Question

因此对于Java编程来说，它仍然是新手，为此，我需要制作一个程序来计算自动售货机的更改。它基于25美分对1美元之间的5美分增量。对于此分配，如果我使用循环来强制用户在范围内输入值，我会获得额外的功劳，因为我本来是要抓挠的，因为我没有得到它，但很快我就重新使用了它。唯一的事情是我的条件之一，它创建了输出消息的无限循环，我不确定为什么。任何建议将不胜感激

/** Carmine A
The purpose of this program is to calculate the change to be dispensed from 
a vending machine */


//import scanner so user can input data
import java.util.Scanner;

public class lab2Test{

//declaration of variables to be used in program


float changeGiven;

    public static void main(String args[]) {
    //ties user input variable to class so scanner can use it
    int userInput;
    int itemCost;

        //initiates the keyboard to be used
        Scanner keyboard = new Scanner(System.in);

        //print statement to tell user how to enter price
        System.out.println("Enter price of item from 25 cents to a dollar in 5-cent increments \n"
                        + "Do not enter a decimal point");

    //user inputs value to be set to variable
    userInput= keyboard.nextInt();
    //System.out.println("You entered ." +userInput + " as the price");

    //while loop to make sure input stays in bounds
    while(userInput<25 || userInput>100){
        System.out.println("Invalid amount entered! \n"
                        + "Please enter an amount between 25 cents and 1 dollar");

                while(userInput>25 && userInput<100){
                System.out.println("Price is in bounds");
                System.out.println("Please enter a valid amount between 25-100");
                itemCost=keyboard.nextInt();
            }
}
itemCost=userInput;
//print out item cost based off users input
System.out.println("You enetered: " + itemCost +" as the items cost");

} }

更新

好，按照你们说的做，做这个

//while loop to make sure input stays in bounds
    while(userInput<25 || userInput>100){
        System.out.println("Invalid amount entered! \n"
                        + "Please enter an amount between 25 cents and 1 dollar");
        userInput=keyboard.nextInt();

                        }

感谢您的帮助！知道这有点愚蠢，但这就是为什么我寻求帮助，以便我可以学习

因此，我相信如果我为同一程序创建另一个线程，我将不予理so，因此我将添加到该线程中。

我几乎完成了我需要的一切，但遇到了一些问题。 1.由于某种原因，在我编译并运行我的代码“ Change Due：”后，由于两次打印，我不确定为什么会这样，因为我在print语句中只有一次，但是我可能会丢失它。 2.我需要以货币格式打印，由于某种原因，我尝试了不同的格式设置选项，但没有一个会变圆（我有这种感觉，但是由于第二次“更改到期日”打印而无法显示），但是可以是错的 3.在第55行上，我收到此消息，但不确定为什么C：\ Users \ finst \ Desktop \ Intro to Java \ Labs \ Lab2 \ lab2Test.java：55：错误：不兼容的类型：可能从双精度转换为int changeRemainder =（changeDue *（double）100）;

这是我目前拥有的： /** 胭脂红该程序的目的是计算要分配的更改自动售货机* /

//import scanner so user can input data
import java.util.Scanner;

public class lab2Test{

//declaration of variables to be used in program

    public static void main(String args[]) {
    //ties user input variable to class so scanner can use it
    double userInput;
    double itemCost;

        //initiates the keyboard to be used
        Scanner keyboard = new Scanner(System.in);

        //print statement to tell user how to enter price
        System.out.println("Enter price of item from 25 cents to a dollar in 
5-cent increments");


    //user inputs value to be set to variable
    userInput= keyboard.nextDouble();

    //while loop to make sure input stays in bounds
    while(userInput<(.25) || userInput>(1.00)){
        System.out.println("Invalid amount entered! \n"
                        + "Please enter an amount between 25 cents and 1 
dollar");
        userInput=keyboard.nextDouble();

                        }


//print out item cost based off users input
System.out.println("You entered: " + userInput +" as the items cost");
System.out.println("You entered a dollar to pay with");

//algorithm to calculate change due
int quarters;
int nickels;
int dimes;
int pennies;
int changeRemainder;
double changeDue;
double dollar=1;

//calculates change due
changeDue= (dollar - userInput);
//System.out.printf("%.2f" + "\n" ,changeDue);
//System.out.println("Change due:" + changeDue);

//makes the remainder into a number that can be used
changeRemainder= (changeDue*(double)100);

//calculates the amount of each coin needed to make the change
quarters= (changeRemainder / 25);
changeRemainder= changeRemainder % 25;

dimes= (changeRemainder/10);
changeRemainder= changeRemainder%10;

nickels=(changeRemainder/5);
changeRemainder= changeRemainder%5;

pennies=(changeRemainder);

//output statement to print coin amounts
System.out.println("Quarters: " + quarters);
System.out.println("Dimes: " + dimes);
System.out.println("Nickels: " + nickels);
System.out.println("Pennies: " + pennies);

} }

Answer 1

您不需要2个while循环；只有一个会做。无论如何，您的while循环都会检查'userInput'变量，但在while循环中永远不会改变；您将改为更新itemCost变量。

Answer 2

由于userInput永远不会在循环中更新，因此其值不会改变，并且有可能永远循环。

也许您的意思是userInput=keyboard.nextInt();，但无论如何您都不需要两个循环。

userInput=keyboard.nextInt();
while (userInput<25 || userInput>100) {
    System.out.println("Invalid amount entered! \n"
                    + "Please enter an amount between 25 cents and 1 dollar");
    userInput=keyboard.nextInt();
}

Answer 3

我将为您的while循环使用布尔值，并在其中创建if语句，以检查有效条目并计算更改。希望这会有所帮助！

boolean end = true;
while (end) {
   //retrieve user input of cost and assign value to variable 

   //create an if statement check if the value is valid
   if(itemCost >=25 && itemCost <=100){

      //retrieve user input for change entered

      //calculate change for the user and display it

      //end loop
      end = false;
   } else {  
      //invalid entry
      end = false;
   }
}

创建了两个条件的While循环，一个条件与另一个条件一样会导致无限循环

3 个答案: