Demo: function pointer

Reinhard

Hi,
one of C's strenght are function pointers.
Here a small demo for propgcc.

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

// this is a new type, a pointer to a function
typedef double (*function_pointer)(double x);

/**
* Differentiate any given Function at point x.
* @param f: function to differentiate, thats a pointer to a function
* @param x: double the argument where to differentiate
* @return: double with the value of f'(x)
*/
// note there is one differentiate function !!!
// we can call it, with any argument from type double ((*f)(double),double)
double differentiate(double (*f)(double), double x) 
{
       double h = 0.0001;
       return (f(x+h)-f(x-h))/(2*h);
}

double xsquare(double x)                                // user defined function 
{
       return x*x;
}

double cube(double x)                                   // user defined function 
{
       return x*x*x;
}

int main(int argc, char *argv[])
{
    double x;
    function_pointer fcp;       // we make a variable from type function_pointer
    
    printf("differentiate the cube\n");
    fcp = cube;                                  // point to the function cube
    for(x = 0;x < 1; x+=0.1) 
    {
          printf("x=%f x*x*x=%f, 3*x*x=%f, f'= %f\n",
          x, fcp(x), 3*x*x, differentiate(fcp,x));
    }

    
    printf("\ndifferentiate the square\n");
    fcp = xsquare;                               //point to the function xsquare
    for(x = 0;x < 1; x+=0.1) 
    {
          printf("x=%f   x*x=%f,   2*x=%f, f'= %f\n",
          x, fcp(x), 2*x, differentiate(fcp,x));
    } 
    

    return EXIT_SUCCESS;
}

propeller-elf-gcc -o numdiff.elf -mlmm -Os -Wall main.c -lm

best regards,
Reinhard