DEV Community: arun Kumar

Mastering Python While Loops: 15 Beginner-Friendly Programs with Code

arun Kumar — Mon, 08 Jun 2026 14:13:38 +0000

Python's while loop allows a block of code to execute repeatedly as long as a condition is true. It is one of the first looping concepts every beginner should learn.

In this article, we'll explore practical examples using while loops.

1. Print 1 Five Times

count = 1

while count <= 5:
    print(1, end=" ")
    count += 1

Output

1 1 1 1 1

2. Print Numbers from 1 to 5

count = 1

while count <= 5:
    print(count, end=" ")
    count += 1

Output

1 2 3 4 5

3. Print Odd Numbers

count = 1

while count < 10:
    print(count, end=" ")
    count += 2

Output

1 3 5 7 9

4. Print Multiples of 3

count = 3

while count <= 15:
    print(count, end=" ")
    count += 3

Output

3 6 9 12 15

4(i). Print Multiples of 3 in Reverse

count = 15

while count >= 3:
    print(count, end=" ")
    count -= 3

Output

15 12 9 6 3

4(ii). Print Even Numbers in Reverse

count = 10

while count >= 2:
    print(count, end=" ")
    count -= 2

Output

10 8 6 4 2

4(iii). Print Odd Numbers in Reverse

count = 9

while count >= 1:
    print(count, end=" ")
    count -= 2

Output

9 7 5 3 1

5. Multiples of 3 and 5 ?

num = 1

while num <= 30:
    if num % 3 == 0 and num % 5 == 0:
        print(num)
    num += 1

Output

15
30

6. Multiples of 3 or 5

num = 1

while num <= 30:
    if num % 3 == 0 or num % 5 == 0:
        print(num)
    num += 1

7. Divisors of a Given Number

num = int(input("Enter a number: "))

i = 1

while i <= num:
    if num % i == 0:
        print(i)
    i += 1

Example

Input: 12
Output: 1 2 3 4 6 12

8. Count of Divisors

num = int(input("Enter a number: "))

i = 1
count = 0

while i <= num:
    if num % i == 0:
        count += 1
    i += 1

print("Number of Divisors:", count)

9. Prime Number Check

num = int(input("Enter a number: "))

i = 1
count = 0

while i <= num:
    if num % i == 0:
        count += 1
    i += 1

if count == 2:
    print("Prime Number")
else:
    print("Not a Prime Number")

10. Perfect Number Check

num = int(input("Enter a number: "))

i = 1
sum_div = 0

while i < num:
    if num % i == 0:
        sum_div += i
    i += 1

if sum_div == num:
    print("Perfect Number")
else:
    print("Not a Perfect Number")

Example

6 = 1 + 2 + 3

11. Print 1 3 5 7 9 2 4 6 8 10 Using a Single Loop

i = 1

while i <= 10:
    if i <= 5:
        print(2 * i - 1, end=" ")
    else:
        print(2 * (i - 5), end=" ")
    i += 1

Output

1 3 5 7 9 2 4 6 8 10

12. Factorial of N Number

num = int(input("Enter a number: "))

fact = 1
i = 1

while i <= num:
    fact *= i
    i += 1

print("Factorial =", fact)

Example

5! = 120

13. Sum of First n Numbers

n = int(input("Enter a number: "))

sum = 0
i = 1

while i <= n:
    sum += i
    i += 1

print("Sum =", sum)

Example

1 + 2 + 3 + 4 + 5 = 15

14. Print First 5 Prime Numbers

count = 0
n = 2

while count < 5:
    i = 1
    divisors = 0

    while i <= n:
        if n % i == 0:
            divisors += 1
        i += 1

    if divisors == 2:
        print(n, end=" ")
        count += 1

    n += 1

Output

2 3 5 7 11

15. Sum of First 5 Prime Numbers

count = 0
n = 2
total = 0

while count < 5:
    i = 1
    divisors = 0

    while i <= n:
        if n % i == 0:
            divisors += 1
        i += 1

    if divisors == 2:
        total += n
        count += 1

    n += 1

print("Sum of first 5 prime numbers:", total)

Output

Sum of first 5 prime numbers: 28

Understanding Constructors in Java: A Beginner's Guide

arun Kumar — Tue, 02 Jun 2026 17:31:09 +0000

Java is one of the most widely used object-oriented programming languages, and constructors play an important role in creating and initializing objects. If you're new to Java, understanding constructors is essential because they help set up an object's initial state when it is created.

What is a Constructor?

A constructor is a special method in Java that is automatically called when an object of a class is created. Its main purpose is to initialize the object's data members.

Unlike regular methods, constructors have the same name as the class and do not have a return type.

Why Do We Need Constructors?

Constructors help initialize objects with default or user-defined values. Without constructors, you would need to assign values manually after creating every object.

Benefits of Constructors

Automatically initializes object data.
Reduces repetitive code.
Improves code readability.
Makes object creation easier.
Supports object-oriented programming principles.

Example of a Constructor
class Student {

String name;

Student() {
    name = "Arun";
}

void display() {
    System.out.println(name);
}

public static void main(String[] args) {
    Student s = new Student();
    s.display();
}

}
Output
Arun

In this example, the constructor assigns the value "Arun" to the name variable when the object is created.

Types of Constructors in Java
1. Default Constructor

A constructor that does not take any parameters is called a default constructor.

class Demo {
Demo() {
System.out.println("Default Constructor Called");
}
}
2. Parameterized Constructor

A constructor that accepts parameters is called a parameterized constructor.

class Student {

String name;

Student(String n) {
    name = n;
}

public static void main(String[] args) {
    Student s = new Student("Arun");
    System.out.println(s.name);
}

}
Output
Arun

Parameterized constructors allow different objects to be initialized with different values.

Rules for Creating Constructors

Constructor name must be the same as the class name.
Constructors do not have a return type.
Constructors are called automatically when an object is created.
A class can have multiple constructors (Constructor Overloading).

Constructor Overloading Example
class Student {

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

Student(String name) {
    System.out.println("Student Name: " + name);
}

public static void main(String[] args) {
    new Student();
    new Student("Arun");
}

}
Output
Default Constructor
Student Name: Arun

Understanding Method Overloading in Java

arun Kumar — Tue, 02 Jun 2026 07:06:38 +0000

Java is one of the most popular object-oriented programming languages, and one of its powerful features is Method Overloading. Method overloading allows developers to create multiple methods with the same name within the same class, as long as their parameter lists are different. This feature improves code readability, reusability, and flexibility.

What is Method Overloading?

Method overloading is a concept in Java where two or more methods share the same name but differ in the number, type, or order of parameters. The Java compiler determines which method to execute based on the arguments passed during the method call. Because this decision is made during compilation, method overloading is also known as Compile-Time Polymorphism.

Why Use Method Overloading?

Method overloading helps developers write cleaner and more intuitive code. Instead of creating separate method names for similar operations, a single method name can be used for different types of inputs. This reduces complexity and makes programs easier to understand and maintain.

Benefits of Method Overloading

Improves code readability.
Increases code reusability.
Reduces the need for multiple method names.
Supports compile-time polymorphism.
Makes programs easier to maintain.

Example of Method Overloading

class Calculator {

void add(int a, int b) {
    System.out.println("Sum: " + (a + b));
}

void add(int a, int b, int c) {
    System.out.println("Sum: " + (a + b + c));
}

void add(double a, double b) {
    System.out.println("Sum: " + (a + b));
}

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

    obj.add(10, 20);
    obj.add(10, 20, 30);
    obj.add(10.5, 20.5);
}

}

Output
Sum: 30
Sum: 60
Sum: 31.0

Types of Method Overloading

Changing the Number of Parameters

A method can be overloaded by changing the number of parameters.

void display(int a) { }
void display(int a, int b) { }

Changing the Data Type of Parameters

A method can also be overloaded by changing the data type of parameters.

void display(int a) { }
void display(double a) { }

Rules of Method Overloading

Methods must have the same name.
Methods must have different parameter lists.
Return type alone cannot differentiate overloaded methods.
Overloading can occur in the same class.

Python Basics: Addition, Multiplication, and Factorial of First n Numbers

arun Kumar — Tue, 26 May 2026 14:59:54 +0000

Addition of First n Numbers

The addition of the first n numbers program is used to calculate the total sum of numbers from 1 to n. This program helps beginners understand how loops and variables work in Python. Using a while loop, the program repeatedly adds numbers until the condition becomes false. For example, if n = 5, the result will be 15.

n = 5
i = 1
total = 0
while i <= n:
total = total + i
i = i + 1
print("Sum =", total)

Multiplication of First n Numbers

The multiplication of the first n numbers program multiplies all numbers from 1 to n. It teaches students how repeated multiplication works using loops. The result for n = 4 will be 24 because 1 × 2 × 3 × 4 = 24. In this program, the initial value starts from 1.

n = 4
i = 1
product = 1

while i <= n:
product = product * i
i = i + 1

print("Product =", product)

Factorial of a Number

The factorial of a number means multiplying all positive integers from 1 up to that number. It is represented using !. For example, 5! = 120. Factorial programs are important in mathematics and computer science. A while loop can be used to calculate factorial easily in Python.

n = 5
i = 1
fact = 1

while i <= n:
fact = fact * i
i = i + 1

print("Factorial =", fact)

Understanding React, SPA & MPA

arun Kumar — Fri, 17 Apr 2026 05:32:31 +0000

What is React?

React is a popular JavaScript library used to build user interfaces, especially for modern web applications. It allows developers to create reusable components, making code more organized and efficient.

🔹 Why Use React?

React is widely used because it simplifies the development process and improves performance.

Key Benefits:
Reusable components
Faster updates with Virtual DOM
Easy to learn and use
Strong community support
Smooth and interactive user experience

🔹 What is SPA (Single Page Application)?

A Single Page Application (SPA) loads only one HTML page and dynamically updates content without refreshing the entire page.

Examples:
Gmail
Instagram
Advantages:
Faster navigation
Better user experience
No full page reload

🔹 What is MPA (Multi Page Application)?

A Multi Page Application (MPA) loads a new page from the server every time the user navigates.

Examples:
Amazon
Flipkart
Advantages:
Good for large websites
Clear structure with multiple pages

My First Calculator Project with HTML, CSS & JavaScript

arun Kumar — Sat, 04 Apr 2026 12:30:50 +0000

Building My First Calculator using HTML, CSS & JavaScript

Introduction

In this project, I built a simple calculator using HTML, CSS, and JavaScript. It was a great experience because I got to see how a small web application is created from scratch. If you are learning front-end like me, this project is really helpful and fun to build.

What I Learned

While building this calculator, I understood how HTML is used to create the structure of a page. I used buttons and an input box to design the calculator layout. It gave me a clear idea of how user interfaces are built.

Using CSS, I made the calculator look clean and simple. I centered it on the screen, added colors, spacing, and some button effects. This helped me understand how design improves the user experience.

JavaScript made everything work. I learned how to handle button clicks, update the display, and perform calculations. Using functions like adding values, clearing, and deleting made the project more interactive.

Features

My calculator can do basic operations like addition, subtraction, multiplication, and division. It also has clear and delete options, supports decimal numbers, and responds when buttons are clicked.

Challenges

I faced some small challenges like handling inputs properly and understanding how the calculation works. But solving them helped me learn better and improve my coding skills.

Conclusion

This project helped me understand how HTML, CSS, and JavaScript work together. It also gave me confidence to build more projects in the future.

Final Thoughts

Building this calculator was simple but very useful for learning. If you are a beginner, I suggest you try this project—it will really help you improve.