A program to explain pointers to functions

#include <stdio.h>
#include <math.h>
#define PI 3.1415926
 
double y(double x)
{
    return (2 * x * x - x + 1);
}
 
double table(double (*f)(), double min, double max, double step)
{
    double a, value;
    for (a = 0; a < max; a += step)
    {
        value = (*f)(a);
        printf("%5.2f %10.4f\n", a, value);
    }
}
 
void main()
{
    printf("Table of y(x) = 2 * x * x - x + 1\n");
    table(y, 0.0, 2.0, 0.5);
 
    printf("Table of y(x) = cos(x)\n");
    table(cos, 0.0, PI, 0.5);
 
    printf("\n");
}