The document provides an overview of virtual functions in C++ and file handling in Perl, detailing both language features. It explains the syntax and functions for opening, reading, writing, and manipulating files in Perl, as well as Perl data types and looping constructs. Additionally, it includes examples of C++ virtual functions and various looping methods in Perl.

1. Virtual function
• // C++ program to illustrate
• // concept of Virtual Functions
• #include <iostream>
• using namespace std;
• class base {
• public:
• virtual void print() { cout << "print base classn"; }
• void show() { cout << "show base classn"; }
• };

2. • class derived : public base {
• public:
• void print() { cout << "print derived classn"; }
• void show() { cout << "show derived classn"; }
• };

3. • int main()
• {
• base* bptr;
• derived d;
• bptr = &d;
• // Virtual function, binded at runtime
• bptr->print();
• // Non-virtual function, binded at compile time
• bptr->show();
• return 0;
• }
• OUTPUT:
• PRINT derived class
• Show base clase

4. File handle in PERL

5. First program in PERL
• Perl programming language is exclusively designed for text processing
purposes. Its abbreviation denotes Practical Extraction and Report
Language. It is compatible on various platforms, such as Windows,
Mac OS, and almost all versions of UNIX.To write perl program
• Step 1: Transfer the file to Perl Interpreter:
• Always in Perl, the first line starts with a pair of characters #!. It insists
Perl interpreter how the file should be executed. Here, the file should
be transferred to Perl interpreter that resides in /usr/bin/perl folder.
• #!/usr/bin/perl

6. • Step 2: Pragma in Perl:
• A pragma is a specific module in Perl package which has the control
over some functions of the compile time or Run time behavior of Perl,
which is strict or warnings. So the next two lines go like this,
• Use strict;
• Use warnings;
• Step 3: Use of print() function:
• Print(“HELLO WROLD /n” );

7. • #!/usr/bin/perl
• # Modules used
• use strict;
• use warnings;
• # Print function
• print("Hello Worldn");
• OUTPUT:
• Hello World

8. • Important Points:
• The file must be stored with an extension of .pl
• Directory of the Perl Package must be same as to where the Program
file is saved.

9. How to Run a Perl Program?
• First, open a text editor like Notepad or Notepad++.
• Write the code in the text editor and save the file with .pl extension
• Make sure you have downloaded and installed the latest version of
Perl from https://www.perl.org/get.html
• Open commandline and Run the command perl -v to check if your
Perl’s latest version has been installed properly or not.

10. • In Perl, file handling is the process of creating, reading, writing,
updating, and deleting files. Perl provides a variety of built-in
functions and modules that make it easy to work with files.

11. File modes:
• When opening a file in Perl, you need to specify a file mode, which
determines how the file can be accessed. There are three main file
modes:
• Read mode (<): Opens the file for reading. The file must already exist.
• Write mode (>): Opens the file for writing. If the file does not exist, it
will be created. If the file already exists, its contents will be truncated.
• Append mode (>>): Opens the file for writing, but appends new data
to the end of the file instead of overwriting its contents. If the file
does not exist, it will be created.

12. File handling functions:
• open(): Opens a file and returns a file handle.
• close(): Closes a file handle.
• print(): Writes data to a file.
• read(): Reads data from a file.
• seek(): Moves the file pointer to a specific location in the file.
• tell(): Returns the current position of the file pointer.
• stat(): Returns information about a file, such as its size, owner, and
permissions.

13. • In Perl a FileHandle associates a name to an external file, that can be used until
the end of the program or until the FileHandle is closed.
• The three basic FileHandles in Perl are STDIN, STDOUT, and STDERR, which
represent Standard Input, Standard Output, and Standard Error devices
respectively. File Handling is usually done through the open function.
• Syntax: open(FileHandle, Mode, FileName);
• Parameters:
• FileHandle- The reference to the file, that can be used within the program or until
its closure.
• Mode- Mode in which a file is to be opened.
• FileName- The name of the file to be opened.

14. • Also, Mode and FileName can be clubbed to form a single expression
for opening.
• Syntax: open(FileHandle, Expression);
• Parameters:
• FileHandle- The reference to the file, that can be used within the
program or until its closure.
• Expression- Mode and FileName clubbed together.

15. • Syntax: close(FileHandle);
• Parameters:
• FileHandle- The FileHandle to be closed.

16. Different Modes in File Handling
Mode Explanation
“<“ Read Only Mode
“>”
Creates file (if necessary), Clears the contents of the File and
Writes to it
“>>” Creates file (if necessary), Appends to the File
“+<“ Reads and Writes but does NOT Create
“+>” Creates file (if necessary), Clears, Reads and Writes
“+>>” Creates file (if necessary), Reads and Appends

18. Perl data type
Perl is loosely typed language and there is no need to specify a type for
your data while using in your program. The Perl interpreter will choose
the type based on the context of the data itself.
Perl has three basic data types:
- Scalars
- arrays of scalars
- hashes of scalars, also known as associative arrays. Here is little detail
about these data types.

19. 1.Scalars: Scalars are single values. They can be strings, numbers, or references. Scalars are represented
using a dollar sign ($) . Examples include:
•Strings: $name = "John";
•Numbers: $age = 30;
•References: $array_ref = [1, 2, 3];
2.Arrays: Arrays are ordered lists of scalars. They are represented using an at sign (@) . Examples include:
•@numbers = (1, 2, 3);
•@names = ("Alice", "Bob", "Charlie");
3.Hashes: Hashes are unordered collections of key-value pairs. They are represented using a percent sign
(%) . Examples include:
•%person = ("name" => "Alice", "age" => 25);
•%grades = ("Alice" => 90, "Bob" => 85, "Charlie" => 95);
4.References: References are scalar values that refer to other data structures (scalars, arrays, hashes, or
even other references). They are represented using a backslash () sigil. Examples include:
•Reference to a scalar: $scalar_ref = $name;
•Reference to an array: $array_ref = @numbers;
•Reference to a hash: $hash_ref = %person;

20. • Examples: Consider a file Hello.txt containing the string “Welcome to PERL
PROGRAMMING” initially.
• #!/usr/bin/perl
• # Opening a File in Read-only mode
• open(r, "<", "Hello.txt");
• # Printing content of the File
• print(<r>);
• # Closing the File
• close(r);

21. Perl | Loops (for, foreach, while, do…while,
until, Nested loops)
• Looping in programming languages is a feature which facilitates the
execution of a set of instructions or functions repeatedly while some
condition evaluates to true. Loops make the programmers task
simpler. Perl provides the different types of loop to handle the
condition based situation in the program. The loops in Perl are :
• “for” loop provides a concise way of writing the loop structure. Unlike
a while loop, a for statement consumes the initialization, condition
and increment/decrement in one line thereby providing a shorter,
easy to debug structure of looping.

22. SYNTAX
For(init statement; condition; increment/decrement)
{
Code to be executed
}

23. Working

24. • init statement: This is the first statement which is executed. In this step, we
initialize a variable which controls the loop.
• condition: In this step, the given condition is evaluated and the for loop runs
if it is True. It is also an Entry Control Loop as the condition is checked prior to
the execution of the loop statements.
• Statement execution: Once the condition is evaluated to true, the statements
in the loop body are executed.
• increment/decrement: The loop control variable is changed here
(incremented or decremented) for updating the variable for next iteration.
• Loop termination: When the condition becomes false, the loop terminates
marking the end of its life cycle.

25. • #!/usr/bin/perl
• # Perl program to illustrate
• # the for loop
• # for loop
• for ($count = 1 ; $count <= 3 ; $count+=1)
• {
• print(“HELLO WORLD");
• }

26. • #!/usr/bin/perl
• @data = ('GEEKS', 'FOR', 'GEEKS');
• # foreach loop
• foreach $word (@data)
• {
• print("$wordn");
• }

27. while Loop
• A while loop generally takes an expression in parenthesis. If the
expression is True then the code within the body of while loop is
executed. A while loop is used when we don’t know the number of
times we want the loop to be executed however we know the
termination condition of the loop. It is also known as a entry
controlled loop as the condition is checked before executing the loop.
The while loop can be thought of as a repeating if statement.
Syntax :

28. Syntax :
while (condition) { # Code to be executed }

29. EXAPLE
• # Perl program to illustrate
• # the while loop
• # while loop
• $count = 3;
• while ($count >= 0)
• {
• $count = $count - 1;
• print “HELLO WORLDn";
• }

30. Infinite While Loop
• Infinite While Loop: While loop can execute infinite times which
means there is no terminating condition for this loop. In other words,
we can say there are some conditions which always remain true,
which causes while loop to execute infinite times or we can say it
never terminates.

31. • # Perl program to illustrate
• # the infinite while loop
• # infinite while loop
• # containing condition 1
• # which is always true
• while(1)
• {
• print "Infinite While Loopn";
• }

32. Output:
• INFINITE WHILE LOOP
• INFINITE WHILE LOOP
• .