java - 为什么当我运行程序时，会显示代码中的所有字母等级选项？我只想显示正确答案

Question

我对 Java 编程非常陌生，有人告诉我这是一个很棒的网站，可以将我推向正确的方向。

为什么当我运行程序时，会显示代码中的所有字母等级选项？我只想显示正确的一个。请帮忙。

另外，当输入时，如何让数值显示在同一行而不返回到下一行？

感谢您对 Java 新手的帮助和见解。

/*
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 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package assignment_1;

/**
 *
 * @author 
 */

import java.util.Scanner;
public class Assignment_1 
{

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) 
    {
        System.out.println("Welcome to the Letter Grade Convertor Program");
        System.out.println();

        Scanner sc = new Scanner(System.in);

        String choice = "y";
        while (choice.equalsIgnoreCase("y"))
        {

            System.out.println("Enter numerical grade: ");
            int grade = sc.nextInt();
            char letter = 0;
            if(grade <= 100 || grade >= 90)
                letter = 'A';
                System.out.println("Letter grade: " + letter);
            if (grade <= 89 || grade >= 80)
                letter = 'B';
                System.out.println("Letter grade: " + letter);

            if (grade <= 79 || grade >= 70)
                letter = 'C';
                System.out.println("Letter grade: " + letter);

            if(grade <= 69 || grade >= 60)
                letter = 'D';
                System.out.println("Letter grade: " + letter);

            if(grade < 60 || grade <=0)
                letter = 'F';
                System.out.println("Letter grade: " + letter);


            System.out.println("Continue? (y/n): ");
            choice = sc.next();
            System.out.println();
        }
    }
}

Answer 1

如果有多个语句，则应添加大括号。如果您留下括号，则只有第一行属于 if 条件。因此 sout 代码始终会执行。当您添加卷闸时，它是一个 block ，其中的所有行都属于 if 条件。

if(grade <= 100 || grade >= 90){
     letter = 'A';
     System.out.println("Letter grade: " + letter);
}

始终添加大括号是一个好的做法

但是，正如 @dici 建议您可以在最后打印成绩，而不是在所有 if 条件中添加 out.print

像这样

public static void main(String[] args) {
    System.out.println("Welcome to the Letter Grade Convertor Program");
    System.out.println();

    Scanner sc = new Scanner(System.in);

    String choice = "y";
    while (choice.equalsIgnoreCase("y")) {

        System.out.println("Enter numerical grade: ");
        int grade = sc.nextInt();
        char letter = 0;
        if (grade <= 100 || grade >= 90) {
            letter = 'A';
        }

        if (grade <= 89 || grade >= 80) {
            letter = 'B';
        }

        if (grade <= 79 || grade >= 70) {
            letter = 'C';
        }

        if (grade <= 69 || grade >= 60) {
            letter = 'D';
        }

        if (grade < 60 || grade <= 0) {
            letter = 'F';
        }
        System.out.println("Letter grade: " + letter);

        System.out.println("Continue? (y/n): ");
        choice = sc.next();
        System.out.println();
    }
}