StreamReader and StreamWriter in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Reading lines with StreamReader

What is the output of this C# code snippet?

C Sharp (C#)

using System;
using System.IO;

class Program {
    static void Main() {
        string text = "Hello\nWorld";
        using (var reader = new StringReader(text)) {
            string line1 = reader.ReadLine();
            string line2 = reader.ReadLine();
            Console.WriteLine(line1);
            Console.WriteLine(line2);
        }
    }
}

A Hello\nWorld

B Hello\nWorld\nHello

C Hello\nWorld\n

D Hello\nWorld\nnull

💡 Hint

ReadLine reads one line at a time, stopping at newline characters.

The ReadLine method reads one line at a time. The first call reads "Hello", the second reads "World". Console.WriteLine adds a newline after each, so the output is Hello\nWorld\n.

❓ Predict Output

intermediate

Writing and reading text with StreamWriter and StreamReader

What will be printed by this C# program?

C Sharp (C#)

using System;
using System.IO;

class Program {
    static void Main() {
        string path = "test.txt";
        using (var writer = new StreamWriter(path)) {
            writer.WriteLine("Line1");
            writer.WriteLine("Line2");
        }
        using (var reader = new StreamReader(path)) {
            string content = reader.ReadToEnd();
            Console.Write(content);
        }
        File.Delete(path);
    }
}

A Line1\nLine2\n

B Line1Line2

C Line1\nLine2

D Line1\nLine2\nnull

💡 Hint

WriteLine adds a newline after each line.

StreamWriter.WriteLine writes the string and adds a newline. ReadToEnd reads the whole file including newlines. So output includes both lines separated by newlines.

❓ Predict Output

advanced

StreamReader Read vs ReadLine behavior

What is the output of this C# code?

C Sharp (C#)

using System;
using System.IO;

class Program {
    static void Main() {
        string text = "abc\ndef";
        using (var reader = new StringReader(text)) {
            int firstChar = reader.Read();
            string line = reader.ReadLine();
            Console.WriteLine((char)firstChar);
            Console.WriteLine(line);
        }
    }
}

A a\nbc

B a\ndef

C a\ncdef

D a\nb

💡 Hint

Read reads one character, ReadLine reads until newline or end.

Read reads 'a' (first char). Then ReadLine reads the rest of the first line after 'a', which is 'bc'. The newline is consumed by ReadLine but not included in output.

❓ Predict Output

advanced

StreamWriter AutoFlush effect

What will this program print?

C Sharp (C#)

using System;
using System.IO;
using System.Text;

class Program {
    static void Main() {
        using (var ms = new MemoryStream()) {
            using (var writer = new StreamWriter(ms)) {
                writer.AutoFlush = false;
                writer.Write("Hello");
                Console.WriteLine(Encoding.UTF8.GetString(ms.ToArray()));
                writer.Flush();
                Console.WriteLine(Encoding.UTF8.GetString(ms.ToArray()));
            }
        }
    }
}

A Hello\nHello

B olleHn\olleH

C \n\nHello

D \nHello

💡 Hint

AutoFlush controls when data is sent to the underlying buffer.

With AutoFlush false, Write does not immediately update the underlying stream, so first print is empty. After Flush(), the stream contains "Hello".

🧠 Conceptual

expert

StreamReader disposal and file locking

Which option correctly describes what happens if you forget to dispose a StreamReader after reading a file?

A The file is immediately unlocked and can be accessed by other processes even if StreamReader is not disposed.

B The file remains locked and cannot be accessed by other processes until the program ends or garbage collection runs.

C The StreamReader automatically disposes itself after reading the file, so no locking occurs.

D The file is deleted automatically when StreamReader is not disposed.

💡 Hint

Think about resource management and file locks in Windows.

If StreamReader is not disposed, the underlying file handle remains open, locking the file. Other processes cannot access it until disposal or program exit.