1.1 — C++ Basics & Program Structure

Let's start with the foundation. Every C++ program follows a basic structure that you need to understand cold before anything else makes sense.

The Basic Structure

#include <iostream>      // Preprocessor directive - includes input/output library
using namespace std;      // Lets us use 'cout' instead of 'std::cout'

int main() {               // Entry point - execution ALWAYS starts here
    cout << "Hello, World!" << endl;   // Statement 1
    return 0;               // Tells OS the program ended successfully
}

Breaking It Down Piece by Piece

1. Preprocessor Directives (#include)

• Lines starting with # are processed before compilation, by the preprocessor.
• #include <iostream> pulls in the Standard Input/Output stream library so you can use cout, cin, etc.
• Other common ones: <string>, <vector>, <cmath>.

2. Namespaces (using namespace std;)

• All standard library names (cout, cin, string, etc.) live inside a namespace called std.
• Without this line, you'd have to write std::cout every time.
• (We'll cover namespaces properly at 1.33 — for now just know it avoids repetitive prefixing.)

3. The main() function

• Every executable C++ program must have exactly one main() function.
• It's the entry point — the OS calls main() first when you run the program.
• Return type is int: it returns a status code to the operating system.
  • return 0; → success
  • return 1; (or any non-zero) → some error occurred

4. Statements & Semicolons

• Each instruction ends with a semicolon ;.
• Forgetting it is the #1 beginner compile error.