Introduction to C++

What is C++?

• C++ is a general-purpose language created by Bjarne Stroustrup as an extension of C with classes.
• It supports procedural, object-oriented, and generic programming.
• Used in systems, games, finance, embedded, compilers, and high-performance apps.

Differences between C and C++

• C++ builds on C ideas but is not a strict superset — some C code needs changes to compile as C++.
• Use this table as a quick map of everyday differences you will meet in the course.

First program

• Save as hello.cpp, then compile with: g++ hello.cpp -o hello and run ./hello (or hello.exe on Windows).

#include <iostream>

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

Deeper rules

• Prefer a modern dialect: compile with -std=c++17 or later unless a project forces an older standard.
• C++ is not a strict superset of C — void* conversions, designated initializers rules, and keyword clashes differ.
• One definition rule (ODR): each non-inline function/variable should have exactly one definition across the program.
• main must return int; falling off the end of main implicitly returns 0 in C++.
• Prefer RAII and the standard library over manual new/delete and C-style arrays for application code.
• Headers vs sources: put declarations in .h/.hpp, definitions in .cpp (templates are a special case).
• Name lookup and overload resolution are compile-time; virtual dispatch is runtime — different costs and rules.
• Undefined behaviour (dangling pointers, out-of-bounds, signed overflow) is not “sometimes wrong” — it is unconstrained.

Hello World with namespace qualification

#include <iostream>

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

Hello with using directive

#include <iostream>
using namespace std;

int main() {
    cout << "Welcome to C++\n";
    return 0;
}