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This tutorial will just be an example of a C++ program using multiple files. I will show you one accepted way to organize a program. If you want to check out my other tutorials in this series, here they are:

Part 1: Hello World!

Part 2: Variables

Part 3: Functions

Part 4: if(), else, else if()

Part 5: Loops

Part 6: Arrays

Part 7: Basic Input/Output

Part 9: Sorting Arrays

Part 10: Random Numbers

Part 11: Colored Text in your Terminal

Part 12: Recursion

Part 13: Binary Search

Part 14: 2D Arrays

Part 15: String Processing

Part 16: Binary, Bitwise Operators, and 2^n

Part 17: Pointers

Part 18: Pointer Arithmetic

Part 19: Object Oriented Programming 1 -- Data Structures

Part 20: Object Oriented Programming 2 -- Classes

Part 21: Object Oriented Programming 3 -- Polymorphism

Part 22: Command Line Arguments

Part 23: Header Files

An Accepted Method

There are many ways to code, but I will go over one accepted method. Say you want to build a program with classes and functions for that class. Start with a header file. In the header file, create your classes with the class members and declare any global variables. Do not set any values or build any functions. We will use a separate file for that.

Here is my header file for a Rectangle program (header.h):

#ifndef HEADER_H
#define HEADER_H

class Rectangle
{
    private:
        int height;
        int width;
    public:
        void set_height(int);
        void set_width(int);
        int area();
};

#endif

Now that a header file is made, I will create a separate file (functions.cpp) to build all of the functions:

#ifndef FUNCTIONS_CPP
#define FUNCTIONS_CPP

void Rectangle::set_height(int h)
{
    height = h;
}

void Rectangle::set_width(int w)
{
    width = w;
}

int Rectangle::area(void)
{
    return height * width;
}

#endif

Now that the structure of the program is built, let's implement it by creating the file with main() (main.cpp):

#include <iostream>
#include "header.h"
#include "functions.cpp"

using namespace std;

int main()
{
    Rectangle r;
    r.set_height(5);
    r.set_width(4);

    cout << "Area of rectangle: " << r.area() << endl;

    return 0;
}

This:

• creates a Rectangle object called r
• sets the dimensions with the functions that were declared earlier
• prints:
  • "Area of rectangle: "
  • what r.area() returns (which is the area)

Here is the output:

[cmw4026@omega test]$ g++ main.cpp header.h
[cmw4026@omega test]$ ./a.out
Area of rectangle: 20
[cmw4026@omega test]$

• main.cpp included functions.cpp, so it doesn't have to be listed when compiling

I hope this helped you learn how to build a neatly written program! It is always good to code as neatly as possible and leave many comments when working with others. Leave any suggestions in the comments!

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