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

int main(){
	void *a_pointer;
	a_pointer = main;
	printf("a_pointer = %lx\n", a_pointer);

	int a = 721;
	a_pointer = &a;
	printf("a_pointer = %lx\n", a_pointer);
	printf("a = %d\n", a);
	// a_pointer points to an integer.  Therefore, it's type is:  int*
	*(int*)a_pointer = 563; 
	printf("a = %d\n", a);

	a_pointer = sin;
	printf("a_pointer = %lx\n", a_pointer);
	// a_pointer points to a function that returns a double and takes a double
	// Therefore, it's type is:  double(*)(double)
	// ( (type) a_pointer )(parameters)
	printf("The sin of 3.14 is %lf\n", ((double(*)(double))a_pointer)(3.14));

	double our_function(double param_name){
		return 0.0;
	}
//	int a;
//	int *a;
	// To cast:  (int*)
	
	// Another method, especially good if you have to use the casted pointer a few times
	double (*pointer_to_trig)(double) = a_pointer;
	// To cast:  (double (*)(double))
	printf("The sin of 1.57 is %lf\n", pointer_to_trig(1.57));
	pointer_to_trig = cos;
	printf("The cos of 1.57 is %lf\n", pointer_to_trig(1.57));

	double (*trig_functions[])(double) = {sin, cos, tan};
	a_pointer = trig_functions;
	// The type:  double (**)(double)
	for(int i = 0; i < 3; i++)
		printf("function %d given 1.57:  %lf\n", i, trig_functions[i](1.57));

	printf("Function 2 yields %lf\n", ( (double (**)(double)) a_pointer)[2](3.14));

	return 0;
}