#include<stdio.h>

struct animal {
	char* (*talk)();
	void (*elongate)(struct animal*);
	int length;
};

// After this typdef, we can say Animal instead of struct animal
typedef struct animal Animal;


char* squirreltalk(){
	return "squirrelish chirp";
}

void squirrelstretch(struct animal* us){
	us->length += 2;
}

char *cattalk(){
	return "meow";
}

void catstretch(Animal* us){
	us->length += 4;
	// Same as (*us).length += 4;
}

void try_out_animal(Animal *pet){
	// We do not know if pet is a squirrel or a cat!
	printf("%s\n", pet->talk());
	printf("Initial Length:  %d\n", pet->length);
	pet->elongate(pet);
	printf("Final Length:  %d\n", pet->length);
}

int main(){
	Animal squirrel;
	squirrel.talk = squirreltalk;
	squirrel.elongate = squirrelstretch;
	squirrel.length = 10;

	// Different style, same result (this only works in C)
	struct animal cat = {
		.talk = cattalk,
		.elongate = catstretch,
		.length = 15
	};

	try_out_animal(&squirrel);
	try_out_animal(&cat);
	return 0;
}