Question 1

What are the basic operations on arrays and strings in data structures? Provide examples in a programming language of your choice to demonstrate these operations.

Accepted Answer

Arrays and strings are fundamental data structures that store collections of elements. In most programming languages, arrays are fixed in size, while strings are typically treated as arrays of characters.

Basic array operations include:
1. Insertion: Adding an element at a specific index.
2. Deletion: Removing an element from a specific index.
3. Traversal: Accessing each element for processing.

Here’s an example in Python demonstrating these operations:
```python
def array_operations(arr, element, index):
    # Insertion
    arr.insert(index, element)
    # Deletion
    arr.pop(index)
    # Traversal
    for i in arr:
        print(i)

arr = [1, 2, 3, 4, 5]
array_operations(arr, 10, 2)  # Insert 10 at index 2
```

Basic string operations include:
1. Concatenation: Joining two strings together.
2. Substring extraction: Getting a substring from a string.
3. Length calculation: Finding the number of characters in a string.

Example in Python:
```python
def string_operations(str1, str2):
    # Concatenation
    combined = str1 + str2
    # Substring extraction
    substring = combined[1:5]
    # Length calculation
    length = len(combined)
    return combined, substring, length

result = string_operations('Hello', 'World')
print(result)  # Output: ('HelloWorld', 'ello', 10)
```

Question 2

Explain and implement the four pillars of Object-Oriented Programming: Encapsulation, Abstraction, Inheritance, and Polymorphism. Provide code examples for each.

Accepted Answer

```java
// Encapsulation
class Employee {
    private String name;
    private double salary;

public Employee(String name, double salary) {
        this.name = name;
        this.salary = salary;
    }

public String getName() {
        return name;
    }

public double getSalary() {
        return salary;
    }
}

// Abstraction
abstract class Shape {
    abstract void draw();
}
class Circle extends Shape {
    void draw() {
        System.out.println("Drawing Circle");
    }
}

// Inheritance
class Manager extends Employee {
    private String department;

public Manager(String name, double salary, String department) {
        super(name, salary);
        this.department = department;
    }

public String getDepartment() {
        return department;
    }
}

// Polymorphism
class Animal {
    void sound() {
        System.out.println("Animal makes sound");
    }
}
class Dog extends Animal {
    void sound() {
        System.out.println("Dog barks");
    }
}

public class Main {
    public static void main(String[] args) {
        Employee emp = new Employee("John", 50000);
        Manager mgr = new Manager("Alice", 70000, "HR");
        Animal myDog = new Dog();
        System.out.println(emp.getName() + " earns " + emp.getSalary());
        System.out.println(mgr.getName() + " manages " + mgr.getDepartment());
        myDog.sound();
    }
}
```

Question 3

Implement a simple banking system in Java that supports account creation, deposit, and withdrawal functionalities. Include error handling for insufficient funds and invalid operations.

Accepted Answer

```java import java.util.HashMap; import java.util.Map; class Account { private String accountNumber; private double balance; public Account(String accountNumber) { this.accountNumber = accountNumber; this.balance = 0.0; } public void deposit(double amount) { if (amount > 0) { balance += amount; System.out.println("Deposited: " + amount); } else { System.out.println("Invalid deposit amount."); } } public void withdraw(double amount) { if (amount > 0 && amount <= balance) { balance -= amount; System.out.println("Withdrawn: " + amount); } else { System.out.println("Insufficient funds or invalid withdrawal amount."); } } public double getBalance() { return balance; } } class BankingSystem { private Map accounts = new HashMap<>(); public void createAccount(String accountNumber) { if (!accounts.containsKey(accountNumber)) { accounts.put(accountNumber, new Account(accountNumber)); System.out.println("Account created: " + accountNumber); } else { System.out.println("Account already exists."); } } public Account getAccount(String accountNumber) { return accounts.get(accountNumber); } } public class Main { public static void main(String[] args) { BankingSystem bankingSystem = new BankingSystem(); bankingSystem.createAccount("12345"); Account account = bankingSystem.getAccount("12345"); account.deposit(500); account.withdraw(200); System.out.println("Balance: " + account.getBalance()); } } ```

Question 4

How do components and props work in React, and how can they be effectively utilized in a PhonePe project?

Accepted Answer

In React, components are the building blocks of the application, representing UI elements. Props (short for properties) are how data is passed from one component to another. They are read-only and allow components to be dynamic and reusable. Here’s a simple example demonstrating components and props: ```javascript import React from 'react'; // A functional component that receives props const UserProfile = ({ name, age }) => { return (

{name}

Age: {age}

); }; // Parent component const App = () => { return (

); }; export default App; ``` In this example, the `UserProfile` component receives `name` and `age` as props from the `App` component. This allows for the creation of multiple user profiles without duplicating code, promoting reusability. Edge Cases: Ensure to validate the props using PropTypes or TypeScript to prevent unexpected data types from causing runtime errors.

Question 5

Write an SQL query to retrieve the names of all customers who have placed more than 5 orders from a `customers` table and an `orders` table, using JOIN and GROUP BY.

Accepted Answer

```sql
SELECT c.name
FROM customers c
JOIN orders o ON c.customer_id = o.customer_id
GROUP BY c.customer_id, c.name
HAVING COUNT(o.order_id) > 5;
```

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