C＃文件I / O效率

Question

I have done a homework assignment, here is the problem statement:

Your program should work as follows:

1. Ask the user to give you a file name. Get the file name and save it.
2. Open the file.
3. From the file read a temperature and a wind speed. Both values should be stored in variables declared as double. The file is a text file. Each line of the file contains a temperature and a wind speed value.

4. Calculate the wind chill factor using a programmer written method, and display the result in the form:

   For t = temperature from file and v = wind speed from file Wind chill index = calculated result degrees Fahrenheit.

   Show all numbers with two digits after the decimal point. (Remember-no magic numbers!)

5. Repeat these steps until an end of file is encountered.

I have completed the assignment, my code is below, I was just wondering if there was any way to make it more efficient, or if there are some different and creative ways to accomplish this problem, I already turned this in and got 50/50, but I'm just curious as to how some of you advanced and skilled programmers would approach this problem.

using System;
using System.IO;

class Program
{
    // declare constants to use in wind chill factor equation - no magic numbers
    const double FIRST_EQUATION_NUMBER = 35.74;
    const double SECOND_EQUATION_NUMBER = 0.6215;
    const double THIRD_EQUATION_NUMBER = 35.75;
    const double FOURTH_EQUATION_NUMBER = 0.4275;
    const double EQUATION_EXPONENT = 0.16;
    const int DEGREE_SYMBOL_NUMBER = 176;

    static void Main()
    {
        // declare and initialize some variables
        string filePath = "";
        string line = "";
        double temperature = 0.0;
        double windSpeed = 0.0;
        double windChillFactor = 0.0;
        char degreeSymbol = (char)DEGREE_SYMBOL_NUMBER;

        // ask user for a file path
        Console.Write("Please enter a valid file path: ");
        filePath = Console.ReadLine();

        // create a new instance of the StreamReader class
        StreamReader windChillDoc = new StreamReader(@filePath);

        // start the read loop
        do 
        {
            // read in a line and save it as a string variable
            line = windChillDoc.ReadLine();

            // is resulting string empty? If not, continue execution
            if (line != null)
            {
                string[] values = line.Split();
                temperature = double.Parse(values[0]);
                windSpeed = double.Parse(values[1]);

                windChillFactor = WindChillCalc(temperature, windSpeed);

                Console.WriteLine("\nFor a temperature {0:f2} F{1}", temperature, degreeSymbol);
                Console.WriteLine("and a wind velocity {0:f2}mph", windSpeed);
                Console.WriteLine("The wind chill factor = {0:f2}{1}\n", windChillFactor, degreeSymbol);
            }
        } while (line != null);

        windChillDoc.Close();

        Console.WriteLine("\nReached the end of the file, press enter to exit this program");

        Console.ReadLine();
    }//End Main()

    /// <summary>
    /// The WindChillCalc Method
    /// Evaluates a wind chill factor at a given temperature and windspeed
    /// </summary>
    /// <param name="temperature">A given temperature</param>
    /// <param name="ws">A given windspeed</param>
    /// <returns>The calculated wind chill factor, as a double</returns>
    static double WindChillCalc(double temperature, double ws)
    {
        double wci = 0.0;
        wci = FIRST_EQUATION_NUMBER + (SECOND_EQUATION_NUMBER * temperature) - (THIRD_EQUATION_NUMBER * (Math.Pow(ws, EQUATION_EXPONENT))) + (FOURTH_EQUATION_NUMBER * temperature * (Math.Pow(ws, EQUATION_EXPONENT)));
        return wci;
    }
}//End class Program 

Feel free to tell me what you think of it.

Answer 1

Your way looks good, but:

• It would look nicer if you used PascalCase for the constants, as that's what coding conventions for c# use.
• you should wrap the StreamReader in a using statement, so it gets properly disposed once you're done.
• You should probably also wrap it in a try block (and a catch to properly handle the exception) to make sure that you don't get a FileNotFound exception.
• It's probably a better idea to structure your while loop the following way:

while((line = windChillDoc.ReadLine()) != null) { ... } [Darn formatting won't work right!]

Other than that though, i wouldn't know as i'm not familiar with weather calculations :)

Answer 2

You're not going to get much zippier than that for file IO in C#. Depending on the size of the data set it may be worth using a buffered reader, but for sufficiently small files, it's just not worth it. I'd leave it as-is.

Answer 3

Most of your comments are extraneous. The code should tell you how...the comments should tell you why.

Answer 4

较小的nitpick，但是如果您使用的是英语方法名称，则“ WindChillCalc”应为“ CalcWindChill”（动词排在最前面）。

Answer 5

string filePath = "";
...
filePath = Console.ReadLine();

Don't initialize with values that are never used; and keep declaration and initialization close together:

string filePath = Console.ReadLine();

---

using has been mentioned - but don't use @ unnecessarily:

new StreamReader(@filePath);

should be just:

new StreamReader(filePath);

---

Personally, I'd use LINQ for the line-reader, but that is just me ;-p

Answer 6

Why the do/while ? In your do you check for null. In your while you check for null. Why not just make it a while statement?

string line;
while((line = windChillDoc.ReadLine()) != null)
{
    //Logic
}

EDIT : Fixed the compilation error. Funny thing was I had that originally. This Rich Text Box needs a compiler! :P

Answer 7

Although not really relating to performance (the main question)

IMO:

const double FIRST_EQUATION_NUMBER = 35.74;
const double SECOND_EQUATION_NUMBER = 0.6215;
const double THIRD_EQUATION_NUMBER = 35.75;
const double FOURTH_EQUATION_NUMBER = 0.4275;
const double EQUATION_EXPONENT = 0.16;

isn't much better than a magic number. Looking at that I have no idea what FIRST_EQUATION_NUMBER is used for other than in an equation somewhere, and I can't tell that they are in the same equation or you have four equations which use different numbers? They could also be put into the actual method as thats the only place they are used.

I would change degreeSymbol to a const rather than working it from a const int later.

const char DEGREE_SYMBOL = (char)176;

Answer 8

If you're getting marked on style etc. then there's a couple extremely minor things

• Initializing doubles to 0.0 is redundant.
• string.Empty is preferred instead of ""
• Your windchill method can be changed to simply (though, during compilation, I think that wci will be optimized out - so it's functionally the same):

(changed formatting for SO readability)

static double WindChillCalc(double temperature, double ws)
{
    return FIRST_EQUATION_NUMBER + 
        (SECOND_EQUATION_NUMBER * temperature) - 
        (THIRD_EQUATION_NUMBER * (Math.Pow(ws, EQUATION_EXPONENT))) + 
        (FOURTH_EQUATION_NUMBER * temperature * (Math.Pow(ws, EQUATION_EXPONENT)));
}

Answer 9

In little academic programs like this, unless you do something really dumb, performance will not be an issue. A simple way to tell if performance is an issue is to ask the question: "Does it make me wait?"

If there were an enormous amount of input, I would ask who's providing the input and who's reading the output. That would tell me if I could do the I/O in binary rather than text, because as it is, by far the bulk of the processing will be in the conversion of text into numbers on input, and numbers to text on output, especially floating point.