Day 02

Rohit Juyal — Sun, 06 Apr 2025 21:24:36 +0000

Written on: 06 April, 2025.

📝 Comments in C++

We use comments to explain what a code do. It is ignored by compiler and is used for other developers:

// This is a single-line comment

/*
This is a 
multi-line comment
*/

📦 Preprocessor Directives

At the top of most C++ programs, you’ll often see lines starting with #. These are preprocessor directives, and they give instructions to the compiler before the actual compilation starts.

#include <iostream>

This line tells the compiler to include the iostream file — a pre-written file that contains useful code for input and output operations.

💬 Input/Output in C++

To print something on the screen in C++, we use:

std::cout << "Hello, world!" << std::endl;

Let’s break it down:

std stands for standard.
cout is the function used for console output.
<< is the insertion operator (used to send output to the screen).
endl means end line, just like pressing “Enter”, it moves cursor to new line.

Another way of writing is:

using namespace std;

This line allows you to skip writing std:: every time. But be careful! Importing the entire std namespace can be heavy in larger programs. A better approach is:

using std::cout;
using std::endl;

🧠 Namespaces

A namespace is like a region that allow us to group names for variables etc to avoid conflicts. "std" is standard C++ library for names.
We can also create our own namespaces.

Example:

namespace my_own {
    void do_something() {
        // do some thing
    }
}

int main() {
    my_own::do_something(); // calling the function inside the namespace
    return 0;
}

🌐 Real-World Namespace Examples

Here are some common namespaces you’ll see in C++:

std → Standard C++ Library (e.g., std::cout, std::endl)
cv → OpenCV library (e.g., cv::Mat, cv::imread)
Eigen → Eigen library for linear algebra (e.g., Eigen::MatrixXd)

📌 Functions: What Are They?

In simple words, a function is a name given to a block of code that performs a specific task. It allows us to reuse code and makes our programs more organised.

int addNumbers() {
    // code to add numbers
    return 0;
}

💡 Key Point:

Every function returns a value. We use `return 0;` to indicate that the function is executed successfully.

🛠️ Methods: Functions Inside Objects

Methods are also functions, but they belong to objects or classes. I will learn about objects later.

Even the main() function is technically a method. It's the starting point of any C++ program.

📚 Variables

To store data, we use variables.

int abc;       // Declaration
abc = 100;     // Assignment

Or in one line:

int abc = 100; // Initialization

There are certain keywords which we can't use as variable names, as they have meaning in C++.

🎯 Why `main.cpp`?

Big projects often contains many files, so it’s common to name your main file main.cpp. It makes us clear where the program begins execution. This is just a naming convention for better understanding and structuring.

💻✨ Data Types in C++

The data we store in variables, is divided into categories called data types. Each data type tells the compiler what kind of value a variable will hold. This avoids confusion and prevents error.

🔢 `int` – Integer Type

The int data type is used to store whole numbers — that is, numbers without decimal points.

int age = 25;
int year = 2025;
int temperature = -10;

🔒 Constant Values

If you don’t want a variable’s value to change, declare it as const:

const int abc = 231;
// abc = 200;  ❌ This will give an error

✅ Summary

Add comments to keep your code readable.
Use #include to bring in standard or custom files.
Use std::cout or using namespace std for output.
Namespaces help organize and avoid conflicts in code.
Functions do specific tasks and return values.
Methods are functions connected to objects.
int data type is used for storing whole numbers.
Use const to lock variable values.

About me(a little more detail): Hi, I am Rohit. I started my career late in life i.e. last year, right now I am 35. I am currently working in BPO. My aim is to get into HFT. I know it's not a joke & age and other factors not on my side. But let's see how things goes on. A year earlier I was just sitting on my desk unemployed hoping for life to become better. If not that I will be happy trying.

"Hello C++"

Rohit Juyal — Sat, 05 Apr 2025 08:59:34 +0000

Basics of C++

It's an object oriented language
It's statically typed language, meaning we know the data type of the variable (we define it)
We can manage memory in it, as it has concept of pointers
It's a compiled language, compiler converts c++ code into binary
As we can have binary code file in the end, C++ program can be said platform independent i.e. can run anywhere

My first program:

include

int main()
{
std::cout << "Hello World" << std::endl;
return 0;
}

Explanation(what ever I was able to understand):

To run program we need to have pre-written files, iostream is one of that and #include includes that.
std::cout will show "Hello World" on the screen.
Lines inside should end with semi-colon ;

My setup: I am using Linux as pc is old(windows & vscode working slow), I have installed vim and installed g++( it is a compiler and contains files needed to make program). Not that hectic, easy to use. But took me a week to search what is good for me.

DEV Community: Rohit Juyal