用户输入问题的代码双精度方程错误

Question

我的第一个任务是开发一个代码，允许用户输入他们希望行驶的距离、燃油效率和汽油成本的数据。然后创建一个代码以计算旅行的总费用。

我有所有输入值的所有代码，但我在等式本身方面遇到了问题。Java 无法识别 "/"。我无法理解我在做什么，除非我需要添加更多代码以使等式正常工作。

import java.util.Scanner;
public class DrivingCost
{
    public static void main(String args[])
    {
        Scanner s = new Scanner(System.in);
        System.out.print("Please enter your distance (miles): ");
      Scanner t = new Scanner(System.in);
      System.out.print("Please enter vehicle's fuel efficiency (mpg): ");
      Scanner u = new Scanner(System.in);
      System.out.print("Please enter the price per gallon (dollars): ");
      String distanceInMiles = s.nextLine();
      System.out.println("The distance (miles): " + distanceInMiles);
      String fuelEfficiency = t.nextLine();
      System.out.println("Fuel efficiency (mpg):" + fuelEfficiency);
        String pricePerGallon = u.nextLine();
        System.out.println("Price per gallon (dollars): " + pricePerGallon);
      double tripCost = (distanceInMiles / fuelEfficiency) * pricePerGallon;
      System.out.println("The trip cost (dollars): " + tripCost);
    }
} 

这是我不断收到的错误：

DrivingCost.java:32: error: bad operand types for binary operator '/'
  double tripCost = (distanceInMiles / fuelEfficiency) * pricePerGallon;
                                     ^

Answer 1

您
1. 正在对字符串进行数学运算，您不能，您需要double类型
   • Double.parseDouble(sc.nextLine());读取一行并解析为double（好处：一般避免返回线错误，养成好习惯）
   • sc.nextDouble()直接读取double
2. 每个源仅使用一个扫描仪
3. 在print和扫描仪询问之间有一个良好的顺序

Scanner sc = new Scanner(System.in);
System.out.print("Please enter your distance (miles): ");
String distanceInMiles = Double.parseDouble(sc.nextLine());
System.out.println("The distance (miles): " + distanceInMiles);
System.out.print("Please enter vehicle's fuel efficiency (mpg): ");
String fuelEfficiency = Double.parseDouble(sc.nextLine());
System.out.println("Fuel efficiency (mpg):" + fuelEfficiency);
System.out.print("Please enter the price per gallon (dollars): ");
String pricePerGallon = Double.parseDouble(sc.nextLine());
System.out.println("Price per gallon (dollars): " + pricePerGallon);
double tripCost = (distanceInMiles / fuelEfficiency) * pricePerGallon;
System.out.println("The trip cost (dollars): " + tripCost);

Answer 2

您正在尝试使用字符串进行计算。您必须解析字符串输入中的双精度。只需将等式线更改为以下内容：

double tripCost = (Double.valueOf(distanceInMiles) / Double.valueOf(fuelEfficiency)) * Double.valueOf(pricePerGallon);

附言正确的输入验证将是一个很好的改进。如果用户提供不正确的输入。另外，如评论中所述，无需使用多个Scanners。一个就足够了。

Answer 3

您可以使用

s.nextDouble()在double中获得distanceInMiles，fuelEfficiency和pricePerGallon。之后，您应该能够对这些变量执行double操作。

public static void main(String args[])
  {
    Scanner s = new Scanner(System.in);
    System.out.print("Please enter your distance (miles): ");
    double distanceInMiles = s.nextDouble();
    System.out.println("The distance (miles): " + distanceInMiles);
    System.out.print("Please enter vehicle's fuel efficiency (mpg): ");
    double fuelEfficiency = s.nextDouble();
    System.out.println("Fuel efficiency (mpg):" + fuelEfficiency);
    System.out.print("Please enter the price per gallon (dollars): ");
    double pricePerGallon = s.nextDouble();
    System.out.println("Price per gallon (dollars): " + pricePerGallon);
    double tripCost = (distanceInMiles / fuelEfficiency) * pricePerGallon;
    System.out.println("The trip cost (dollars): " + tripCost);
  }