Program Structure

Understanding the basic structure of a program

Structure of a C++ Program

In this section we will study the basic structure of a C++ program and get familiar with the key components that make up any program.

Basic program structure

Every C++ program consists of several key components:

Preprocessor directives

Preprocessor directives start with the # symbol and are processed before compilation begins:

In later modules we will get to know other libraries, such as <string> for working with strings and <vector> for working with collections of data. For now <iostream> is all we need.

Namespace

This line allows us to use standard C++ objects (such as cout, cin) without the std:: prefix. Without it we would have to write std::cout instead of cout.

The main() function

The main() function is the entry point of the program:

• int — indicates that the function returns an integer
• main — the name of the function (required in every program)
• () — the parameter list (empty in this case)
• {} — the function body, where the executable code lives
• return 0; — returns 0, meaning the program executed successfully

Operators and expressions

Inside the main() function we write operators and expressions:

Comments

Comments help explain the code and do not affect program execution:

Coding rules

1. Every statement ends with a semicolon ;

2. C++ is case-sensitive

Main and main are different names. A program without a lowercase main function will not run:

3. Spaces and line breaks are ignored by the compiler, but they affect readability — write neatly.

Both versions below are identical to the compiler, but not to a human:

4. Variable and function names may contain letters, digits, and underscores, but cannot start with a digit:

This basic structure is the foundation for all C++ programs we will study going forward.