How to add a user defined function to a library function:

Here we are going to create a function for factorial of a the given number:

Step 1:

First create the definition of the program and save it with name fact .c

 Int factorial(int num)
{
int  f=1,I;

For(i=1;i<=num;i++)

{  

            F=f*I;

}
return (f);
}

Step 2:

Compile “fact.c” file by using Alt + F9 keys (in turbo C).

step 3:

“fact.obj” file would be created which is the compiled form of “fact.c” file.

Step 4:

Then for adding your function to the library function type the code given below:

c:\> tlib math.lib + c:\ fact.obj
+ means adding c:\fact.obj file in the math library.
We can delete this file using – (minus){c:\> tlib math.lib - c:\ fact.obj}.

Step 5:        

Create a file “fact.h” & declare prototype of fact() function like below.
int factorial (int num);
Now fact.h file containing prototype of function “factorial”.

Step 6:

Let us see how to use our newly added library function in a C program.

# include <stdio.h>

// Including our user defined function.

# include “c:\\factorial.h”    

int main ()

{

       int f,n;

        prinntf(“enter any number”);   //message to the user

        scanf(“%d”,&n);                //receiving input from user

                                      // calling function from library

       f = factorial (n);

       printf ("factorial = %d \n", f);

        return 0;

}