Question

How to make a nice function pointer: Start with a regular function declaration func, for example, here func is a function that takes a pair of ints and returns an int

int func(int, int);

To turn it to a function pointer, just add a * and wrap the funtion name in parenthesis like so

int (*func)(int, int);

Now func is a pointer to a funciton that takes a pair of ints and returns an int. Finally, add a typedef so that we can use func as a new type

typedef int (*func)(int, int);

which allows us to create arrays of function pointers, higher order functions etc as shown in the following example.

%%file square2.c
#include <stdio.h>
#include <math.h>

// Create a function pointer type that takes a double and returns a double
typedef double (*func)(double x);

// A higher order function that takes just such a function pointer
double apply(func f, double x)
{
    return f(x);
}

double square(double x)
{
    return x * x;
}

double cube(double x)
{
    return pow(x, 3);
}

int main()
{
    double a = 3;
    func fs[] = {square, cube, NULL};

    for (func *f=fs; *f; f++) {
        printf("%.1f\n", apply(*f, a));
    }
}

%%bash

clang -Wall -lm square2.c -o square2
./square2