# Tutorial: NP Library Header Files

## Introduction

You will learn how to create and maintain NP library header files

* Declare all your functions in `myNP_tutorial.h`
* Define all your functions in `myNP_tutorial.c`
* Include your library in main source `C_createHeader_example.cpp`

  > Don't worry about the file extension of \*.cpp or \*.c
  >
  > You can use either extension with Visual Studio for Numerical Programming course

***

## Step 1. Create Workspace Folder

### Create a local directory for programming

We will create the main directory under

**C:\Users\yourID\source\repos**

> e.g. **C:\Users\ykkim\source\repos**

You can search for 'repos' in window menu

![image](https://user-images.githubusercontent.com/38373000/185348195-07f482ba-3aac-4fc8-8298-9928f06fc534.png)

This is where your assignment projects should be located.

For this tutorial, let us create the new workspace directory as

* Name the directory as "**NP**"

  > A name that clearly shows the course name

For this course, create the workspace sub-directory as

* **..\NP\tutorial**
* **..\NP\include**
* **..\NP\assignment**
* **..\NP\data**
* **..\NP\test**

> e.g.
>
> **C:\Users\ykkim\source\repos\NP\tutorial**
>
> **C:\Users\ykkim\source\repos\NP\include**

##

## Step 2. Create a tutorial C-prog Project

Under **`..\NP\tutorial`** directory, create a new folder named as **`TU_CreateHeader`**

* i.e.: `C:\Users\yourID\source\repos\NP\tutorial\TU_CreateHeader`

Create a new empty project in Visual Studio Community

* Name the project as **`TU_createHeader`**

Create a new C/C++ source file for main()

* Name the source file as **`TU_createHeader_example.cpp`**

Paste the following code

```cpp
// TU_createHeader_example.cpp 

#include "stdio.h"
#include "stdlib.h"

// Library include path will be modified at the end of the tutorial
// #include "myNP_tutorial.h"


void printVec(double* vec, int row);

int main(int argc, char* argv[])
{
	double x[3] = { 1, 2, 3 };
	int x_size = sizeof(x)/sizeof(double);
	printVec(x, x_size);
}


void printVec(double* vec, int size)
{
	for (int i = 0; i < size; i++)
		printf("Vector[%d] = %.1f \n", i, vec[i]);
	printf("\n");
}
```

Compile and Run the program.

It should display the vector `x[]` values properly.

## Step 3. Create library header files

Under the directory of `\include`**,** create new files or copy `myNP_tutorial.cpp` and `myNP_tutorial.h`.

* **`C:\Users\yourID\source\repos\NP\include`**
* You can paste codes below
* or[ You can download source files here](https://github.com/ykkimhgu/Tutorial-C-Program/tree/main/createHeader)

{% hint style="info" %}
Do not make duplicates of library header files. Keep updating the library header file as you do assignments.
{% endhint %}

{% tabs %}
{% tab title="myNP\_tutorial.h" %}

```cpp
/* myNP_tutorial.h */
#ifndef		_MY_NP_H		// use either (#pragma once) or  (#ifndef ...#endif)
#define		_MY_NP_H

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

extern void printVec(double* vec, int row);

#endif
```

{% endtab %}

{% tab title="myNP\_tutorial.cpp" %}

```cpp
/* myNP_tutorial.cpp */

#include "myNP_tutorial.h"

void printVec(double* vec, int size)
{
	for (int i = 0; i < size; i++)
		printf("Vector[%d] = %.1f \n", i, vec[i]);
	printf("\n");
}
```

{% endtab %}
{% endtabs %}

Your library header files, and project source files should be located as

![image](https://github.com/user-attachments/assets/fe090792-6a6f-44da-80b2-1674848c7fae)

##

## Step 4. Include your library header files in VS code

1. 솔루션 탐색기(Solution Explorer) > 헤더파일 > 추가 > 기존항목
2. `../NP/include/` 폴더에서 `myNP_tutorial.h`, `myNP_tutorial.cpp 선택`

![image](https://github.com/user-attachments/assets/aa4a0aeb-14ef-4ead-80b1-3f8a450172bf)

3\. Modify the header file include path

![image](https://github.com/user-attachments/assets/04fdd643-27e8-4cc4-9019-fc24e04eda2b)

##

## Step 5. Include your Header files in the main code

In the above main() program, include your header library by finding the path.

Now, you need to **delete** the function definition of `printVec()` in main(), for we have included the function from the header library file.

The main source file should be modified as

```cpp
/*  TU_createHeader_example.cpp  */

#include "stdio.h"
#include "stdlib.h"

// Change the Include path 
#include "../../include/myNP_tutorial.h"   // Find the location of header files
// #include "myNP_tutorial.h"   // if the PATH is already Included in Project


void printVec(double* vec, int row);

int main(int argc, char* argv[])
{

	double x[3] = { 1, 2, 3 };
	int x_size = sizeof(x)/sizeof(double);

	printVec(x, x_size);

}

// void printVec() definition is deleted in this file
```

Compile and run the program.