Why file operations matter in C Sharp (C#) - Challenge Your Understanding

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this file write and read code?

Consider this C# code that writes text to a file and then reads it back. What will it print?

C Sharp (C#)

using System;
using System.IO;

class Program {
    static void Main() {
        string path = "testfile.txt";
        File.WriteAllText(path, "Hello File Operations!");
        string content = File.ReadAllText(path);
        Console.WriteLine(content);
    }
}

A testfile.txt

B Hello File Operations!

C File not found exception

D Hello File Operations!\n

💡 Hint

Think about what File.WriteAllText and File.ReadAllText do.

The code writes the string "Hello File Operations!" to a file named "testfile.txt" and then reads it back. The output is exactly the string written.

🧠 Conceptual

intermediate

Why do we need to close files after opening them?

Why is it important to close a file after you finish working with it in C#?

A To convert the file to a different format

B To make the file invisible to other programs

C To delete the file automatically

D To free system resources and avoid file locks

💡 Hint

Think about what happens if many files stay open at once.

Closing files releases system resources like memory and file handles. It also allows other programs to access the file without errors.

🔧 Debug

advanced

Identify the error in this file reading code

What error will this C# code produce when run?

C Sharp (C#)

using System;
using System.IO;

class Program {
    static void Main() {
        string content = File.ReadAllText("nonexistentfile.txt");
        Console.WriteLine(content);
    }
}

A FileNotFoundException

B NullReferenceException

C ArgumentException

D No error, prints empty string

💡 Hint

What happens if you try to read a file that does not exist?

The code tries to read a file that does not exist, so the system throws a FileNotFoundException.

📝 Syntax

advanced

Which option correctly writes lines to a file?

Which of these C# code snippets correctly writes multiple lines to a file named "output.txt"?

A File.Write("output.txt", new List<string>{"Line1", "Line2"});

B File.WriteText("output.txt", "Line1\nLine2");

C File.WriteAllLines("output.txt", new string[] {"Line1", "Line2"});

D File.WriteLines("output.txt", "Line1", "Line2");

💡 Hint

Check the correct method name and parameters for writing multiple lines.

File.WriteAllLines takes a file path and a string array or IEnumerable<string> to write multiple lines. Other options use invalid method names or parameters.

🚀 Application

expert

What is the content of the file after this code runs?

Given this C# code, what will be the final content of "data.txt"?

C Sharp (C#)

using System;
using System.IO;

class Program {
    static void Main() {
        string path = "data.txt";
        File.WriteAllText(path, "Start\n");
        using (StreamWriter sw = File.AppendText(path)) {
            sw.WriteLine("Middle");
            sw.WriteLine("End");
        }
        string result = File.ReadAllText(path);
        Console.WriteLine(result);
    }
}

A Start\nMiddle\nEnd\n

B StartMiddleEnd

C Start\nMiddleEnd

D Start\nMiddle\nEnd

💡 Hint

Remember that WriteLine adds a newline after each line.

The code first writes "Start\n" to the file. Then it appends "Middle\n" and "End\n" using WriteLine. The final content has three lines, each ending with a newline.