Lesson 1 - Your First C++ Program

Prerequisites

• None. This is the first lesson in the beginner path.
• A working C++ setup that can build and run a single source file.

Note

This path assumes your C++ environment is already installed and working. Setting up a compiler, an editor, or an operating system is outside this path, so no build commands are given here. Use whatever build-and-run action your existing setup already provides.

What You Will Learn

• The stages that turn C++ source text into a running program.
• What a complete, minimal C++ program looks like.
• How to make a program print one exact line of text.

From Source To A Running Program

C++ is a compiled language. The text you write is not what the machine runs. Your text passes through a fixed sequence of stages first.

source
  |
  | compile
  v
object code
  |
  | link
  v
executable
  |
  | run
  v
output

Read the stages like this:

• source is the C++ text you write and save in a file
• compile translates one source file into machine instructions
• object code is that translated result, which is not runnable on its own
• link joins your object code with the standard library code it depends on
• executable is the finished program file the system can start
• run starts the executable, which then produces output

Two ideas from this sequence matter for the rest of the path:

• A mistake in your text is usually reported at the compile stage, before anything runs
• Nothing you write produces output until the run stage is reached

Worked Example

This is a complete program. Nothing is missing from it.

#include <iostream>

int main() {
    std::cout << "Hello, CP4CPP!\n";
    return 0;
}

Output:

Hello, CP4CPP!

Each part has a job:

• #include <iostream> brings in the standard input and output declarations. Without it, std::cout is not declared.
• int main() declares the function where the program starts. Every program in this path has exactly one main.
• { and } mark the start and end of the body of main.
• std::cout is the standard output stream. The std:: prefix says the name comes from the standard library.
• << sends the value on its right into the stream on its left.
• "Hello, CP4CPP!\n" is the text to print. The \n is one newline character, so the output ends with a line break.
• return 0; ends main and reports success to the system.

Exercise

Write a complete program that prints exactly one line:

I compiled my first C++ program.

Start from the worked example and change only the text between the quotation marks. Keep #include <iostream>, int main(), the \n, and return 0; exactly as they are.

Exercise Check

Expected output:
I compiled my first C++ program.

This program reads no input, so there is nothing to type when it runs.

Check these before moving on:

• The line matches the expected output exactly, including the final period
• There is no extra text before or after the line
• The program reached the run stage, which means compiling and linking both succeeded

Next Steps

You can now produce fixed output. The next lesson keeps this program shape and adds input, named variables, and arithmetic, so the output depends on what the program is given.