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

#define PI 3.141592653


double (* make_something(double multiple))(double) {
	double return_double(double x){ // This is incide make_something's stack frame!
		return multiple*x;
	}
	return return_double;
}

double (* return_tangent())(double) {
	return tan;
}

void run_on_angles(double (*tf)(double)){
	double values[] = {0, PI/2, PI, PI*1.5, 2*PI};
	for(int i = 0; i < 5; i++)
		printf("tf(%lf) = %lf\n", values[i], tf(values[i]));
}

int main(){
	double (*trig_function)(double) = sin;

	printf("tf of 3.14:  %lf\n", trig_function(3.14));
	trig_function = cos;
	printf("tf of 3.14:  %lf\n", trig_function(3.14));
	trig_function = return_tangent();
	printf("tf of 3.14:  %lf\n", trig_function(3.14));

	run_on_angles(sin);
	trig_function = make_something();
	printf("tf of 3.14:  %lf\n", trig_function(3.14));

	// Normal for C:
	// type variable_name = value;
	// function types don't follow this model!
	// return_type_of_the_function (*name_of_the_variable)(parameters_for_the_function) = value;
	double (*trig_functions[])(double) = {sin, cos, tan};
	for(int i = 0; i < 3; i++)
		run_on_angles(trig_functions[i]);

	return 0;
}