Question 20 (Beginner):
What is the output of this Python code?

x = [1, 2, 3]
y = x
y.append(4)
print(x)

A) [1, 2, 3]
B) [1, 2, 3, 4]
C) [4, 3, 2, 1]
D) Raises an error

#Python #Lists #Variables #Beginner

✅ By: https://t.iss.one/DataScienceQ

✅ **Correct answer: B) `[1, 2, 3, 4]`**

*Explanation:
- `y = x` creates a reference to the same list object
- Modifying `y` affects `x` because they point to the same memory location
- To create an independent copy, use y = x.copy() or y = list(x)*

Top 50 C++ Keywords & Functions

#CPP #Basics #IO

#1. #include <iostream>
A preprocessor directive that includes the input/output stream library.

#include <iostream>

int main() {
    std::cout << "This requires iostream!";
    return 0;
}

This requires iostream!

#2. int main()
The main function where program execution begins.

#include <iostream>

int main() {
    std::cout << "Program starts here.";
    return 0;
}

Program starts here.

#3. std::cout
Used to output data (print to the console).

#include <iostream>

int main() {
    std::cout << "Hello, C++!";
    return 0;
}

Hello, C++!

#4. std::cin
Used to get input from the user.

#include <iostream>
#include <string>

int main() {
    int age;
    std::cout << "Enter your age: ";
    std::cin >> age;
    std::cout << "You are " << age << " years old.";
    return 0;
}

Enter your age: 25
You are 25 years old.

#5. using namespace std;
Tells the compiler to use the std (standard) namespace. Avoids prefixing std:: to every standard function.

#include <iostream>
using namespace std;

int main() {
    cout << "No std:: prefix needed.";
    return 0;
}

No std:: prefix needed.

---
#CPP #DataTypes #Variables

#6. int
Declares an integer variable.

#include <iostream>

int main() {
    int number = 100;
    std::cout << "The number is: " << number;
    return 0;
}

The number is: 100

#7. double
Declares a floating-point number variable (can hold decimals).

#include <iostream>

int main() {
    double price = 19.99;
    std::cout << "The price is: " << price;
    return 0;
}

The price is: 19.99

#8. char
Declares a character variable.

#include <iostream>

int main() {
    char grade = 'A';
    std::cout << "Your grade is: " << grade;
    return 0;
}

Your grade is: A

#9. bool
Declares a boolean variable, which can only have the value true or false.

#include <iostream>

int main() {
    bool isRaining = false;
    std::cout << "Is it raining? " << isRaining; // Outputs 0 for false
    return 0;
}

Is it raining? 0

#10. std::string
Declares a variable that can hold a sequence of characters. Requires #include <string>.

#include <iostream>
#include <string>

int main() {
    std::string greeting = "Hello, World!";
    std::cout << greeting;
    return 0;
}

Hello, World!

---
#CPP #Keywords #Operators

#11. const
Declares a variable as a constant, meaning its value cannot be changed.

#include <iostream>

int main() {
    const double PI = 3.14159;
    std::cout << "The value of PI is: " << PI;
    // PI = 4; // This would cause a compile error
    return 0;
}

The value of PI is: 3.14159

#12. sizeof()
An operator that returns the size (in bytes) of a data type or variable.

#include <iostream>

int main() {
    int myInt;
    std::cout << "Size of int is: " << sizeof(myInt) << " bytes.";
    return 0;
}

Size of int is: 4 bytes.