/*
 * A program to demonstrate that structures are call by value in C.
 * Also shows that (char *) and array of char are not the same, of
 * course. 
 * 
 * Mark A. Sheldon
 * Olin College
 * Fall 2009
 *
 */

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

#define MAX_NAME_LEN 512

struct student {
        char name[MAX_NAME_LEN];
        int  num;
};

void print_struct (struct student data)
{
        printf("{ name = %s; num = %d }\n", data.name, data.num);
}

/* 
 *  CBV stands for Call By Value.
 */
void cbv_mutate(struct student data)
{
        data.name[0] = 'b';
        data.num     = -1;
}

/*
 * CBR stands for Call By Reference.
 */
void cbr_mutate(struct student *data)
{
        data->name[0] = 'b';
        data->num     = -1;
}

int main(int argc, char **argv)
{
        struct student s, t;
        struct {
                char *name;
                int  num;
        } u;

        strncpy(s.name, "foo", MAX_NAME_LEN);
        s.num  = 4;

        t = s;

        /* u = s;                                                       */
        /*         produces an incompatible type error at compile time  */
        /*         as does an attempt to pass u to print_struct().  So  */
        /*         char[MAX_NAME_LEN] and (char *) are not the same.    */
        /*         Draw pictures of the state of the program after the  */
        /*         next two lines.                                      */

        u.name = s.name;
        u.num  = s.num;

        print_struct(s);

        cbv_mutate(s);
        print_struct(s);

        cbr_mutate(&s);
        print_struct(s);
        print_struct(t);

        /* print_struct(u); compilation error.  see above */
        printf("{ name = %s; num = %d }\n", u.name, u.num);

        return EXIT_SUCCESS;
}