Introduction to C++

Why this lesson matters

C++ is often chosen when speed, control, and reliability matter: game engines, trading systems, databases, robotics, embedded devices, and parts of AI infrastructure.

If you come from JavaScript or TypeScript, C++ may feel more explicit. You will tell the computer more about your program up front: what types values have, where execution begins, and how code is compiled.

That extra explicitness is the tradeoff: C++ asks for precision, but rewards you with performance and low-level control.

In this first lesson, we will build your starting mental model:

• What C++ is used for
• How C++ code becomes a program
• The shape of a small C++ file
• Basic syntax: output, variables, types, and simple control flow

Later lessons will build on this foundation with object-oriented programming, data structures, algorithms, and file handling.

The big workflow difference

In many web development workflows, you write JavaScript and run it directly in a browser or Node.js runtime.

C++ usually has an extra step: compilation.

A compiler translates your human-readable .cpp file into a machine-runnable program.

source code        compiler           executable
main.cpp    ->     g++/clang++   ->    program you run

That means C++ catches many errors before the program runs. It also means the final program can be highly optimized for the machine running it.

A typical command-line flow looks like:

g++ main.cpp -o app
./app

You do not need to memorize build tools today. Just remember: C++ source code is compiled before it runs.

Your first complete program

Every C++ program needs a place to begin. For a normal console program, that place is the main function.

This example prints two lines and exits successfully.

```cpp
#include <iostream>

int main() {
    std::cout << "Hello, C++!" << std::endl;
    std::cout << "We are learning a fast compiled language." << std::endl;

    return 0;
}
```

What did we just write?

Let's unpack the first C++ program without going too far too fast.

• #include <iostream> gives us access to input/output tools, including std::cout.
• int main() declares the program's starting function.
• { ... } braces group the body of the function.
• std::cout prints text to the console.
• << sends data into the output stream.
• std::endl ends the line and flushes output.
• return 0; means the program finished successfully.

Two syntax habits matter immediately:

1. C++ is generally case-sensitive: main and Main are different.
2. Most statements end with a semicolon: ;

Compared with JavaScript, C++ syntax may look stricter. That strictness helps the compiler understand exactly what you mean.

Which statement best describes how a typical C++ program runs?

C++ wants to know what kind of value you mean

In JavaScript, you might write let price = 42.50 and the runtime tracks the type dynamically.

In C++, variables usually declare their type up front:

• int for whole numbers
• double for decimal numbers
• char for a single character
• bool for true or false
• std::string for text, with the right include

Here is a tiny finance-flavored example: calculating the value of a stock position.

```cpp
#include <iostream>
#include <string>

int main() {
    std::string symbol = "ALGO";
    int shares = 25;
    double price = 18.40;
    double positionValue = shares * price;

    std::cout << "Symbol: " << symbol << std::endl;
    std::cout << "Shares: " << shares << std::endl;
    std::cout << "Position value: $" << positionValue << std::endl;

    return 0;
}
```

Fill in the blank: in a standard C++ console program, execution begins in the _____ function.

Programs need control flow

Most useful programs do not just run one straight line of code. They make decisions and repeat work.

At an introductory level, two core tools are:

• if / else for decisions
• for loops for repetition

Below, we simulate checking latency readings from a trading or AI service. We print whether each reading is acceptable.

```cpp
#include <iostream>

int main() {
    int latenciesMs[] = {12, 48, 95, 31};
    int count = 4;

    for (int i = 0; i < count; i++) {
        std::cout << "Reading " << i << ": " << latenciesMs[i] << " ms - ";

        if (latenciesMs[i] <= 50) {
            std::cout << "OK" << std::endl;
        } else {
            std::cout << "Too slow" << std::endl;
        }
    }

    return 0;
}
```

True or false: in C++, most simple statements, such as variable declarations and return statements, end with a semicolon.

You now have the starting map

You have seen the basic shape of C++:

• C++ source code is usually compiled.
• A program commonly starts at main.
• Output can be printed with std::cout.
• Variables usually declare a type.
• if statements and loops let programs make decisions and repeat work.

This is enough to begin reading small C++ programs and experimenting with your own.

Next, we will move from simple functions into Object-Oriented Programming in C++, where you will learn how C++ organizes related data and behavior into reusable program designs.