Fundamentals

Compiler vs Interpreter

Compiler	Interpreter
Translates the entire source code into machine code at once, producing a separate executable file (e.g., `.exe`).	Translates and executes the source code line by line without generating a separate executable file.
Compilation happens only once. After that, the program can run without the compiler.	Translation happens every time the program is run, so an interpreter is required each time.
Compiled programs generally execute faster because they run directly on the machine.	Interpreted programs are usually slower because execution happens within the interpreter.

Programming Paradigms

Monolithic Programming
- The entire program is written as a single, large block of code, often in one file, with little or no separation of concerns.
Procedural / Modular / Functional Programming
- The program is divided into smaller, reusable functions or modules that perform specific tasks.
- Example: C language primarily follows the procedural programming paradigm.
Object-Oriented Programming (OOP)
- The program is organized around objects and classes that encapsulate data and behavior.
- Example: C++ supports object-oriented programming.

Header File

Contains declarations of functions, classes, macros, and constants.
Does not contain executable code (usually).
Used by the compiler during compilation.
They're included using #include

#include <iostream>

iostream tells the compiler: “Relax, cout exists. I’ll show you the body later.”

Library File

Contains the definitions / implementations of functions and classes.
Provides the actual compiled code.
Used during linking.
Can be:
- Static library (.a, .lib)
- Dynamic library (.so, .dll)

Example: libstdc++.so → contains the real implementation of cout.

Namespace

Problem:

void fun() {
    cout << "First" << endl;
}

void fun() {
    cout << "Second" << endl;
}

int main() {
    fun();
}

Program will generate error, mentioning fun() is redefined.

Solution:

namespace first
{
    void fun() {
        cout << "First" << endl;
    }
};

namespace second
{
    void fun() {
        cout << "Second" << endl;
    }
};

int main()
{
    fun();          // Invalid Statement, we'll need scope resolution
    first::fun();   // First
    second::fun();  // Second
}

namespace first
{
    void fun() {
        cout << "First" << endl;
    }
};

namespace second
{
    void fun() {
        cout << "Second" << endl;
    }
};

using namespace first;
void main()
{
    fun();          // First - Valid Statement
    first::fun();   // First
    second::fun();  // Second
}

Namespace Summary

A namespace is a named scope that groups identifiers like variables, functions, and classes to avoid name collisions.

namespace math {
    int add(int a, int b) {
        return a + b;
    }
}

std::sort
mylib::sort

Last modified: 08 February 2026