为什么mathGPA不能正常工作？

Question

我正在努力制作GPA计算器。 我试图解决的第一件事就是每个班级的个人GPA，经过计算，将累加到平均成绩点。 我定义了两个变量（mathGPA和historyGPA）mathGPA工作正常，直到我添加了historyGPA。 我现在担心，随着项目的进展，以前编码的个人GPA分数将无法被Java识别。 这是代码：

package problemset.leveltwo;

import java.util.*;

public class gpaCalculator {

public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);

    // A+
    double a = 4.00;

    // A-
    double b = 3.70;

    // B+
    double c = 3.30;

    // B
    double d = 3.00;

    // B-
    double e = 2.70; 

    // C+
    double f = 2.30;

    // C
    double g = 2.00;

    // C-
    double h = 1.70;

    // D+
    double i = 1.30;

    // D
    double j = 1.00;

    // D-
    double k = 0.70;

    // F
    double l = 0;

    System.out.println("Enter Your Math Grade (percentage)");
    int mathGrade = scanner.nextInt();

    System.out.println("Enter Your History Grade (percentage)");
    int historyGrade = scanner.nextInt();

    System.out.println("Enter Your English Grade (percentage)");
    int englishGrade = scanner.nextInt();

    System.out.println("Enter Your Science Grade (percentage)");
    int scienceGrade = scanner.nextInt();

    System.out.println("Enter Your Language Grade (percentage)");
    int languageGrade = scanner.nextInt();


    // MATH GRADE

    // Math = A
    if (mathGrade >= 96) {
        System.out.println("Math GPA = " + a);
        double mathGPA = 4.00;
        }

    // Math = A-
    if (mathGrade < 96) {
        if (mathGrade >= 90) {
            System.out.println("Math GPA = " + b);
            double mathGPA = 3.70;
        }
    }

    // Math B+
    if (mathGrade < 90) {
        if (mathGrade >= 86) {
            System.out.println("Math GPA = " + c);
            double mathGPA = 3.30;
        }
    }

    // Math B
    if (mathGrade < 86) {
        if (mathGrade >= 84) {
            System.out.println("Math GPA = " + d);
            double mathGPA = 3.00;
        }
    }

    // Math B-
    if (mathGrade < 84) {
        if (mathGrade >= 80) {
            System.out.println("Math GPA = " + e);
            double mathGPA = 2.70;
        }
    }

    // Math C+
    if (mathGrade < 80) {
        if (mathGrade >= 76) {
            System.out.println("Math GPA = " + f);
            double mathGPA = 2.30;
        }
    }

    // Math C
    if (mathGrade < 76) {
        if (mathGrade >= 73) {
            System.out.println("Math GPA = " + g);
            double mathGPA = 2.00;
        }
    }

    // Math C-
    if (mathGrade < 73) {
        if (mathGrade >= 70) {
            System.out.println("Math GPA = " + h);
            double mathGPA = 1.70;
        }
    }

    // Math D+
    if (mathGrade < 70) {
        if (mathGrade >= 66) {
            System.out.println("Math GPA = " + i);
            double mathGPA = 1.30;
        }
    }

    // Math D
    if (mathGrade < 66) {
        if (mathGrade >= 63) {
            System.out.println("Math GPA = " + j);
            double mathGPA = 1.00;
        }
    }

    // Math D-
    if (mathGrade < 63) {
        if (mathGrade >= 50) {
            System.out.println("Math GPA = " + k);
            double mathGPA = 0.70;
        }
    }

    // Math F
    if (mathGrade < 50) {
        System.out.println("Math GPA = " + 0);
        double mathGPA = 0.00;
    }



    // HISTORY GRADE

    // History = A
    if (historyGrade >= 96) {
        System.out.println("History GPA = " + a);
        double historyGPA = 4.00;
        }

    // History = A-
    if (historyGrade < 96) {
        if (historyGrade >= 90) {
            System.out.println("History GPA = " + b);
            double historyGPA = 3.70;
        }
    }

    // History B+
    if (historyGrade < 90) {
        if (historyGrade >= 86) {
            System.out.println("History GPA = " + c);
            double historyGPA = 3.30;
        }
    }

    // History B
    if (historyGrade < 86) {
        if (historyGrade >= 84) {
            System.out.println("History GPA = " + d);
            double historyGPA = 3.00;
        }
    }

    // History B-
    if (historyGrade < 84) {
        if (historyGrade >= 80) {
            System.out.println("History GPA = " + e);
            double historyGPA = 2.70;
        }
    }

    // History C+
    if (historyGrade < 80) {
        if (historyGrade >= 76) {
            System.out.println("History GPA = " + f);
            double historyGPA = 2.30;
        }
    }

    // History C
    if (historyGrade < 76) {
        if (historyGrade >= 73) {
            System.out.println("History GPA = " + g);
            double historyGPA = 2.00;
        }
    }

    // History C-
    if (historyGrade < 73) {
        if (historyGrade >= 70) {
            System.out.println("History GPA = " + h);
            double historyGPA = 1.70;
        }
    }

    // History D+
    if (historyGrade < 70) {
        if (historyGrade >= 66) {
            System.out.println("History GPA = " + i);
            double historyGPA = 1.30;
        }
    }

    // History D
    if (historyGrade < 66) {
        if (historyGrade >= 63) {
            System.out.println("History GPA = " + j);
            double historyGPA = 1.00;
        }
    }

    // History D-
    if (historyGrade < 63) {
        if (historyGrade >= 50) {
            System.out.println("History GPA = " + k);
            double historyGPA = 0.70;
        }
    }

    // History F
    if (historyGrade < 50) {
        System.out.println("History GPA = " + 0);
        double historyGPA = 0;


double total = mathGPA + historyGPA;
System.out.println("Total GPA = " + total);


        }

        }

}

Java Eclipse给出的错误消息是“mathGPA无法解析为变量”。 我不知道我写错了什么，但我希望有人可以给我一些洞察力来纠正我的代码。

Answer 1

正如所指出的，你在if语句中定义了mathgpa，所以它只存在于那里。

在if语句之前为它定义一个double，并消除冗余。

接下来学会使用if..then..else让生活更美好

如果您查看本教程中的最后一个示例，请提供帮助

http://docs.oracle.com/javase/tutorial/java/nutsandbolts/if.html

基本上做一个如果它不匹配使用其他如果直到你到达将匹配的最终其他

if (grade > 90) {
   // A
} else if (grade > 80) {
   // B
} else {
  // F
}

所以B是小于90且大于80而小于80的是F.