Solutions for those exercises.

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.

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?

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);
       }

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               │ 
   └────────────────┘

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.

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"
   )

7. Write a program that

   1. Asks the user to enter a path,
   2. Checks if there is a file at this path:
      1. If there is a file, display its content at the screen.
      2. If there is no file, ask the user to enter text. When the user enters exactly “!DONE!”, on a single line, without the quotes, write the text entered before !DONE! into a file located at the given path.

   Your program should be able to handle graciously possible issues (such as an invalid path).

   Below are two examples of execution, taking place one after the other.

   Example execution #1

   Enter a path  
   /͟h͟o͟m͟e͟/͟u͟s͟e͟r͟/͟C͟S͟C͟I͟_͟1͟3͟0͟2͟/͟f͟i͟n͟a͟l͟/͟t͟e͟s͟t͟.͟t͟x͟t͟
   Now creating a file at /home/user/CSCI_1302/final/test.txt.  
   Enter your text, one line at a time. When done, type "!DONE!" (without the quotes), then enter.  
   T͟h͟i͟s͟ ͟i͟s͟ ͟a͟ ͟t͟e͟s͟t͟
   s͟p͟a͟n͟n͟i͟n͟g͟ ͟o͟v͟e͟r͟
   t͟h͟r͟e͟e͟ ͟l͟i͟n͟e͟s͟.͟  
   !͟D͟O͟N͟E͟!͟
   File correctly written.

   Example execution #2

   Enter a path  
   /͟h͟o͟m͟e͟/͟u͟s͟e͟r͟/͟C͟S͟C͟I͟_͟1͟3͟0͟2͟/͟f͟i͟n͟a͟l͟/͟t͟e͟s͟t͟.͟t͟x͟t͟
   Now displaying file at /home/user/CSCI_1302/final/test.txt.  
   This is a test  
   spanning over  
   three lines.  
   Done displaying file.