File class static methods in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if a file exists at the given path.

C Sharp (C#)

bool exists = File.[1]("example.txt");

Drag options to blanks, or click blank then click option'

AReadAllText

BExists

CDelete

DCopy

Attempts:

3 left

💡 Hint

Common Mistakes

Using ReadAllText instead of Exists causes runtime error if file missing.

Using Delete or Copy does not check existence.

The File.Exists method checks if the specified file exists and returns a boolean.

2fill in blank

medium

Complete the code to read all text from a file into a string.

C Sharp (C#)

string content = File.[1]("data.txt");

Drag options to blanks, or click blank then click option'

AReadAllText

BWriteAllText

CAppendAllText

DDelete

Attempts:

3 left

💡 Hint

Common Mistakes

Using WriteAllText tries to write, not read.

AppendAllText adds text instead of reading.

File.ReadAllText reads the entire content of a text file into a string.

3fill in blank

hard

Fix the error in the code to copy a file from source to destination.

C Sharp (C#)

File.[1]("source.txt", "dest.txt");

Drag options to blanks, or click blank then click option'

ADelete

BMove

CCopy

DExists

Attempts:

3 left

💡 Hint

Common Mistakes

Using Delete removes the file instead of copying.

Using Move moves the file instead of copying.

File.Copy copies a file from one path to another.

4fill in blank

hard

Fill both blanks to write text to a file, overwriting if it exists.

C Sharp (C#)

File.[1]("log.txt", [2]);

Drag options to blanks, or click blank then click option'

AWriteAllText

B"Hello, world!"

C"Sample text"

DAppendAllText

Attempts:

3 left

💡 Hint

Common Mistakes

Using AppendAllText adds text instead of overwriting.

Passing a variable name instead of a string literal.

File.WriteAllText writes the given string to the file, replacing existing content.

5fill in blank

hard

Fill all three blanks to move a file only if it exists.

C Sharp (C#)

if (File.[1]("old.txt")) {
    File.[2]("old.txt", [3]);
}

Drag options to blanks, or click blank then click option'

AExists

BMove

C"new.txt"

DCopy

Attempts:

3 left

💡 Hint

Common Mistakes

Using Copy instead of Move changes file behavior.

Not checking if file exists before moving.

First, File.Exists checks if the file is there. Then File.Move moves it to the new path "new.txt".

Practice

1. Which of the following File class static methods checks if a file exists at a given path?

easy

A. File.Exists(path)

B. File.ReadAllText(path)

C. File.Delete(path)

D. File.Copy(source, destination)

Solution

1. Step 1: Understand the purpose of each method

   File.Exists(path) checks if the file is present. File.ReadAllText(path) reads file content. File.Delete(path) deletes a file. File.Copy(source, destination) copies a file.

2. Step 2: Identify the method that checks existence

   The method that returns a boolean indicating if the file exists is File.Exists(path).

3. Final Answer:

   File.Exists(path) -> Option A

4. Quick Check:

   Check file existence = File.Exists(path) [OK]

Hint: Exists method returns true if file is present [OK]

Common Mistakes:

• Confusing ReadAllText with Exists
• Using Delete to check existence
• Thinking Copy checks file presence

2. Which of the following is the correct syntax to write text to a file using the File class?

easy

A. File.WriteText(path, "Hello World");

B. File.WriteAllText(path, "Hello World");

C. File.Write(path, "Hello World");

D. File.WriteLine(path, "Hello World");

Solution

1. Step 1: Recall the correct method name for writing text

   The File class uses WriteAllText to write all text to a file at once.

2. Step 2: Check method signatures

   WriteText, Write, and WriteLine are not valid static methods of File class.

3. Final Answer:

   File.WriteAllText(path, "Hello World") -> Option B

4. Quick Check:

   Write text to file = WriteAllText [OK]

Hint: Use WriteAllText to write full text at once [OK]

Common Mistakes:

• Using non-existent WriteText method
• Confusing File class with StreamWriter methods
• Using WriteLine which is not in File class

3. What will be the output of the following code if the file "test.txt" contains the text "Hello"?

string content = File.ReadAllText("test.txt");
Console.WriteLine(content);

medium

A. Hello

B. test.txt

C. File.ReadAllText

D. Error: File not found

Solution

1. Step 1: Understand what File.ReadAllText does

   This method reads all text from the specified file and returns it as a string.

2. Step 2: Analyze the code output

   The variable content will hold "Hello" from the file. The Console.WriteLine prints this string.

3. Final Answer:

   Hello -> Option A

4. Quick Check:

   ReadAllText returns file content [OK]

Hint: ReadAllText returns file content as string [OK]

Common Mistakes:

• Printing file name instead of content
• Expecting method name as output
• Assuming error without checking file existence

4. Identify the error in the following code snippet:

File.Copy("source.txt", "dest.txt");
File.Delete("source.txt");
File.Copy("source.txt", "dest.txt");

medium

A. No error, code runs fine

B. File.Delete should be called before the first File.Copy

C. File.Copy cannot copy files with .txt extension

D. Second File.Copy will throw an exception because source.txt was deleted

Solution

1. Step 1: Trace the file operations

   First, source.txt is copied to dest.txt. Then source.txt is deleted. Finally, the code tries to copy source.txt again.

2. Step 2: Identify the problem

   After deletion, source.txt no longer exists, so the second copy call will throw a FileNotFoundException.

3. Final Answer:

   Second File.Copy will throw an exception because source.txt was deleted -> Option D

4. Quick Check:

   Copy after delete causes error [OK]

Hint: Cannot copy a file after deleting it [OK]

Common Mistakes:

• Assuming File.Copy works on deleted files
• Thinking order of Delete and Copy doesn't matter
• Believing .txt files cannot be copied

5. You want to create a backup of a file only if it exists, without overwriting an existing backup. Which code snippet correctly uses File class static methods to do this?

hard

A. if (File.Exists("file.txt")) File.Copy("file.txt", "backup.txt", true);

B. File.Copy("file.txt", "backup.txt");

C. if (File.Exists("file.txt") && !File.Exists("backup.txt")) File.Copy("file.txt", "backup.txt");

D. File.Copy("file.txt", "backup.txt", false);

Solution

1. Step 1: Understand the requirements

   Backup only if original file exists and do not overwrite existing backup file.

2. Step 2: Analyze each option

   if (File.Exists("file.txt")) File.Copy("file.txt", "backup.txt", true); overwrites backup.txt because of 'true' overwrite flag. if (File.Exists("file.txt") && !File.Exists("backup.txt")) File.Copy("file.txt", "backup.txt"); checks existence of both files and copies only if backup.txt does not exist. File.Copy("file.txt", "backup.txt"); copies without checks, risking errors or overwrites. File.Copy("file.txt", "backup.txt", false); copies without overwrite but does not check if original file exists.

3. Final Answer:

   if (File.Exists("file.txt") && !File.Exists("backup.txt")) File.Copy("file.txt", "backup.txt"); -> Option C

4. Quick Check:

   Check both files before copy to avoid overwrite [OK]

Hint: Check both files exist before copying without overwrite [OK]

Common Mistakes:

• Not checking if backup file exists
• Using overwrite flag incorrectly
• Copying without checking original file existence