如何在Java中使用for循环减去n个数字？

Question

当我使用for循环进行减法时，我没有得到正确的输出。

我应该在代码中应用什么逻辑才能使用for循环正确地减去？

由于我是JAVA的新手，请帮助我。

我的代码如下：

import java.io.*;
import java.util.*;

class Sub
{
    public static void main(String args[])
    {
        Scanner s=new Scanner(System.in);
        int a,n,i;
        String yn;
        boolean loop=true;

        while(loop)
        {
            try
            {
                do
                {
                    loop=true;
                    System.out.println("Enter how many numbers to Subtract?: ");
                    n=s.nextInt();
                    int sum=0;
                    for(i=1;i<=n;)
                    {
                        try
                        {
                            System.out.println("Enter number "+i+" : ");
                            a=s.nextInt();
                            sum=a-sum;
                            i++;
                        }
                        catch(Exception e)
                        {
                            System.out.println("Invalid Entry. Try again!!");
                        }
                    }
                    System.out.println("Answer is:"+sum);
                    System.out.println("Do you want to continue?(Y/N): ");
                    yn=s.next();
                    loop=yn.equals("Y")||yn.equals("y");
                }while(loop);
            }
            catch(Exception e)
            {
                System.out.println("Re-enter the Limit");
            }
        }

    }
}

Answer 1

您应该以sum作为第一个数字（而不是零）开始，然后从中减去其余的数字：

    loop=true;
    System.out.println("Enter how many numbers to Subtract?");
    n=s.nextInt();
    int sum=0;
    for(i=1;i<=n;)
    {
        try
        {
            System.out.println("Enter number "+i+" : ");
            a=s.nextInt();
            sum=a-sum;
            i++;
        }
        catch(Exception e)
        {
            System.out.println("Invalid Entry. Try again!!");
        }
    }

至：

...
loop = true;
System.out.println("Enter how many numbers to Subtract?: ");
n = s.nextInt();
System.out.println("Enter number 1 : ");
int sum = s.nextInt();
for (int i=2; i <= n; i++) {
    try {
        System.out.println("Enter number " + i + " : ");
        a = s.nextInt();
        sum -= a;
    } catch (Exception e) {
        System.out.println("Invalid Entry. Try again!!");
    }
}
...

此外，除了做：

yn.equals("Y") || yn.equals("y")

您可以使用equalsIgnoreCase() ：

yn.equalsIgnoreCase("Y")

最后，您应该对变量使用有意义的名称（即使是一个很小的程序，也建议您养成良好的习惯），因此，不要使用：

    int a, n, i; // you can define and use i inside the for-loop - no need to define it outside
    String yn;

考虑使用更具表现力的名称，例如：

    int inputNumber, numberOfVariables;
    String continueLooping;

---

以下版本可以改进（甚至可以进一步重构）：

public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);
    while (true) {
        int numOfArguments = getNumberOfArguments(scanner);
        int sum = getNextNumberFromUser(scanner, 1);
        for (int i = 2; i <= numOfArguments; i++) {
            sum -= getNextNumberFromUser(scanner, i);
        }
        System.out.println("Answer is: " + sum + "\n\nDo you want to continue?(Y/N): ");
        String runAgain = scanner.next();
        if (runAgain.equalsIgnoreCase("N")) {
            break;
        }
    }
}

private static int getNextNumberFromUser(Scanner scanner, int i) {
    while (true) {
        try {
            System.out.println("Enter number " + i + " : ");
            return scanner.nextInt();
        } catch (InputMismatchException e) {
            System.out.println("Invalid Entry. Try again!!");
            scanner.nextLine();
        }
    }
}

private static int getNumberOfArguments(Scanner scanner) {
    int numberOfArguments = -1;
    System.out.println("Enter how many numbers to Subtract?: ");
    while (numberOfArguments == -1) {
        try {
            numberOfArguments = scanner.nextInt();
            if (numberOfArguments <= 0) {
                numberOfArguments = -1;
            }
        } catch (InputMismatchException e) {
            System.out.println("Illegal number of arguments to subtract, please try again: ");
            scanner.nextLine();
        }
    }
    return numberOfArguments;
}