Example of function pointers in C

f_ptr_ex.c

#include <math.h>
#include <stdio.h>
#include <stdlib.h>

#define PI 3.141592653589793

double f_a(double x) { return x*x + sin(x) - PI; }

typedef double (*MATH_FUNCTION)(double);

double calculate_f_0(double (*f)(double))
{
    return (*f)(0);
}

int main()
{
    MATH_FUNCTION F = &f_a;

    printf("%.15e\n", calculate_f_0(&f_a));
    printf("%.15e\n", calculate_f_0(F));

    return 0;
}