如何使数字无效

Question

创建一个名为minusSentinel2的新程序。

提示用户输入1到100之间的整数。允许用户输入任意数量的数字。

如果输入了无效的数字，打印“无效输入”再次提示用户，直到输入有效的数字。

输入 -1 后，程序停止并打印输入的最大数字，并显示文本“输入的最大数字是：”

我在“无效输入”上遇到了一些麻烦部分。当我键入大于100的数字时，“无效输入”不会被打印出来。我该如何解决这个问题？谢谢大家！

import java.util.*;
public class minusSentinel2
{
    public static void main (String[] args)
    {
        Scanner console = new Scanner(System.in);
        System.out.println("Enter a number between 1-100 (type -1 to quit):");
        int number = console.nextInt();
        int max = number;
        if (number < 1 && number > 100)//chekcs if value is valid
        {
            System.out.println("Invalid entry.");
            System.out.println("Enter a number between 1-100 (type -1 to quit).");
            console.next();
        }
        while (number != -1)
        {
            number = console.nextInt();
            if (number > max)
            {
                max = number;
            }
        }
        System.out.print("The largest number entered is: " + max);
    }
}

Answer 1

首先，我建议你不要复制和粘贴我们要求你做的，而只是用必要的部分为我们重新制定。

对于您的问题，此条件是错误的:

if (number < 1 && number > 100)

它对应于“小于1且大于100”。

因此，代替< code >

if (number < 1 || number > 100) {
   // it's not valid because lower than 1 or greater than 100
}

最后，你所做的似乎还有另一个问题。如果您输入了一个无效的数字，它将只再次询问一次，而不是相同的新值。因此，我建议您像这样使用while循环：

int number = 0;
while(number < 1 || number > 100) {
    number = console.nextInt();
    if (number < 1 || number > 100) {
        System.out.println("Invalid entry.");
        System.out.println("Enter a number between 1-100 (type -1 to quit).");
    }
}
int max = number;

最后，这是完整的代码:

Scanner console = new Scanner(System.in); // create scanner
int number = 0; // create new variable that will be used outside of while loop
while (number < 1 || number > 100) { // while the number isn't valid
    System.out.println("Enter a number between 1-100 (type -1 to quit):");
    number = console.nextInt(); // wait for user input
    if (number == -1) { // stop program
        console.close();
        return;
    } else if (number < 1 || number > 100) { // number invalid
        System.out.println("Invalid entry.");
    }
}

System.out.println("Now enter all number that you want. End with -1.");

int max = number; // create new max value
while (number != -1) {
    number = console.nextInt();
    if (number < 1 || number > 100) { // number invalid
        System.out.println("Invalid entry.");
    } else if (number > max) { // if number is upper than current one
        max = number;
        // here you can do something like that:
        // System.out.println("New max value: " + max);
    } else {
        // the value is value but not upper than current one, so we can write:
        // System.out.println("This value isn't upper to " + max);
    }
}
System.out.print("The largest number entered is: " + max);
console.close();