Creating header files
In C++ we have many header files to perform different operations. The advantage in C++ is that the user can create their own header files to suit the requirements of the program. Let us consider a case where too many defined constants are often used. In this case, we can create a header file called "constant.h"
The file will have definition such as
# define phi 3.1428
# define g 9.8
# define e 2.7182
This file can be created using any editor and named as "constant.h".
For example, the following program uses the above said definitions. The header file "constant.h" will enable to substitute for the value of phi, g etc, whereever they are encountered with.
# include <iostream.h>
#include "constant.h"
void main ( )
{
float m, h, r, pe, area ;
cout <<" Enter mass and height " ;
cin >> m>>h ;
pe = m * g * h ;
cout<<" potential energy = "<<pe ;
cout<<" Enter radius : " ;
cin >> r ;
area = 2 * phi * r * r ;
cout <<" Area : "<<area ;
cout <<endl ;
}
In the above program we have included files in two ways.
# include "constant.h"
# include <iostream.h>
The only difference between both expressions is in the directories in which the compiler is going to look for the file. When the file is specified between quotes the file is looked for from the same directory in which the file that includes the directive is, and only in case that it is not there the compiler looks for, in the default directories where it is configured to look for the standard header files.
And when the file name included is enclosed between angle brackets < > the file is directly looked for in the default directories where the compiler is configured to look for the standard header files.
Now let us have another example to find the biggest of a given 'n' numbers using header files.
// header file "big.h"
int max ( int x [ ], int n )
{
int i, m ;
m = x [ 0 ] ;
for ( i = 1; i< n; i++ )
{
if ( m < x [ i ] )
m = x [ i ] ;
}
return m ;
}
// program using big.h
# include "big.h"
#include <iostream.h>
void main ( )
{
int a [ 100 ], n, i, large ;
cout <<"\n Enter how many numbers :" ;
cin >> n ;
cout<<"\n Enter "<<n<<" numbers " ;
for ( i=0; i<n; i++ )
cin >> a [ i ] ;
large = max ( a , n ) ;
cout <<"\n Biggest number is : " << large ;
cout << endl ;
}
Output
Enter how many numbers : 5
Enter 5 numbers
12 45 22 90 67
Biggest number is : 90