#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <assert.h>

// UNION -- using cannonical syntax (not typedef), for now.

union Number {
    int   as_int;
    float as_float;
};   // Do not forget the semicolon at the end of a struct or union type definition!

void print_number(union Number n) {
    printf("n has the value %d\n", n.as_int);
}

int main(int argc, char* argv[]) {

    union Number  n = { .as_int = 3 };   // named initializer
    print_number(n);

    n.as_float = 3.1415; // This overwrites the bytes in which the int value was stored.

    print_number(n);  // BROKEN!  print_number(…) does not handle float values, yet.

    printf("sizeof(n.as_float) == %zd\n", sizeof(n.as_float));
    printf("sizeof(n.as_int)   == %zd\n", sizeof(n.as_int));
    printf("sizeof(n)          == %zd\n", sizeof(n));
    // NOTICE:  The union object occupies the same number of bytes as the large field in it.
    //          With a struct, it would be ≥ the sum of the sizes of the fields (sometimes
    //          with some padding for performance).

    // union Number  n = { .as_int = 3, .as_float = 3.1415 };   // NOT ALLOWED!
    
    return EXIT_SUCCESS;
}
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