10.3 Files: Handling Text Files with Multiple Lines

This section details how to write pseudo-code for programs that can read and process text files containing one or more lines. We will cover common operations like opening, reading, line-by-line processing, and closing files.

File Opening

Before any data can be read from a file, it must be opened. The opening process typically involves specifying the file's name and the mode in which it should be opened (e.g., 'r' for reading, 'w' for writing, 'a' for appending). In this context, we'll focus on opening a file for reading.

• The program specifies the name of the text file to be opened.
• The program requests permission to access the specified file.
• If the file exists and the program has the necessary permissions, the operating system creates a file handle (a reference to the file) and returns it to the program.
• If the file does not exist or the program lacks permissions, an error is reported.

Reading from a File Line by Line

To handle text files with multiple lines, the program needs to read the file line by line. This is typically done using a loop that iterates through the lines of the file.

1. Obtain a reference to the opened file.
2. Start a loop that continues as long as there are more lines to read in the file.
3. Inside the loop:
   • Read the next line from the file.
   • Process the line (e.g., store it in a variable, perform calculations, or print it).
4. After the loop finishes (all lines have been read), close the file.

Pseudo-code for Reading and Processing a Text File

The following is a block of pseudo-code illustrating the process of reading a text file line by line and performing a simple operation (e.g., printing each line).

Step	Action
1	Declare a variable to store the file handle (e.g., fileHandle).
2	Open the text file in read mode (e.g., fileHandle = open("filename.txt", "r")).
3	Start a loop:	While there are more lines to read in the file: Read the next line from the file into a variable (e.g., line = readLine(fileHandle)). If the line is not empty: Process the line (e.g., print(line)).
4	Close the file (e.g., close(fileHandle)).

Example Scenario

Consider a text file named "data.txt" with the following content:

This is the first line.
This is the second line.
And this is the third line.

A program using the above pseudo-code would read each of these lines and print them to the console.

Error Handling

In a real-world application, it's crucial to include error handling to deal with situations like the file not being found or errors during file operations. This might involve using try-except blocks (or equivalent constructs in the programming language) to gracefully handle such errors.