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

// Declare a union type called 'union Number'.  The type name is 'union Number'.
union Number {
    int    as_int;
    double as_double;
};   // <<<< SEMICOLON!!! <<<<<

// UNIONS
// * Benefit of union is space and clarity.  “Say what you mean.  Mean what you say.”
// * Only one of the fields can be stored.
// * Fields share the same memory.
// * You should initialize only one of the fields in a union object.
// * You can assign a value to a different field, but that overwrites part or all of the
//   bytes used to store the field that was previously initialized or assigned to.
// * A union type provides no way to track which field has been set.

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

    printf("\nDeclare variable 'n' as 'union Number' and initialize its '.as_double'\n");
    printf("field to 654321.123456.\n");
    union Number n = { .as_double = 654321.123456 };

    printf("n.as_double == %f\n", n.as_double);
    printf("n.as_int    == %d   <<< WRONG\n", n.as_int);

    return EXIT_SUCCESS;
}
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