Question

如果用户输入了错误的字符，例如＆＃34; E＆＃34;或＆＃34; A＆＃34;在我的程序中如何向用户输出消息？我在我的程序中谈到的那条线是当用户必须选择输入三个字符P，M或D中的一个时。但是，如果用户输入了另一个没有列出的字符，我想要显示信息的程序。

正如您所看到的，用户输入＆＃34; E＆＃34;程序跳到下一步。但是，我希望用户得到通知并再次要求输入正确的值，即＆＃34; P，M或D＆＃34; 。

为了做我想要实现的目标，我相信我需要做一个if语句，所以我在这里尝试过。

if((i = P,M,D) && (i < ?)) {
   System.out.println("ERROR, please input only P,M or D.");
}

Screenshot of the program

JAVA CODE

String grade;
int yr2cred[] = new int[18];
char yr2grade[] = new char[18];
for (int i = 1; i <= 18; i++) {
    System.out.println("Please enter your grade for unit " + i +" "+(username) + ".");
    grade = userinput.next();
    yr2grade[i - 1] = grade.charAt(0);
    if (yr2grade[i - 1] == 'P' || yr2grade[i - 1] == 'p') {
        yr2cred[i - 1] = yr2cred[i - 1] + P;
    }
    if (yr2grade[i - 1] == 'M' || yr2grade[i - 1] == 'm') {
        yr2cred[i - 1] = yr2cred[i - 1] + M;
    }
    if (yr2grade[i - 1] == 'D' || yr2grade[i - 1] == 'd') {
        yr2cred[i - 1] = yr2cred[i - 1] + D;
    }
}

Answer 1

可能的代码在这里。我们迭代单位，对于我们要求输入等级值的每个单位，直到输入有效单位。最后打印成绩列表。

import java.util.Arrays;
import java.util.Scanner;

public class CheckInput {
    public static void main(String[] args) {

        int unitsCount = 18;
        String[] unitGrades = new String[unitsCount];

        String grade;

        Scanner userInput = new Scanner(System.in);

        for (int i = 0; i < unitsCount; i++) {
            grade = "";
            while ( ! (grade.equalsIgnoreCase("P") || grade.equalsIgnoreCase("M") || grade.equalsIgnoreCase("D") ) ) {
                if (!"".equals(grade)){
                    System.out.println("ERROR, please input only P,M or D.");
                }
                System.out.print("Please enter your grade for unit " + i + ": ");
                grade = userInput.next();
            }
            unitGrades[i] = grade;
        }
        System.out.println("Unit grades: "+Arrays.toString(unitGrades));
    }
}

Answer 2

您可以在 for 循环中使用 while 循环执行此操作：

for (int i = 1; i <= 18; i++) {
    while (grade.equals("")) {
        System.out.println("Please enter your grade for unit " + i + " " + username + ".");
        grade = userinput.next().toLowerCase();
        yr2grade[i - 1] = grade.charAt(0);
        if (yr2grade[i - 1] == 'p') {
            yr2cred[i - 1] = yr2cred[i - 1] + P;
        } else if (yr2grade[i - 1] == 'm') {
            yr2cred[i - 1] = yr2cred[i - 1] + M;
        } else if (yr2grade[i - 1] == 'd') {
            yr2cred[i - 1] = yr2cred[i - 1] + D;
        } else {
            System.err.println("Invalid Grade Supplied! Try Again.\n");
            grade = "";
        }
    }
    grade = "";
}

如果用户输入无效字符，我如何让我的程序向用户输出消息？

2 个答案: