C++ Introduction: Syntax, Compiling and Your First Program

C++ is a compiled language that gives you direct control over memory and performance, which is why it appears in game engines, browsers, databases, trading systems and embedded devices. That control comes with more responsibility than languages like Python or Java, so it pays to understand exactly how your source code becomes a running program. This lesson walks you from nothing to a working program.

What is C++ and how is it different?

C++ is a statically typed, general-purpose language that supports procedural, object-oriented and generic programming. The big difference from Java or Python is how it runs. A C++ compiler translates your code straight into machine code for your processor, producing a native executable. There is no virtual machine and no garbage collector in between, so programs start fast and run fast, but you must manage resources yourself and you must compile separately for each operating system.

Installing a compiler

You need a C++ compiler. The most common free options are g++ (part of GCC) and clang++. On Linux, install g++ with your package manager (for example sudo apt install g++ on Debian or Ubuntu). On macOS, run xcode-select --install to get clang. On Windows, install MinGW-w64 (for example through MSYS2) or use Visual Studio's MSVC compiler. Then verify it from a terminal.

g++ --version

g++ (GCC) 13.2.0

Your version number and wording will differ, which is fine. Anything from GCC 9 or Clang 10 onward handles the C++17 code in this tutorial.

Your first C++ program

Create a file named hello.cpp and type the following. Unlike Java, the file name does not need to match anything inside it.

#include <iostream>

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

Hello, World!

Here is what each line does:

• #include <iostream> is a preprocessor directive that pastes in the declarations for input and output streams. Without it, the compiler does not know what cout is.
• int main() is the entry point. The operating system starts your program here, and the int return value is the exit status. return 0; means success, and for main only, you may omit it.
• std::cout is the standard output stream. << sends values into it, and you can chain several in one statement.
• std::endl ends the line and flushes the output. The string "\n" also ends a line and is slightly cheaper.
• Every statement ends with a semicolon, and blocks are wrapped in braces.

The std:: prefix means "the thing named cout that lives in the standard library namespace std". Namespaces prevent name clashes between libraries. To save typing, beginner examples often add using namespace std; at the top so you can write cout instead of std::cout. That is fine for small programs and the rest of this tutorial does it, but in larger projects and header files prefer writing std:: explicitly.

Compiling and running

Compile with the compiler, naming the output file with -o. The flag -std=c++17 selects the language standard and -Wall -Wextra turn on helpful warnings. Always read the warnings; in C++ many serious bugs show up as warnings first.

g++ -std=c++17 -Wall -Wextra hello.cpp -o hello
./hello

Hello, World!

On Windows the executable is hello.exe, and you run it with hello or .\hello. Behind that one command the toolchain does three things.

Reading input and a tour of the syntax

cin reads from the keyboard, and >> extracts a value into a variable, converting to the variable's type. Note that cin >> name stops at whitespace, so it reads one word.

#include <iostream>
#include <string>
using namespace std;

int main() {
    string name;
    int age;
    cout << "Enter your name: ";
    cin >> name;
    cout << "Enter your age: ";
    cin >> age;
    cout << "Hello, " << name << "! Next year you will be " << age + 1 << "." << endl;
    return 0;
}

Enter your name: Asha
Enter your age: 25
Hello, Asha! Next year you will be 26.

In that session the user typed Asha and 25. The next program shows comments, escape sequences and arithmetic output. Notice that 2 * 49.5 is 99.0 as a double, but cout prints it as 99 because it drops trailing zeros by default.

#include <iostream>
using namespace std;

int main() {
    // A single-line comment
    /* A block comment
       over two lines */
    cout << "Items: " << 3 << "\n";
    cout << "Price: " << 2 * 49.5 << "\n";
    cout << "Tab\tseparated" << "\n";
    cout << "Quote: \"C++\"" << endl;
    return 0;
}

Items: 3
Price: 99
Tab	separated
Quote: "C++"

Common mistakes

• Forgetting the include. Using cout without #include <iostream> fails with error: 'cout' was not declared in this scope (GCC adds a note suggesting the missing header).
• Forgetting `std::` or the using-declaration. The same 'cout' was not declared in this scope error appears when you include the header but write cout without std:: or using namespace std;.
• Missing semicolon. The compiler reports error: expected ';' before 'return', usually pointing at the line after the real mistake.
• Using the wrong stream arrows. Writing cout >> x or cin << x produces a long no match for 'operator>>' error. Remember that the arrows point in the direction the data flows: cout << value and cin >> variable.
• Single quotes for strings. cout << 'Hello'; is a multi-character constant with a warning and prints a number, not text. Use double quotes for strings.
• Ignoring a linker error. undefined reference to 'add(int, int)' means you declared a function but never defined it, or forgot to compile the file that defines it.

How this shows up in interviews and real projects

Interviewers for C++ roles often start with questions such as "what happens when you compile a C++ program?" and "how is C++ different from Java?", and the compile-and-link pipeline above is the honest answer. In real projects you rarely call g++ by hand; build systems such as CMake or Make run it for you, but the same stages and error types apply. When you are ready, browse open roles to see where C++ is used, then continue to C++ Variables and Data Types.