📅 Date: Jan 2, 2026
🔥 Topic: Variables, Primitives & Data Types

📦 What are Variables?

Yesterday, I printed static text. But software needs to handle changing data. That's where Variables come in.

Think of a variable as a container or a box in the computer's memory where we store data. Every box needs two things:

  • A Name: To identify it (e.g., age, score).
  • A Type: To tell the computer what kind of data is inside (Number? Text? Decimal?).

🗂️ Data Types in C++

C++ is a "strongly typed" language. This means if I create a box for an integer, I cannot force text into it. Here are the fundamental types I learned today:

  • int: Stores whole numbers (e.g., 25, -10).
  • float / double: Stores decimal numbers (e.g., 9.8, 3.14). Double is just a more precise float.
  • char: Stores a single character in single quotes (e.g., 'A', '$').
  • string: Stores text in double quotes (e.g., "Sahil"). (Requires #include <string>)
  • bool: Stores logical values: true (1) or false (0).

💻 Day 2 Code: Creating a User Profile

To practice this, I wrote a program that stores different types of data for a user profile and prints them out. 

#include <iostream>
using namespace std;

int main() {
    // 1. Integer (Whole Number)
    int age = 19;
    
    // 2. Float (Decimal)
    float cgpa = 8.5;
    
    // 3. Character (Single Letter)
    char grade = 'A';
    
    // 4. Boolean (True/False)
    bool isCoder = true;
    
    // 5. String (Text)
    string name = "Sahil";

    // Displaying the Data
    cout << "--- ID CARD ---" << endl;
    cout << "Name: " << name << endl;
    cout << "Age: " << age << endl;
    cout << "CGPA: " << cgpa << endl;
    cout << "Grade: " << grade << endl;
    
    // Bool prints 1 for true, 0 for false
    cout << "Is Coder? " << isCoder << endl;

    return 0;
}

🧠 Key Takeaway: Memory Size

I also learned that different types take up different amounts of space in memory (RAM).

  • int usually takes 4 bytes.
  • char takes only 1 byte.
  • double takes 8 bytes.

We can check this using the sizeof() function!

💭 Thoughts

Variables make code dynamic. Instead of hardcoding "Sahil", I can now store it in a variable `name` and change it whenever I want. Tomorrow, I plan to look into If/Else Conditionals to make decisions in code.