C++

• Introduction
• Getting Output
• Datatype
• Variable Declaration
• Operator
• String Concatenation
• Getting input from user
• Working on Angles
• Escape Sequence
• Conditional Statements
• If statement
• Switch statement
• Loop
• While Loop
• For Loop
• Do While Loop
• Array
• Foreach Loop
• Multi dimensional array
• Nested Loop
• Jump Statements
• String Handling Function
• Methods or Functions
• Passing Parameter
• Method Overloading
• Void Method
• Returning Method
• Class
• Creating New Instance
• Constructor
• Constructor Overloading
• Destructor
• Inheritance
• Multi Level Inheritance
• Multiple Inheritance
• Sealed Class
• Pointers
• Upcasting
• Virtual Method
• Pure Virtual Method
• Enum
• Inline Function
• Validation of data
• Virtual Destructor
• Namespace
• Header File
• Exception Handling
• File Handling

Header File

So far we've written lot of codes. We can write all those code inside a single header file so that it can used in multiple .cpp projects. Header files contains definitions of functions that we can include or import using a preprocessor directive #include. It also gives us the benefit of reusing the functions that are declared in header files to different .cpp files and including a header file is way easier than writing the implementations. There are 2 types of header files in c++, let us study those with definition

Standard library header files - The header files that are already present in the compile of C++.
User-defined header files - The header files created by the user.

So far we used something called #include <iostream> where iostream is a Standard library header file which stands for input and output stream used to take input with the help of “cin” and “cout” respectively. The syntax to include each header file will be different as we use <> for Standard library header files and " " for User-defined header files(Refer below syntax).

Syntax
#include <headerFileName> (To include Standard library header files)
#include "headerFileName" (To include user-defined header files)

STEPS TO FOLLOW:
1. Open new Visual Studio Console App project.
2. You will find Solution Explorer window in the Right Hand side, if not go to top menu choose View - Solution Explorer.
3. Inside solution explorer there will be a folder called Header Files. Right click that and click Add - New Item.

4. Once after 3rd step, New window will open. In the Left hand side choose Header File(.h) give name in the below with .h extension, click ADD.

5. Now a new header file will be created inside Header Files folder(Exact file location is inside current project folder location). Open that file
6. We are all set, Its time to write code inside our header file.

NOTE
Inside header file, we'll have something called #pragma once, which is used to avoid multiple inclusions. If a same header file included multiple times, #pragma once will simply neglect the duplicated one.

CODE

EG 1 . Creating a method inside newly created header file. including it in a different project.

#pragma once
int cube(int number) {
    return number * number * number;
}


Once after writing above code, save header file. Open the current project location where you will find the newly created header file.

Create a new Console App project. Inside that folder location copy paste this header file. Now whatever code we written inside this FirstHeaderFile.h is available in newly created project also. The only step what we need to follow here is, we need include FirstHeaderFile.h inside current project using #include. Just follow the below codes to see how to include newly created header file and how to access method present inside it.

#include <iostream>
#include "FirstHeaderFile.h"

using namespace std;
int main() {
    cout << "The cube value of 9 is " << cube(9) << endl;
}


OUTPUT
The cube value of 9 is 729

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Exercises
1. Create a header file with Degree2Radian(), Radian2Degree(), Square(), FindindPrimeNumber() methods and try to access it in a different project.

(Click Here, For more exercises)