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Files (Solutions)

Nov 16, 20246 min read

Alternative formats: pdf, odt, docx, md, source.

Questions

  1. What is the name of the class we use to read from files?

    • FileReader
    • StreamOpener
    • ReadFile
    • StreamReader
    • FileStream

  2. What is of crucial importance?

    • Always call the Open method before reading from or writing into a file.
    • Always assume the user has C:\ as their main drive.
    • Always call the Close method after being done reading from or writing into a file.
    • Never read from or write into a file inside a try…catch block.

Problems

  1. Write a program that create a text file called HelloWorld.txt in its bin/Debug folder and store “Hello” followed by a name entered by the user in it.

    Solution

     
        string uName;
    Console.WriteLine("Please, enter your name.");
    uName = Console.ReadLine();
 
    try
    {
      string filePath = Path.Combine(
        AppDomain.CurrentDomain.BaseDirectory,
        "HelloWorld.txt"
      );
      // This string contains the path for the file we create.
      StreamWriter sw = new StreamWriter(filePath);
      // We create the file
      sw.WriteLine("Hello " + uName);
      sw.Close();
      Console.WriteLine("Check out " + filePath + "!");
    }
    catch (Exception e)
    {
      Console.WriteLine("Exception: " + e.Message);
    }

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  2. Write a program that ask the user for a filename, makes sure the filename ends with “.txt” and does not begin with a ”.” (otherwise, the file would be hidden on unix systems), does not match a file with the same name in the bin/Debug folder of your program, then create it in the bin/Debug folder of your program and write in it all the number from 1 to 1,000,000 (both included). Out of curiosity, what is the file size?

    Solution

     
        string fName,
      filePath;
    do
    {
      Console.WriteLine("Enter a file name.");
      fName = Console.ReadLine();
      filePath = Path.Combine(
        AppDomain.CurrentDomain.BaseDirectory,
        fName
      );
    } while (
      !fName.EndsWith(".txt")
      || fName.StartsWith(".")
      || File.Exists(filePath)
    );
    try
    {
      StreamWriter sw = new StreamWriter(filePath);
      for (int i = 1; i <= 1000000; i++)
        sw.WriteLine(i);
      sw.Close();
      Console.WriteLine("Check out " + filePath + "!");
    }
    catch (Exception e)
    {
      Console.WriteLine("Exception: " + e.Message);
    }

    (Download this code){.download-button} The resulting file is about 6.6 MB on Unix system, 7.52 MB on Windows system.

  3. Execute the following program, then write a program that find the greatest number in the RandomNumber.txt file.

        string filePath = Path.Combine(
      AppDomain.CurrentDomain.BaseDirectory,
      "RandomNumbers.txt"
    );
    Random gen = new Random();
    try
    {
      StreamWriter sw = new StreamWriter(filePath);
      for (int i = 1; i <= 100; i++)
        sw.WriteLine(gen.Next(1000));
      sw.Close();
    }
    catch (Exception e)
    {
      Console.WriteLine("Exception: " + e.Message);
    }

    Solution

     
        string line;
    int number;
    int maxSoFar;
    try
    {
      StreamReader sr = new StreamReader(filePath);
      line = sr.ReadLine();
      if (int.TryParse(line, out number))
      {
        maxSoFar = number;
      }
      else
      {
        throw new ArgumentException(
          "File contains string that is not a number."
        );
      }
      while (line != null)
      {
        if (int.TryParse(line, out number))
        {
          if (maxSoFar < number)
          {
            maxSoFar = number;
          }
        }
        else
        {
          throw new ArgumentException(
            "File contains string that is not a number."
          );
        }
        line = sr.ReadLine();
      }
      Console.WriteLine(
        "The maximum number in the file is "
          + maxSoFar
          + "."
      );
    }
    catch (Exception e)
    {
      Console.WriteLine("Exception: " + e.Message);
    }

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  4. Suppose that at filePath is located a file where each line is either

    • a decimal (e.g., 12.4, -14, 0.34),
    • the word “STOP”,
    • some other string (“Test”, “The sky is blue”, “Ignore this line”, “My file contains”), that may contain the characters “STOP”.

    Write a program that displays the average of the decimals in the file knowing that

    • your program should ignore the values after a line containing “STOP” and only “STOP” if it is present,
    • all the other strings should simply be ignored.

    For example, for the following three files, “4.0”, “10.0” and “7.5” should be displayed, as (12.48 - 2.48 + 2) / 3 = 4 (13 been ignored), (15 + 5) / 2 = 10, and (11 + 4) / 2 = 7.5 (12 being ignored).

    ┌────────────────┐
│12.48           │
│This is a test  │     
│-2.48           │
│2               │
│STOP            │
│13              │
└────────────────┘
 
┌────────────────┐
│My file contains│
│STOP but        │
│averages        │
│15              │
│     and        │
│5               │ 
└────────────────┘
 
┌────────────────┐
│This 12 will be │
│ignored         │
│but not         │
│11              │
│     nor        │
│4               │ 
└────────────────┘

    Solution

     
          double number;
      double sum = 0;
      int counter = 0;
      double average;
      try
      {
        // Opening file
        StreamReader sr = new StreamReader(filePathP);
        // Reading first line
        string line = sr.ReadLine();
 
        // Looping through the file until we
        // reach the end, or read the word
        // "STOP" on its own line.
        while (line != null && line != "STOP")
        {
          // We test if the line contains a double.
          if (double.TryParse(line, out number))
          {
            sum += number;
            counter++;
          }
          // We read the next line.
          line = sr.ReadLine();
        }
        sr.Close();
      }
      catch { }
      // if to prevent division by 0.
      if (counter != 0)
      {
        average = sum / counter;
      }
      else
      {
        average = -1;
      }

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  5. Write a program that asks the user to enter a sentence, and store it in a file where the maximum width is 40: if the string entered is more than 40 characters long, then it should span over multiple lines of no more than 40 characters each. For example, if the user enters

    In publishing and graphic design, Lorem ipsum is a placeholder text commonly used to demonstrate the visual form of a document or a typeface without relying on meaningful content. Lorem ipsum may be used as a placeholder before the final copy is available.

    then the text file should contain

    In publishing and graphic design, Lorem 
ipsum is a placeholder text commonly use
d to demonstrate the visual form of a do
cument or a typeface without relying on 
meaningful content. Lorem ipsum may be u
sed as a placeholder before the final co
py is available.

    Solution

     
        string filePath = Path.Combine(
      AppDomain.CurrentDomain.BaseDirectory,
      "TextTruncate.txt"
    );
    Console.WriteLine("Enter a string.");
    string uString = Console.ReadLine();
 
    const int MAXWIDTH = 40;
 
    try
    {
      StreamWriter sw = new StreamWriter(filePath);
      while (uString.Length > MAXWIDTH)
      {
        sw.WriteLine(uString.Substring(0, MAXWIDTH));
        uString = uString.Substring(MAXWIDTH);
      }
      sw.WriteLine(uString);
      sw.Close();
    }
    catch (Exception e)
    {
      Console.WriteLine("Exception: " + e.Message);
    }

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  6. Write a program that counts the number of words in itself! Ideally, empty lines should not count toward the word count.

    Hint: Program.cs is normally located at

    Path.Combine(
    new DirectoryInfo(Directory.GetCurrentDirectory()).Parent.Parent.ToString(),
    "Program.cs"
)

    Solution

     
    using System;
using System.IO;
 
class Program
{
  static void Main()
  {
    // The following goes to /bin/Debug, then two folders up,
    // where Program.cs is located.
    string filePath = Path.Combine(
      new DirectoryInfo(
        Directory.GetCurrentDirectory()
      ).Parent.Parent.ToString(),
      "Program.cs"
    );
 
    if (!File.Exists(filePath))
    {
      Console.WriteLine(
        "There seems to be an issue. Impossible to locate Program.cs"
      );
    }
    else
    {
      Console.WriteLine("Program.cs located, processing.");
      string line;
      string[] words;
      int wCount = 0;
      try
      {
        StreamReader sr = new StreamReader(filePath);
        line = sr.ReadLine();
        while (line != null)
        {
          words = line.Split(
            new string[] { " " },
            StringSplitOptions.RemoveEmptyEntries
          );
          wCount += words.Length;
          line = sr.ReadLine();
        }
        sr.Close();
        Console.WriteLine(
          "Your program contains " + wCount + " words!"
        );
        // Should display "Your program contains 121 words!"
      }
      catch (Exception e)
      {
        Console.WriteLine("Exception: " + e.Message);
      }
    }
  }
}

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