example of header file in c
#ifndef SET_H
#define SET_H
#include <stdbool.h>
typedef int* Element;
typedef struct set_rec* Set;
Set SetCreate();
void SetDestroy(Set);
void SetAdd(Set, const Element);
void SetRemove(const Set, const Element);
bool SetIsIn(const Set, const Element);
bool SetIsEmpty(const Set);
const Element SetNext(Set);
const Element SetFirst(Set);
#endif