#include<stdio.h>

int d(int x){
	return x+x;
}

int t(int x){
	return x*3;
}

int double_op(int number, int (*operation)(int)){
	return operation(operation(number));
}

struct operations {
	int (*doubler)(int);
	int (*tripler)(int);
};

int main(){
	struct operations ops;
	ops.doubler = d;
	ops.tripler = t;
	// tester(&ops)

	printf("16 doubled is %d\n", ops.doubler(16));

	int x = 10;
	printf("%d doubled is %d\n", x, d(x));

	int (*operation)(int) = d;
	printf("%d doubled is %d\n", x, operation(x));

	operation = t;
	printf("%d doubled is %d\n", x, operation(x));

	printf("%d double doubled is %d\n", x, double_op(x, d));
	printf("%d double tripled is %d\n", x, double_op(x, t));
	return 0;
}