C#: Read last n number of lines from a file

Last update on December 20 2024 12:49:37 (UTC/GMT +8 hours)

Write a C# Sharp program to create and read the last n lines of a file.

Sample Solution:-

C# Sharp Code:

using System; // Importing the System namespace for basic functionalities
using System.IO; // Importing the System.IO namespace for file operations

class filexercise14 // Declaring a class named filexercise14
{
    static void Main() // Declaring the Main method
    {
        string fileName = @"mytest.txt"; // Initializing a string variable with the file name
        string[] ArrLines; // Declaring an array to store lines of text
        int n, i, l, m = 1; // Declaring variables for iteration, line count, specific line to read, and iteration counter

        // Displaying a message to read the last n number of lines from a file
        Console.Write("\n\n Read last n number of lines from a file  :\n");
        Console.Write("-----------------------------------------------\n");

        if (File.Exists(fileName)) // Checking if the file exists and deleting it if true
        {
            File.Delete(fileName); // Deleting the file if it exists
        }

        Console.Write(" Input number of lines to write in the file  :");
        n = Convert.ToInt32(Console.ReadLine()); // Reading user input for the number of lines
        ArrLines = new string[n]; // Initializing the array to store lines

        Console.Write(" Input {0} strings below :\n", n); // Prompting user to input lines
        for (i = 0; i < n; i++)
        {
            Console.Write(" Input line {0} : ", i + 1);
            ArrLines[i] = Console.ReadLine(); // Reading lines of text from user input
        }

        // Writing all lines to the file
        System.IO.File.WriteAllLines(fileName, ArrLines);

        Console.Write("\n Input last how many numbers of lines you want to display  :");
        l = Convert.ToInt32(Console.ReadLine()); // Reading user input for the number of last lines to display
        m = l; // Storing l in m for iteration purposes

        if (l >= 1 && l <= n) // Checking if the specified number of lines is within the valid range
        {
            Console.Write("\n The content of the last {0} lines of the file {1} is : \n", l, fileName);
            if (File.Exists(fileName)) // Checking if the file exists
            {
                for (i = n - l; i < n; i++) // Loop to read and display last 'l' lines
                {
                    string[] lines = File.ReadAllLines(fileName); // Reading all lines from the file
                    Console.Write(" The last no {0} line is : {1} \n", m, lines[i]); // Writing specific lines to the console
                    m--; // Decrementing m for the next line number display
                }
            }
        }
        else
        {
            Console.WriteLine(" Please input the correct number of lines."); // Displaying message for incorrect line number input
        }

        Console.WriteLine();
    }
}

Sample Output:

 Read last n number of lines from a file  :                                                                   
-----------------------------------------------                                                               
 Input number of lines to write in the file  :4                                                               
 Input 4 strings below :                                                                                      
 Input line 1 : 1st line                                                                                      
 Input line 2 : 2nd line                                                                                      
 Input line 3 : 3rd line                                                                                      
 Input line 4 : 4th line                                                                                      
    
 Input last how many numbers of lines you want to display  :2                                                 
 
 The content of the last 2 lines of the file mytest.txt is :                                                  
 The last no 2 line is : 3rd line                                                                             
 The last no 1 line is : 4th line

Flowchart :

C# Sharp Code Editor:

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