期望的输出计算错误？

Question

我已经编写了这个程序，但是在编译时遇到了一个逻辑错误。

我的输入是1, 2, 6, 10，用于选择产品，同时输出应该是

Total items ordered: 3
Price of items ordered: $747.00
Sales Tax: $48.55
Total amount due: $795.55

奇怪的是它给了我

Total items ordered: 3
Price of items ordered: $6611.00
Sales Tax: $429.715
Total amount due: $7040.715 

我的 for 循环条件或计算中是否存在错误，或者我的数组是否存在导致这种过度膨胀的输出？

import java.util.Scanner;
public class GrapefruitOrderingArray {

//Declare Constants 
public static final int SIZE = 100;
public static final int[] itemPrices = {49,299,329,399,199,1299,1199,999,599};  

public static void main(String[] args) {
// Declare Variables
    Scanner input = new Scanner (System.in);                                    
    String CustomerName;                                                       
    int[] naNumber = new int [SIZE];                                            
    int nProducts = 0;                                                        
    double nTotal = 0;                                                          
    double dFinalPrice = 0.0;                                                   
    int nCount = 0;                                                             

    //Declare Constants 
    final int SENTINEL = 10;   
    final double SALES_TAX = 0.065;

    //Prompt user to enter name
    System.out.println("Please enter your name: ");

    //Enter user name
    CustomerName = input.nextLine();

    System.out.println("");

    //Begin Product Listing Declarations with respect to array above
    System.out.println("GRAPEFRUIT PRODUCT:");
    System.out.println("1. gPod shuffle $" + itemPrices[0]);
    System.out.println("2. gPod Touch   $" + itemPrices[1]);
    System.out.println("3. gPad Mini    $" + itemPrices[2]);
    System.out.println("4. gPad 2       $" + itemPrices[3]);
    System.out.println("5. gPhone       $" + itemPrices[4]);
    System.out.println("6. gMac         $" + itemPrices[5]);
    System.out.println("7. MacNovel Pro $" + itemPrices[6]);
    System.out.println("8. MacNovel Air $" + itemPrices[7]);
    System.out.println("9. MiniMac      $" + itemPrices[8]);
    System.out.println("10. Complete my order");

    //Keep reading until the input is terminated by sentinel
    System.out.println("\nPlease select an item from the menu above: ");

    //Read number entered by the user
    naNumber[nCount] = input.nextInt();

    //Begin while-loop statement
    while (naNumber[nCount] != SENTINEL) {

    System.out.println("\nPlease select another item from the menu above: ");

    nCount++;

    //Read number entered by the user
    naNumber[nCount] = input.nextInt();
 }  

    System.out.println("Thank you for ordering with Grapefruit Company, " + CustomerName);
        //Call final price calculation
        dFinalPrice = calculateTotalPrice(naNumber,itemPrices,nTotal);

            //Print blank line to screen
            System.out.println("");

            //Total amount of product ordered
            System.out.println("Total items ordered: " + nCount );

            //Total price of items ordered
            System.out.println("Price of items ordered: $" + dFinalPrice );

            //Sales tax associated with the purchase
            System.out.println("Sales tax: $" + SALES_TAX * dFinalPrice );

            //Total amount due by the customer to Grapefruit Co. 
            System.out.println("Total amount due: $" + (SALES_TAX * dFinalPrice + dFinalPrice ));
    } //End main method

 private static double calculateTotalPrice(int[] naNumber, int[] itemPrices) {

  double total = 0;

  //Calculate entered items
  for(int i = 0; i < naNumber.length; i++){
   if(naNumber[i] != 0) {
   total += itemPrices[naNumber[i] - 1];
  }
}

  return total;
  }
} //end class calculateTotalPriceOfItemsOrdered

Answer 1

naNumber 将包含从 1 到 9 的数字。这意味着您将在某些时候将商品价格乘以一些较大的数字，这就是为什么您会得到较大的总数。

我认为你想做的是

double itemTotal = itemPrices[naNumber[i] - 1];
nTotal += itemTotal;

没有将 itemPrices[i] 乘以 naNumber[i]

此外，您实际上并不需要将nTotal 传递给方法并在每个循环中初始化double。您可以在循环外声明一个字段：

double total = 0;

像这样在循环中使用它：

total += itemPrices[naNumber[i] - 1];

并在方法结束时返回。

所以你的方法看起来像这样：

private static double calculateTotalPrice(int[] naNumber, int[] itemPrices) {

double total = 0;

//Calculate entered items
for(int i = 0; i < naNumber.length; i++){
  if(naNumber[i] != 0) {
  total += itemPrices[naNumber[i] - 1];
  }
}

return total;
}

Answer 2

这里有三个问题。

• 您将标记值 10 放入用户选择的项目数组中。
• 您使用循环索引而不是用户在计算价格时选择的数字。
• 您将每件商品的价格乘以它的数量。所以用户购买了商品 6 中的 6 件。

在您的main 方法中，您需要将用户的输入读入另一个变量，如果它不是标记值，则仅将其插入到数组中。

在您的 calculateTotalPrice 方法中，您应该像这样计算单个订单项的价格：

double itemTotal = itemPrices[naNumber[i] - 1];