Welcome to the first lesson in our course on "Fundamentals of Text Data Manipulation." This lesson will introduce you to the essential task of reading text files in C#. Text files are a fundamental data source in programming, commonly used for storing data, configuration files, and logs. Being able to open and read files in C# is a foundational skill you'll often rely on when working with data. By the end of this lesson, you will be able to read the entire contents of a text file into a string using C#'s File.ReadAllText method, a crucial capability for various data manipulation tasks. Let's get started!

A file path is an address that indicates where a file is located in your system's storage. This path guides your program on where to find or save a file. There are two types of file paths commonly used:

• Absolute Path: This is the complete path to a file, starting from the root directory. Here are examples across different operating systems:

  • Linux: /home/user/documents/input.txt
  • macOS: /Users/user/documents/input.txt
  • Windows: C:\\Users\\user\\documents\\input.txt (note the double backslashes for escaping)

• Relative Path: This path is relative to the directory in which your application is currently executing. For example, documents/input.txt assumes your executable is running from the user directory in these examples.

Here's how you can specify a file path in C#:

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1string filePath = "input.txt";  // Relative path

Make sure your C# program and the text file are in the same directory if you use a relative path. Otherwise, consider using the absolute path to ensure that your program can locate your file.

When working with relative paths in C#, it's important to understand your directory's structure. Here are a few examples with file trees:

1. Example 1:

   File Tree:

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   1project/
   2├── program
   3└── data/
   4    └── input.txt

   Relative Path:

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   1string filePath = "data/input.txt";

2. Example 2:

   File Tree:

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   1user/
   2├── documents/
   3│   └── program
   4└── input.txt

   Relative Path:

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   1string filePath = "../input.txt";

   The .. indicates moving up to the parent directory. This approach works similarly across platforms like macOS/Linux and Windows.

3. Example 3:

   File Tree:

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   1application/
   2├── scripts/
   3│   ├── program1
   4│   └── program2
   5└── resources/
   6    └── input.txt

   Relative Path (assuming the program is in program2):

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   1string filePath = "../resources/input.txt";

These examples demonstrate how relative paths are determined by the program's current working directory.

In C#, the File class from System.IO provides methods to handle file input. To open and read a file, you use the ReadAllText method. Here is how you can use it:

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1string filePath = "example.txt";
2string content = File.ReadAllText(filePath);

In this snippet, ReadAllText reads the entire content of the specified file into a string variable, content.

To display the contents of a file in C#, now that we have already read the file's contents into a string variable using the File.ReadAllText method, you can simply print the string to the console:

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1Console.WriteLine("Full file content:");
2Console.WriteLine(content);

In this snippet, the content variable, which contains the entire file's contents, is printed using Console.WriteLine, allowing you to view all the data stored in the file.

In this lesson, you've learned how to:

• Correctly specify file paths with examples from different operating systems using C#.
• Utilize C#'s File class to open a file and manage the data through the ReadAllText method.
• Read the entire contents of a file from disk into a string variable.

These fundamental skills are crucial for handling data stored in text files. As you proceed to the practice exercises, you will apply these concepts by reading and extracting content from different text files. This hands-on practice will reinforce your understanding and prepare you for more advanced file manipulation techniques in the future. Keep up the great work, and happy coding!