Structure of a C++ Program

C++ is a powerful and versatile programming language widely used for developing various applications and software systems. To write effective C++ programs, it is essential to understand and follow a specific structure. This article will guide you through the structure of a typical C++ program.


A C++ program consists of one or more functions, which are written to perform specific tasks. These functions are combined into a hierarchical structure that starts with the main() function. The main() function serves as the entry point of a C++ program, where the execution begins and ends.


A basic C++ program is structured as follows:

// Header files

// Preprocessor directives

// Function prototypes

// Main function

// Function definitions

Let's dive deeper into each section of the structure.

Header Files

The first part of a C++ program usually includes one or more header files. Header files provide necessary declarations and definitions for the functions used in the program. They allow you to include external libraries or modules, which provide additional functionality to your program. For example, you may include the <iostream> header file to use standard input and output operations.

#include <iostream>

Preprocessor Directives

The next section of a C++ program is the preprocessor directives. These directives are processed by the preprocessor before the compilation phase. They are used to define constants, create macros, and perform conditional compilation.

#define PI 3.14

Function Prototypes

Function prototypes declare the functions that are defined later in the program. They provide information about the function name, return type, and parameters. Prototypes are essential when functions are called before their definitions to inform the compiler about the function's existence.

int sum(int a, int b);

Main Function

The main() function is where the execution of a C++ program begins and ends. It acts as the primary control point of the program. All other functions may be called or executed within the main() function. The main() function has a return type of int to indicate the status of program execution.

int main() {
    // Function calls or other code
    return 0;

Function Definitions

Finally, function definitions contain the actual implementation of the declared functions. These definitions provide the code that executes when the function is called. Function definitions should be placed after the function prototypes and the main function.

int sum(int a, int b) {
    return a + b;


Understanding the structure of a C++ program is crucial for writing well-organized and efficient code. By following this structure, you can create robust and readable programs. Remember that each section plays a vital role in composing a functional C++ program. Take your time to learn and practice this structure, and you will be on your way to becoming a skilled C++ programmer.

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