File class static methods in C Sharp (C#) - Mini Project: Build & Apply

Using File Class Static Methods in C#

📖 Scenario: You are working on a simple program that manages a text file storing a list of favorite fruits. You will create the file, add some fruits, read the contents, and finally delete the file using C# File class static methods.

🎯 Goal: Build a C# program that creates a text file called fruits.txt, writes a list of fruits into it, reads and displays the fruits, and then deletes the file.

📋 What You'll Learn

Create a string array called fruits with the exact values: "Apple", "Banana", "Cherry"

Create a string variable called filePath with the exact value "fruits.txt"

Use File.WriteAllLines to write the fruits array to the file at filePath

Use File.ReadAllLines to read the contents of the file into a string array called readFruits

Use a foreach loop with variable fruit to print each fruit from readFruits

Use File.Delete to delete the file at filePath

💡 Why This Matters

🌍 Real World

Managing text files is common in many applications, such as saving user data, logs, or simple databases.

💼 Career

Knowing how to use file operations with the File class is essential for software developers working with data storage and file management.

1

Create the fruits array

Create a string array called fruits with these exact values: "Apple", "Banana", "Cherry".

C Sharp (C#)

# Your code here

Hint

Use curly braces {} to list the fruits inside the array.

2

Set the file path

Create a string variable called filePath and set it to the exact value "fruits.txt".

C Sharp (C#)

string[] fruits = { "Apple", "Banana", "Cherry" };
# Your code here

Hint

Use double quotes to set the file path string.

3

Write fruits to the file

Use File.WriteAllLines with filePath and fruits to write the fruits to the file.

C Sharp (C#)

string[] fruits = { "Apple", "Banana", "Cherry" };
string filePath = "fruits.txt";
# Your code here

Hint

Remember to include using System.IO; at the top to use the File class.

4

Read and display the fruits, then delete the file

Use File.ReadAllLines with filePath to read the file into a string array called readFruits. Then use a foreach loop with variable fruit to print each fruit. Finally, use File.Delete with filePath to delete the file.

C Sharp (C#)

using System.IO;

string[] fruits = { "Apple", "Banana", "Cherry" };
string filePath = "fruits.txt";
File.WriteAllLines(filePath, fruits);
# Your code here

Hint

Use Console.WriteLine(fruit); inside the loop to print each fruit on its own line.

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