Using statement with file streams in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of reading file lines with using statement

What is the output of this C# code snippet when the file test.txt contains three lines:
Line1
Line2
Line3?

C Sharp (C#)

using System;
using System.IO;

class Program {
    static void Main() {
        using (var reader = new StreamReader("test.txt")) {
            string line;
            while ((line = reader.ReadLine()) != null) {
                Console.WriteLine(line);
            }
        }
    }
}

A No output, throws exception

B Line1 Line2 Line3

C Line1\nLine2\nLine3

D Line3\nLine2\nLine1

💡 Hint

Think about how StreamReader.ReadLine() reads lines and how Console.WriteLine outputs them.

The code reads each line from the file in order and prints it on its own line. So the output matches the file lines exactly.

❓ Predict Output

intermediate

Output of writing to a file with using statement

What will be the content of output.txt after running this C# code?

C Sharp (C#)

using System;
using System.IO;

class Program {
    static void Main() {
        using (var writer = new StreamWriter("output.txt")) {
            writer.WriteLine("Hello");
            writer.WriteLine("World");
        }
    }
}

A Hello\nWorld\n

B Hello World

C HelloWorld

D File is empty

💡 Hint

Remember that WriteLine adds a new line after the text.

Each WriteLine writes the string and then a newline, so the file contains two lines: Hello and World.

❓ Predict Output

advanced

Behavior of nested using statements with file streams

What is the output of this C# program?

C Sharp (C#)

using System;
using System.IO;

class Program {
    static void Main() {
        using (var writer = new StreamWriter("nested.txt")) {
            writer.WriteLine("Start");
            using (var reader = new StreamReader("nested.txt")) {
                string content = reader.ReadToEnd();
                Console.WriteLine(string.IsNullOrEmpty(content) ? "Empty" : content);
            }
            writer.WriteLine("End");
        }
    }
}

A Throws IOException

B Start\nEnd\n

C Start

D Empty

💡 Hint

Think about when the StreamWriter flushes data to the file and when the StreamReader reads it.

The StreamWriter buffers data and does not flush before the StreamReader reads, so the file is empty at that moment.

❓ Predict Output

advanced

Output of using statement with file stream and manual flush

What will this program print?

C Sharp (C#)

using System;
using System.IO;

class Program {
    static void Main() {
        using (var writer = new StreamWriter("flush.txt")) {
            writer.WriteLine("Line1");
            writer.Flush();
            using (var reader = new StreamReader("flush.txt")) {
                Console.WriteLine(reader.ReadToEnd());
            }
        }
    }
}

A Empty

B Line1\n

C Throws IOException

D Line1

💡 Hint

Consider what Flush() does to the StreamWriter buffer.

Flush() forces the buffered data to be written to the file, so the StreamReader reads the content correctly.

🧠 Conceptual

expert

Why is using statement important with file streams?

Which of the following best explains why the using statement is important when working with file streams in C#?

A It automatically closes and disposes the file stream to free resources and avoid file locks.

B It improves the speed of file reading and writing by caching data.

C It allows multiple threads to access the file stream simultaneously without errors.

D It encrypts the file content automatically for security.

💡 Hint

Think about resource management and what happens if files are not closed properly.

The using statement ensures the file stream is closed and disposed even if exceptions occur, preventing resource leaks and file locks.