Question

我试图对涉及变量的公式进行简单的数学计算。但是，编译器中会弹出一个错误，指示变量类型不匹配。我已经尝试过转换和更改变量类型，但它们不起作用。如何解决这个问题而不破坏我的代码的基本格式。

我没有Java经验，所以任何指针都会有所帮助。

这是代码。这是一个货币兑换计划。错误发生在代码的第二部分，即else部分。

import java.util.Scanner;
public class MConvert
{
    public static void main (String[] args)
   {
     int penny, nickel, dime, quarter, halfDollar, dollar, fiveDollar, tenDollar,     twentyDollar, fiftyDollar, hundredDollar; 
     //can sub $ sign for dollar in variable, convention otherwise
     double totalMoney; 
     Scanner scan = new Scanner (System.in);
        System.out.println ("Are you converting to the total? If so, type true. \nIf you are converting from the total, then type false.");
       boolean TotalorNot = true;
        TotalorNot = scan.nextBoolean();


       if (TotalorNot) {

        System.out.println ("Type in the number of one-hundred dollar bills.");
        hundredDollar = scan.nextInt();
        System.out.println ("Type in the number of fifty dollar bills.");
        fiftyDollar = scan.nextInt();
        System.out.println ("Type in the number of twenty dollar bills.");
        twentyDollar = scan.nextInt();
        System.out.println ("Type in the number of ten dollar bills.");
        tenDollar = scan.nextInt();
        System.out.println ("Type in the number of five dollar bills.");
        fiveDollar = scan.nextInt();
        System.out.println ("Type in the number of one dollar bills or coins.");
        dollar = scan.nextInt();
        System.out.println ("Type in the number of half-dollar coins.");
        halfDollar = scan.nextInt();
        System.out.println ("Type in the number of quarter-dollar coins.");
        quarter = scan.nextInt();
        System.out.println ("Type in the number of dimes.");
        dime = scan.nextInt();
        System.out.println ("Type in the number of nickels.");
        nickel = scan.nextInt();
        System.out.println ("Type in the number of pennies coins.");
        penny = scan.nextInt();
        totalMoney = (hundredDollar * 100) + (fiftyDollar * 50) + (twentyDollar * 20) + (tenDollar * 10) + (fiveDollar * 5) + (dollar * 1) + ((double)halfDollar * 0.5) + ((double)quarter * 0.25) + ((double)dime * 0.1) + ((double)nickel * 0.05) + ((double)penny * 0.01); 
    System.out.println ("Here is total monetary value of the bills and coins you entered: " + totalMoney);




}    else {

        System.out.println ("Type in the total monetary value:");
        totalMoney = scan.nextDouble();
        hundredDollar = ((int)totalMoney / 100);
        fiftyDollar = ((int)totalMoney - (hundredDollar * 100)) / 50;
        twentyDollar = ((int)totalMoney - (fiftyDollar * 50)) / 20;
        tenDollar = ((int)totalMoney - (twentyDollar * 20)) / 10;
        fiveDollar = ((int)totalMoney - (tenDollar * 10)) / 5;
        dollar = ((int)totalMoney - (fiveDollar * 5)) / 1;
        (double) halfDollar = (totalMoney - (dollar * 1)) / 0.5;
        quarter = ((int)totalMoney - (halfDollar * 0.5)) / 0.25;
        dime = ((int)totalMoney - (quarter * 0.25)) / 0.1;
        nickel = ((int)totalMoney - (dime * 0.1)) / 0.05;
        penny = ((int)totalMoney - (nickel * 0.05)) / 0.01;

        System.out.println (hundredDollar + " hundred dollar bills");
        System.out.println (fiftyDollar + " fifty dollar bills");
        System.out.println (twentyDollar + " twenty dollar bills");
        System.out.println (tenDollar + " ten dollar bills");
        System.out.println (fiveDollar + " five dollar bills");
        System.out.println (dollar + " one dollar bills or coins");
        System.out.println (halfDollar + " half-dollar coins");
        System.out.println (quarter + " quarter-dollar coins");
        System.out.println (dime + " dimes");
        System.out.println (nickel + " nickel");
        System.out.println (penny + " penny");

    }


}

}

Answer 1

(double) halfDollar = (totalMoney - (dollar * 1)) / 0.5;

完全错误，首先删除此说明。

还可以使用以下行更改您的代码。

quarter = (int)((totalMoney - (halfDollar * 0.5)) / 0.25);
dime = (int) ((totalMoney - (quarter * 0.25)) / 0.1);
nickel =(int)( (totalMoney - (dime * 0.1)) / 0.05);
penny = (int)((totalMoney - (nickel * 0.05)) / 0.01);

您还需要改进代码的逻辑，我可以清楚地看到它不能满足您的目标。

Answer 2

在这一行（（int）totalMoney - （tenDollar * 10））/ 5;

演员表仅应用于totalMoney

要转换整个表达式的值，你必须这样做

(int)(totalMoney - (tenDollar * 10)) / 5);

Answer 3

问题出在以下几行：

(double) halfDollar = (totalMoney - (dollar * 1)) / 0.5;

这里(double)的含义是什么？您不能将变量赋值的左侧（变量本身）强制转换为double。该变量被声明为int，并且无法更改。从不。

这一行编译（但可能与语义不一致）：

halfDollar = (int) ((totalMoney - (dollar * 1)) / 0.5);

除此之外：我不认为，程序会这样做，你想要它做什么......

Answer 4

(double) halfDollar = (totalMoney - (dollar * 1)) / 0.5;

你想通过halfDollar上的双重演员实现什么？首先删除它。我花了5分钟才找出你的代码中有这么多红线的原因。

接下来，你可以做一个这样的简单案例： -

halfDollar = (int)((totalMoney - (dollar * 1)) / 0.5);

但不建议将双值转换为int，因为您可能会丢失大量的十进制数据。为什么不简单地将所有penny, nickel, dime, quarter, halfDollar, dollar, fiveDollar, tenDollar,twentyDollar, fiftyDollar, hundredDollar;作为double本身？

Java中的Casting或Variable类型错误

4 个答案: