C++ Program Structure

Every C++ program, no matter how complex, starts with a basic structure. Understanding this structure is crucial for beginners, as it lays the foundation for everything else you’ll learn in C++. In this section, we’ll walk through the essential components of a C++ program and explain the purpose of each line using simple examples.

Example 1: The Simplest C++ Program

hello.cpp

#include <iostream>
 
int main() {
    std::cout << "Hello, world!" << std::endl;
    return 0;
}

Explanation:

#include <iostream> This is a preprocessor directive that tells the compiler to include the input-output stream library. It’s needed for std::cout, which is used to print output.
int main() This is the main function — the entry point of every C++ program. The execution of your program starts here.
{ ... } These curly braces define the body of the main function. All the code inside will be executed when the program runs.
std::cout << "Hello, world!" << std::endl; This line prints the text Hello, world! to the console.
- std::cout is the standard output stream.
- << is the stream insertion operator (used to send data to the output).
- std::endl adds a newline and flushes the output buffer.
return 0; This tells the operating system that the program has ended successfully.

Example 2: Adding Comments and Variables

hello.cpp

#include <iostream>
 
int main() {
    // Declare a variable
    int age = 20;
 
    // Display the value
    std::cout << "Age: " << age << std::endl;
 
    return 0;
}

Explanation:

// Declare a variable This is a single-line comment. Comments are ignored by the compiler and are used to explain code.
int age = 20; This declares an integer variable named age and initializes it with the value 20.
"Age: " << age << std::endl This combines a string with the value of the variable age and prints them together. Output: Age: 20.

Example 3: Using Multiple Statements and Whitespace

hello.cpp

#include <iostream>
 
int main() {
    int a = 5;
    int b = 10;
    int sum = a + b;
 
    std::cout << "Sum: " << sum << std::endl;
 
    return 0;
}

Explanation:

int a = 5; int b = 10; Declares two integer variables a and b.
int sum = a + b; Calculates the sum of a and b, and stores it in another variable sum.
std::cout << "Sum: " << sum << std::endl; Outputs the result of the addition. Output: Sum: 15.
The use of indentation and spacing improves readability but has no effect on program execution.

Summary

A basic C++ program includes:

Component	Description
`#include <iostream>`	Adds standard input/output capabilities
`main()`	The starting point of program execution
`{}`	Defines blocks of code
`std::cout`	Used to display output to the screen
`return 0;`	Indicates successful completion of the program
`//` or `/* ... */`	Used to write comments in the code
Variables	Store and manage data during program execution

Mastering the structure of a C++ program is the first step toward becoming a confident programmer. In the next sections, we’ll explore each part of the language in more depth.

Compiling and Running Comments