }

  if (choice == 'B')
        if (hours <= 20) {
              System.out.println ("Your total charges are: " + chargesb);
        }

  if (choice == 'B')
        if (hours > 20){
              System.out.println ("Your total charges are: " + extrafeesB);
        }

  if (choice == 'C'){
        System.out.println ("Your total charges are: " + chargesc);}

......程序运行正常。我想其他的陈述是不必要的并且引起了问题。

Answer 1

if (choice == 'A'){
    if (hours <= 10) { 
      System.out.println ("Your total charges are: " + chargesa);}
    else if (choice == 'A')
      if (hours > 10){
      System.out.println ("your total charges are: " + extrafeesA);}
    else if (choice == 'B')
      if (hours <= 20) {
      System.out.println ("Your total charges are: " + chargesb);}
    else if (choice == 'B')
      if (hours > 20){
      System.out.println ("Your total charges are: " + extrafeesB);}
    else if (choice == 'C'){
      System.out.println ("Your total charges are: " + chargesc);}
    }
}

只是添加一些适当的表格显示，除了“A”之外，你实际上并没有涵盖任何其他情况。制表使代码看起来更清晰，因此更容易找到错误。您需要正确使用大括号，因为现在您只检查选择=='A'。如果没有 - 你的代码什么都不做。

Answer 2

你有if(choice == 'A')给你带来麻烦。还要检查另一个不正确缩进的大括号。这很难读。代码应该人类可读

请参阅：

if (choice == 'A')// this is giving trouble to you
if (hours <= 10) { 
  .
  .

此代码相当于，（增加了大括号）

if (choice == 'A'){
    if (hours <= 10) {
     .
     . 
}

所以你必须删除它。你想要做的更清楚的是这个。您可以使用switch

switch(choice){
 case 'A':
       System.out.println ("Your total charges are: " + (hours <=10) ?chargesa:extrafeesA);
       break;
 case 'B':
       System.out.println ("Your total charges are: " + (hours <=10) ?chargesB:extrafeesB);
       break;
 case 'C':
       System.out.println ("Your total charges are: " + chargesc);
       break; 
 }

Answer 3

尝试正确使用大括号：）

if (choice == 'A') {
   if (hours <= 10) 
      System.out.println ("Your total charges are: " + chargesa);
   if (hours > 10)
       System.out.println ("your total charges are: " + extrafeesA);
}
else if (choice == 'B') {
   if (hours <= 20)
      System.out.println ("Your total charges are: " + chargesb);
   if (hours > 20)
      System.out.println ("Your total charges are: " + extrafeesB);
}
else if (choice == 'C')
   System.out.println ("Your total charges are: " + chargesc);

Answer 4

您可以简单地使用“AND”以使您的条件正常工作。

if (choice == 'A' && hours <= 10) { 
  System.out.println ("Your total charges are: " + chargesa);
}
else if (choice == 'A' && hours > 10) {
  System.out.println ("your total charges are: " + extrafeesA);
}
else if (choice == 'B' && hours <= 20)  {
  System.out.println ("Your total charges are: " + chargesb);
}
else if (choice == 'B' && hours > 20) {
  System.out.println ("Your total charges are: " + extrafeesB);
}
else if (choice == 'C'){
  System.out.println ("Your total charges are: " + chargesc);
}

Answer 5

改变这个：

if (choice == 'A')
if (hours <= 10) { 
  System.out.println ("Your total charges are: " + chargesa);}

到

if (hours <= 10) { 
  System.out.println ("Your total charges are: " + chargesa);}

Answer 6

从看着它，

if (choice == 'A')
if (hours <= 10) {

这两个没有缩进，意味着无论第一个语句的结果如何，if (hours <= 10) {都会运行。因此，当用户键入B，然后输入小时数（小于10）时，第一个语句将显示false，第二个语句将显示true，因此运行该语句

尝试将{}放在所有if语句周围，然后再次尝试运行它。

我可能不正确。

如果其他说法不起作用 - 为什么？

6 个答案: