Compilation and your first program | C++

A C++ program must be compiled before it runs. The compiler reads source code, checks it, translates it, and produces something the operating system can execute.

Start with one file named main.cpp:

#include <iostream>

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

main is the program entry point. When the executable starts, control enters main.

Compile and run

With clang++ or g++, compile from the directory containing main.cpp:

clang++ -std=c++20 -Wall -Wextra -pedantic main.cpp -o hello
./hello

-std=c++20 asks for C++20 language rules. -Wall -Wextra -pedantic enables useful warnings. -o hello names the output executable.

Warnings matter in C++. Treat them as early help from the compiler.

What the program contains

#include <iostream> asks the preprocessor to make declarations from the standard input/output library visible. Without it, the compiler would not know what std::cout means.

std::cout is an output stream. << sends data into that stream.

return 0; reports success to the operating system. Reaching the end of main also returns 0, but writing it early makes the idea visible.

Statements and expressions

A statement performs an action:

std::cout << "Saved\n";
return 0;

An expression produces a value or names something that can be used as a value:

2 + 3
name
count == 0

C++ programs are mostly declarations, statements, and expressions arranged inside functions and types.

Compile errors are part of the workflow

If you remove the semicolon after return 0, the compiler reports an error. C++ is strict about syntax because it must understand the program before producing machine code.

Compiler errors often point near the problem, not always exactly at it. Read the first error first. Later errors can be side effects of the first one.

What to carry forward

C++ source code must be compiled before it runs
main is the entry point of an executable program
#include makes library declarations visible
statements do work; expressions produce values
warnings are useful feedback, not noise

Next, you will learn how C++ represents values, types, variables, and initialization.