Func pointers and 'methods' in C

main.c

#include <stdio.h>

typedef struct _Opts {
    int value;
    int(*func)(int);
    int(*next_value)(struct _Opts*);
} Opts;

Opts new_opts(int value);

int main(void)
{
    char c = 0;
    printf("Is Null \\0: %d\n", c == '\0');
    Opts opts = new_opts(5);
    printf("Value: %d\n", opts.value);
    printf("Next Value: %d\n", opts.next_value(&opts));
    return 0;
}

int square(int a) {
    return a*a;
}

int next_value(Opts *opts) {
    return opts->func(opts->value);
}

Opts new_opts(int value)
{
    Opts opts;
    opts.value = value;
    opts.func = square;
    opts.next_value = next_value;
    return opts;
}