Use of pointers to function

Program 55) Write a program that uses a function pointer as a function arguement.
A program to print the function values over a given range of values. The printing is done by the function table by evaluating the function passed to it by the main.

With table, we declare the parameter f as a pointer to a function as follows:
                          double  (* f) () ;
The value returned bythe function is of type double. When table is called in the statement
                         table (y, 0.0, 2, 0.5) ;
we pass a pointer to the function y as the first parameter of table. Note that y is not followed by a parameter list.
During the execution of table, the statement
                                value = (* f) (a) ;
calls the function y which is pointed to by f, passing it the parameter a. Thus the function y is evaluated over the range 0.0 to 2.0 at the intervals of 0.5.
    Similarly the call
                              table (cos, 0.0, PI, 0.5) ;
passes a pointer to cos as its first parameter and therefore, the function table evaluates the value of cos over the range 0.0 to PI at the intervals of 0.5.

                                     PROGRAM

#include <math.h>
#define  PI  3.1415926
double y (double) ;
double cos (double) ;
double table (double (*f) (), double, double, double) ;

main ( )
 {
       printf ("Table of y(x) = 2 * x * x - x + 1\n\n") ;
       table (y, 0.0, 2.0, 0.5) ;
       printf ("\nTable of cos (x) \n\n") ;
       table (cos, 0.0, PI, 0.5) ;
 }
double table (double (*f) (), double min, double max, 
                                             double max, double step)
{       double a, value ;
        for (a = min; a <= max; a += step)
        {
                value  = (*f) (a) ;
                printf ("%5.2f  %10.4f\n", a, value) ;
        }
}
double y (double x)
{
           return (2 * x * x - x + 1) ;
}

Output:                Table of y (x) = 2 * x * x - x + 1
                                0.00              1.0000
                                0.50              1.0000
                                1.00              2.0000
                                1.50              4.0000
                                2.00              7.0000
                           Table of cos (x)
                                0.00              1.0000
                                0.50              0.8776
                                1.00              0.5403
                                1.50              0.0707
                                2.00             -0.4161
                                3.00             -0.9900