将这些应考虑的幻数？ [英] Would These Be Considered Magic Numbers?

问题描述

我刚刚完成了编写程序的编程类，我想避免使用幻数，所以这里是我的问题：

I've just completed writing a program for a programming class, and I want to avoid use of magic numbers, so here's my question:

在下面的功能，将我的数组索引被视为神奇数字？

In the function below, would my array indexers be considered magic numbers?

code：

string CalcGrade(int s1, int s2, int s3, double median)
{
const int SIZE = 23;
const int LETTER_GRADE_BARRIERS[SIZE] = { 400, 381, 380, 361, 360, 341, 340, 321, 320, 301, 300, 281, 280, 261, 260, 241, 240, 221, 220, 201, 200, 181, 180 }; 
double finalGrade;
string letterGrade;

finalGrade = s1 + s2 + s3 + median;

if (finalGrade >= LETTER_GRADE_BARRIERS[1] && finalGrade <= LETTER_GRADE_BARRIERS[0])
{
    letterGrade = "A";
}
else if (finalGrade >= LETTER_GRADE_BARRIERS[3] && finalGrade <= LETTER_GRADE_BARRIERS[2])
{
    letterGrade = "A-";
}
else if (finalGrade >= LETTER_GRADE_BARRIERS[5] && finalGrade <= LETTER_GRADE_BARRIERS[4])
{
    letterGrade = "B+";
}
else if (finalGrade >= LETTER_GRADE_BARRIERS[7] && finalGrade <= LETTER_GRADE_BARRIERS[6])
{
    letterGrade = "B";
}
else if (finalGrade >= LETTER_GRADE_BARRIERS[9] && finalGrade <= LETTER_GRADE_BARRIERS[8])
{
    letterGrade = "B-";
}
else if (finalGrade >= LETTER_GRADE_BARRIERS[11] && finalGrade <= LETTER_GRADE_BARRIERS[10])
{
    letterGrade = "C+";
}
else if (finalGrade >= LETTER_GRADE_BARRIERS[13] && finalGrade <= LETTER_GRADE_BARRIERS[12])
{
    letterGrade = "C";
}
else if (finalGrade >= LETTER_GRADE_BARRIERS[15] && finalGrade <= LETTER_GRADE_BARRIERS[14])
{
    letterGrade = "C-";
}
else if (finalGrade >= LETTER_GRADE_BARRIERS[17] && finalGrade <= LETTER_GRADE_BARRIERS[16])
{
    letterGrade = "D+";
}
else if (finalGrade >= LETTER_GRADE_BARRIERS[19] && finalGrade <= LETTER_GRADE_BARRIERS[18])
{
    letterGrade = "D";
}
else if (finalGrade >= LETTER_GRADE_BARRIERS[21] && finalGrade <= LETTER_GRADE_BARRIERS[20])
{
    letterGrade = "D-";
}
else if (finalGrade <= LETTER_GRADE_BARRIERS[22])
{
    letterGrade = "Fail";
}

return letterGrade;
}

谢谢！

推荐答案

是的，任何数量比-1,0或1的可能是一个神奇的数字。

Yes, any number other than -1,0 or 1 is probably a magic number.

除非你是一个真正的大师，那么你很可能获准使用的两个大国自由，以及： - ）

Unless you're a real guru, then you're probably allowed to use powers of two freely as well :-)

顺便说一句，你很可能重构了code是一个小更易于理解，是这样的：

As an aside, you could probably refactor that code to be a little more understandable, something like:

string CalcGrade (int s1, int s2, int s3, double median) {
    // Grade lookup arrays. If grade is >= limit[n], string is grades[n].
    // Anything below D- is a fail.
    static const int Limits[] = {400, 380, 360, 340,320, 300, 280,260, 240, 220,200,180 }; 
    static const int Grades[] = {"A+","A","A-","B+","B","B-","C+","C","C-","D+","D","D-"};

    double finalGrade = s1 + s2 + s3 + median;

    // Check each element of the array and, if the final grade is greater
    //   than or equal to, return the grade string.
    for (int i = 0; i < sizeof(Limits) / sizeof(*Limits); i++)
        if (finalGrade >= Limits[i])
            return Grades[i];

    // Otherwise, failed.
    return "Fail";
}

这消除了魔术时S $ P $垫遍布code到这是显而易见的，他们是如何工作的地区（假设你对准他们很好）。

This removes the magic numbers spread all over the code to an area where it's immediately obvious how they work (assuming you align them nicely).

这也与原来的解决方案中删除一个问题，因为什么，我们与别人，达到380.5分做 - 这不是的真正的公平失败:-)或者那些的BOD分配一个档次，来的400以上（因为似乎没有要回的方式A +）。

It also removes a problem with your original solution as to what we do with someone that achieved a score of 380.5 - it's not really fair to fail those bods :-) Or to assign a grade to "" to those above 400 (since there doesn't appear to be a way to return "A+").

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