DEV Community: Sasireka

Pincode, Phone number, and Gmail Validation Programs in Python

Sasireka — Mon, 20 Apr 2026 08:38:52 +0000

1) Pincode Validation

regions = {
    1: "Delhi",
    2: "Uttar Pradesh & Uttarakhand",
    3: "Rajasthan & Gujarat",
    4: "Maharashtra",
    5: "Andhra Pradesh & Telangana",
    6: "Tamil Nadu & Kerala",
    7: "West Bengal & North East",
    8: "Bihar & Jharkhand",
    9: "Army Postal Service"
}

sub_regions = {
    11: "Delhi Region",
    40: "Mumbai Region",
    60: "Chennai Region",
    70: "Kolkata Region"
}

districts = {
    110: "Delhi",       111: "Delhi (North)",      112: "Delhi (South)",
    400: "Mumbai",      401: "Mumbai (Suburban)",   402: "Mumbai (West)",
    600: "Chennai",     601: "Tiruvallur",          602: "Kanchipuram",
    700: "Kolkata",     701: "Kolkata (North)",     702: "Kolkata (South)"
}

def get_pincode_details(pincode):
    if not pincode.isdigit() or len(pincode) != 6:
        print("Invalid pincode. Enter exactly 6 digits.")
        return

    num         = int(pincode)
    first_digit = num // 100000
    first_two   = num // 10000
    first_three = num // 1000

    print("Region:     ", regions.get(first_digit,   "Unknown"))
    print("Sub-region: ", sub_regions.get(first_two, "Unknown"))
    print("District:   ", districts.get(first_three, "Unknown"))

pincode = input("Enter Pincode: ").strip()
get_pincode_details(pincode)

Output:

2) Phone Number Validation

def verify(mobnum):
    index=0
    while index<len(mobnum):
        if mobnum[index]>="0" and mobnum[index]<="9":
            index+=1
            continue;
        else:
            return False
    return True



def mobile(n):
    i=0
    while i<len(n):
        if(n[i]>="0" and n[i]<="9") or (n[i]=="+") or (n[i]==" "):
            i+=1
        else:
            return "characters and special charactors not allowed"

    if len(n)==10:
        if n[0]>="6" and n[0]<="9" and verify(n):
            return "valid";
        else:
            return "incorrect"

    if len(n)==13:
        if n[0:3]=="+91":
            if n[3]>="6" and n[3]<="9" and verify(n[3:]):
                return "valid"
            else:
                return "incorrect"
        return "First three number should like +91"

    if len(n)==14:
        if n[0:4]=="+91 ":
            if n[4]>="6" and n[4]<="9" and verify(n[4:]):
                return "valid"
            else:
                return "incorrect"
        return "First four number should like +91 "
    return "Please Enter Your valid Mobile Number"      
print(mobile(input("Enter Your Mobile  Number : ")));

Output:

3) Gmail Validation

def verify_Gmail(Gmail):
    if Gmail[-10:]=="@gmail.com":
        i=0
        gmailcopy=Gmail[0:len(Gmail)-10]
        while i<len(gmailcopy):
            current=gmailcopy[i]
            i+=1
            if current>="a" and current<="z":
                continue;
            elif current>="A" and current<="Z":
                continue;
            elif current>="0" and current<="9":
                continue;
            elif current=="." or current=="_":
                continue;
            else:
                return False
        return True
    else:
        return False

if verify_Gmail(input("Enter Your Gmail :")):
    print("valid")
else:
    print("invalid")

Output:

Constructor in Java

Sasireka — Fri, 17 Apr 2026 16:49:31 +0000

1) What is Constructor?

A constructor is a special method in Java used to initialize objects. It is automatically called when an object of a class is created.

Name: A constructor must have the same name as the class.
No Return Type: A constructor does not have a return type, not even void.

2) Types of Constructor

Default Constructor:

A default constructor is a constructor with no parameters.

The Java compiler makes a default constructor if we do not write any constructor in our program.

Example:

public class Student{

    String name;
    int age;

    // Default Constructor
    public Student(){

        System.out.println("Default constructor"); 

    }
    public static void main(String[] args){

        Student student1 = new Student();
        student1.name = "Sasireka";
        student1.age = 23;
        System.out.println(student1.name);
        System.out.println(student1.age);
    }
}

Output:

Parameterized Constructor:

A parameterized constructor is used to assign values to object variables when the object is created.

Example:

public class Student {
  String name;
  int age;

  //Parameterized constructor
  public Student(String Name, int Age){
      name = Name;
      age = Age;
  }

  public static void main(String args[]) {
    Student student1 = new Student("Sasireka", 23);
    System.out.println(student1.name);
    System.out.println(student1.age);
  }

}

Output:

3) Constructor Overloading

Constructor overloading - A class have more than one constructor with different no of parameters or with different type of parameter.

Example:

public class Student {
  String name;
  int age;

  //constructor overloading
  public Student(String Name, int Age){
      name = Name;
      age = Age;
  }

  public Student(){
      System.out.println("Constructor");
  }

  public static void main(String args[]) {
    Student student1 = new Student("Sasireka", 23);
    System.out.println(student1.name);
    System.out.println(student1.age);

    Student myStudent1 = new Student();

  }

}

Output:

Test Cases

Sasireka — Wed, 15 Apr 2026 17:26:22 +0000

1) What is Test Case?

A test case is a set of conditions or steps used to check whether a software feature works correctly or not.

2) Main Components of a Test Case

Test Case no – Unique number
Test Scenario – What we are testing
Test Steps – Actions to perform
Expected Result – What should happen
Actual Result – What actually happened
Attachment - Screenshot

3) Why Test Cases are Important?

Ensure the application works correctly
Help find bugs/errors
Improve software quality
Useful for documentation and re-testing

Example: Sign Up Page

Waterfall and V models

Sasireka — Mon, 13 Apr 2026 04:51:20 +0000

1) What is Waterfall model?

The Waterfall Model is a traditional software development methodology that follows a linear, phase-by-phase approach, where each phase must be completed before moving to the next.

It does not allow backtracking and permits only minimal changes once a phase is completed.

Waterfall Model:

Phases of Waterfall Model

Requirement Analysis

All project requirements are gathered and documented at the beginning.

System Design

The system architecture and design are created based on requirements.

Development

Developers write code according to the design.

Testing

The completed system is tested to identify bugs and errors.

Deployment

The software is delivered to the client or released to users.

Maintenance

Fixing bugs and updating the system after deployment.

Advantages

Easy to manage due to structured phases
Works well for small projects
Clear requirements reduce confusion
Good for projects with fixed scope

Disadvantages

Not flexible (changes are difficult once the process starts)
Late testing may lead to higher risk
Not suitable for complex or long-term projects
Customer feedback is limited during development

When to Use

When requirements are clear and fixed
Small or simple projects
Projects with strict deadlines and budgets

2) What is V Model?

The V-Model is an extension of the Waterfall Model. It emphasizes testing at every stage of development, making it more structured and quality-focused.

The name “V-Model” comes from its shape, where the left side represents development phases and the right side represents testing phases.

V Model (Verification and Validation Model):

Verification → Are we building the product right?
Validation → Are we building the right product?

Structure of V-Model

Left Side (Development Phases)

Requirement Analysis
System Design
High-Level Design
Low-Level Design

Right Side (Testing Phases)

Unit Testing
Integration Testing
System Testing
Acceptance Testing

Each development phase has a corresponding testing phase.

Advantages

Early detection of defects
Strong focus on testing
Better quality product
Easy to manage and track progress

Disadvantages

Less flexible like Waterfall
Changes are hard to implement
Not suitable for dynamic or evolving requirements
Can be costly for large projects

When to Use

Projects with clearly defined requirements
Safety-critical systems (like healthcare, banking)
When high quality and testing are required

IP Address Range

Sasireka — Sat, 11 Apr 2026 17:30:30 +0000

1) What is IP Address?

An IP Address (Internet Protocol Address) is a unique number assigned to every device connected to a network. It helps devices communicate with each other over the internet.

Just like a home address helps in delivering parcels, an IP address helps in sending and receiving data between devices.

2) Why do we need it?

IP addresses are essential because they:

Identify devices on a network
Enable communication between devices
Help in sending and receiving data accurately

Without an IP address, the internet cannot function properly.

3) Types of IP Address

IPv4

The most commonly used type of IP address.

Format: 192.168.1.1
It consists of 4 numbers separated by dots

IPv6

The newer version designed to replace IPv4.

Format: 2001:0db8:85a3::7334
Uses hexadecimal numbers (0–9 and A–F)
Provides a much larger number of addresses

4) IPv4 Address Range

0.0.0.0 → 255.255.255.255

This means:

Minimum IP address: 0.0.0.0
Maximum IP address: 255.255.255.255
Total Number of IPv4 Addresses: 2³² = 4,294,967,296

Private IP Address Ranges

Private IP addresses are used within local networks such as homes, offices, and organizations.

10.0.0.0 → 10.255.255.255
172.16.0.0 → 172.31.255.255
192.168.0.0 → 192.168.255.255

These IPs are not accessible directly over the internet and are mainly used for internal communication.

Loopback Address

127.0.0.1 - Known as localhost
Used to test networking on the same device

Special IP Addresses

0.0.0.0 → Represents an unknown or default network
255.255.255.255 → Used as a broadcast address to communicate with all devices in a network

5) IPv6 Address Range

0000:0000:0000:0000:0000:0000:0000:0000
to
FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF

Total IPv6 Addresses - 2¹²⁸ (extremely large number)
This is approximately 340 undecillion addresses, ensuring we never run out of IPs.

Each Block Range

Each of the 8 blocks in IPv6 can range from: 0000 to FFFF
Each block has 65,536 possible values.

Why IPv6 is Huge?

IPv4 → 32 bits → ~4 billion addresses
IPv6 → 128 bits → extremely large number of addresses

Self-Introduction

Sasireka — Thu, 09 Apr 2026 16:20:13 +0000

Myself Sasireka A, I have completed my Master's in Computer Science from PSGR Krishnammal College for Women. I'm Currently pursuing a Full Stack Java Course at Payilagam in Chennai.

I have Knowledge in Web technologies such as HTML, CSS, Javascript, and React. During my academic project, I developed a Healthcare portal where patients can easily book appointments with doctors through online.

In this project, I used HTML and CSS for designing the user interface, Javascript for functionality and React.js for building reusable components and improve performance.

As a fresher, I bring a positive attitude, a strong willingnes to learn, and the ability to adapt quickly to new technologies and work environment.

I am looking forward to starting my career in a company where I can learn and contribute to real-world projects.

Constructor in Javascript

Sasireka — Thu, 09 Apr 2026 08:47:58 +0000

What is a Constructor in JavaScript?

A constructor is a special function that creates and initializes an object instance of a class. In JavaScript, a constructor gets called when an object is created using the new keyword.
The purpose of a constructor is to create a new object and set values for any existing object properties.

JavaScript Constructor Examples

Here’s a few examples of constructors in JavaScript:

Using the "this" Keyword

When the this keyword is used in a constructor, it refers to the newly created object:

function User() {
    this.name = 'Sasi';
}

var user = new User();
console.log(user)

Create Multiple Objects

In JavaScript, multiple objects can be created in a constructor:

function User() {
this.name = 'Sasi';
}

var user1 = new User();
var user2 = new User();
console.log(user1)
console.log(user2)

Constructor with Parameters

A constructor can also have parameters:

function User (name, age) {
    this.name = name;
    this.age = age;
}

var user1 = new User('Sasi', 23);
var user2 = new User('Keerthi', 24);
console.log(user1)
console.log(user2)

ASCII Values of Each Character in JavaScript

Sasireka — Wed, 08 Apr 2026 15:34:57 +0000

What is ASCII?

ASCII (American Standard Code for Information Interchange) is a, standard code that assigns numerical values (0–127) to letters, numbers, and symbols, allowing computers to understand text.

It was the standard for character representation in computers and data communication from the 1960s, heavily influencing modern systems.

It primarily supports English; however, it serves as the base for Unicode (the first 128 Unicode characters are identical to ASCII).

Non-Printable Characters (0-31)

Example: 0 => Null , 8 => Backspace , 9 => Tab , 10 => New Line

Printable Characters (32-126)

Example: [65-90 => A-Z] , [97-122 => a-z] , [48-57 => 0-9(Numbers)]

Del Character (127)

Delete (Non-Printable)

Example Program:

let name = "silambu9391a@gmail.com";

for (let i = 0; i < name.length; i++) {
    console.log(name[i] + " = " + name.charCodeAt(i));
}

Explanation:

i = 0 → starts from first character
name.length → total number of characters
i++ → moves to next character
Gets character at position i

Example:
name[0] → 's'
name[1] → 'i'
name[2] → 'l'

name.charCodeAt(i)
Converts character → ASCII number

Example:
's' → 115
'i' → 105
'l' → 108
'a' → 97

Prints: character = ASCII value

Output:

Method Overloading in Java

Sasireka — Wed, 08 Apr 2026 08:04:59 +0000

1) What is Method?

In Java, a method is a block of code that performs a specific task and only runs when it is called.
Methods are used to define the behavior of objects and classes, allowing you to reuse code without retyping it.
Java categorizes methods into two primary types:

Predefined (Standard Library) Methods: Built-in methods provided by Java libraries, such as System.out.println() or Math.sqrt().

User-defined Methods: Custom blocks of code written by programmers to solve specific problems.

2) What is Method Overloading?

Method overloading in Java is a feature that allows a class to have multiple methods with the same name, provided they have different parameter lists.
It is a form of compile-time polymorphism (also known as static binding), where the Java compiler determines which method to call based on the arguments provided.

3) Core Rules for Overloading

To successfully overload a method, the method signature (name + parameters) must be unique. Methods can be overloaded by changing:

Number of Parameters: For example, add(int a, int b) and add(int a, int b, int c).
Data Types of Parameters: For example, display(int a) and display(String a).
Order of Parameters: For example, process(int a, String b) and process(String b, int a).

Example:

public class Calc {

    public static void main(String[] args) {
        Calc obj = new Calc();

        System.out.println(obj.add(10, 20));        // Method 1
        System.out.println(obj.add(10, 20, 30));    // Method 2
        System.out.println(obj.add(10.5, 20.5));    // Method 3
    }

    // Method 1: Two integers
    public int add(int a, int b) {
        return a + b;
    }

    // Method 2: Three integers
    public int add(int a, int b, int c) {
        return a + b + c;
    }

    // Method 3: Double values
    public double add(double a, double b) {
        return a + b;
    }
}

Output:

Methods in Java

Sasireka — Wed, 08 Apr 2026 07:49:32 +0000

1) Void Method (No Return Value)

public class Home{
    public static void main(String[] args){
        Home obj = new Home();
        obj.display();
    }
    public void display(){
        return;
    }
}

Explanation:

display() method has void return type
return; is used just to exit the method
Since there is no print statement, nothing is displayed.

Output: Nothing is displayed

2) Marks Calculation Program

public class Marks{
    public static void main(String[] args){
        Marks obj = new Marks();
        int total = obj.SumMarks(70,80,67,54,91);
        int average = obj.AvgMarks(total,5);
        obj.Grade(average);
    }
    public int SumMarks(int no1,int no2,int no3,int no4,int no5){
        return no1+no2+no3+no4+no5;
    }
    public int AvgMarks(int no1,int no2){
        return no1/no2;
    }
    public void Grade(int no1){
        if(no1>90){
            System.out.println("A Grade");
        }
        else if(no1>80){
            System.out.println("B Grade");
        }
        else if(no1>70){
            System.out.println("C Grade");
        }
        else{
            System.out.println("D Grade");
        }
    }
}

Explanation:

SumMarks() → returns total marks
AvgMarks() → returns average
Grade() → void return type (no value returned)
Grade() method uses if-else to decide grade
System.out.println() is used → to display output

Output:

String Manipulation in Python

Sasireka — Wed, 08 Apr 2026 05:39:53 +0000

What is String?

A String is a sequence of characters (letters, numbers, symbols) written together as text.

1) Accessing Characters in a String

name = "Sasi"

print(name[0])  # First character
print(name[1])  # Second character
print(name[-1])  # Last character
print(name[-2])  # Second last

Output:

2) Convert String to Uppercase

name = "sasi"

result = name.upper()
print(result)

Output:

3) Convert String to Lowercase

name = "SASI"

result = name.lower()
print(result)

Output

4) Convert First and Last Character to Uppercase

name = "sasi"

result = name[0].upper() + name[1:-1] + name[-1].upper()
print(result)

Output:

5) Convert Middle Character to Uppercase

name = "sasireka"

mid = len(name) // 2   # find middle index

result = name[:mid] + name[mid].upper() + name[mid+1:]

print(result)

Explanation:

len(name) = 8
mid = 8 // 2 = 4
Middle character → name[4] = 'r'
Convert 'r' → 'R'
name[:mid] → "sasi"
name[mid].upper() → "R"
name[mid+1:] → "eka"

Output:

6) Convert First, Middle and Last Character to Uppercase

name = "sasireka"

mid = len(name) // 2   

result = (name[0].upper() +  name[1:mid] +  name[mid].upper() +  name[mid+1:-1] +  name[-1].upper())

print(result)

Explanation:

len(name) = 8
mid = 8 // 2 = 4
First character → name[0] = 's'
Middle character → name[4] = 'r'
Last character → name[7] = 'a'
Convert:

's' → 'S'
'r' → 'R'
'a' → 'A'
name[0].upper() → "S"
name[1:mid] → "asi"
name[mid].upper() → "R"
name[mid+1:-1] → "ek"
name[-1].upper() → "A"

Output:

Return Types in Java

Sasireka — Tue, 07 Apr 2026 17:03:35 +0000

Return Type in Java

In Java, the return type means what kind of value a method gives back after it finishes execution.
Syntax:

returnType methodName(parameters) {
    // code
    return value;
}

1) Integer Return Type (int)

public class Sum {

    public static void main(String[] args) {
        Sum num = new Sum();
        int result = num.add(5, 3);
        System.out.println("Sum = " + result);
    }
    public int add(int a, int b) {
        return a + b;
    }
}

int - return type
Method returns an integer value

Output:

2) String Return Type (string)

public class Demo {

    public static void main(String[] args) {
        Demo str = new Demo();
        String name = str.getName();
        System.out.println("Name : " + name);
    }
    public String getName() {
        return "Sasireka";
    }
}

String - return type
Method returns a text (group of characters)

Output:

3) Double Return Type (double)

public class DemoDouble {

    public static void main(String[] args) {
        DemoDouble obj = new DemoDouble();
        double value = obj.getValue();
        System.out.println("Value = " + value);
    }
    public double getValue() {
        return 10.5;
    }
}

double - return type
Method returns a decimal number

Output:

4) Void Return Type (void)

public class DemoVoid {

    public static void main(String[] args) {
        DemoVoid obj = new DemoVoid();
        obj.display();
    }
    public void display() {
        System.out.println("Hello, Welcome!");
    }
}

void - return type
Method does not return anything

Output: