/*
 * demonstrate how a union works
 *
 * this sets up something as a string and then
 * accesses it as an integer
 *
 * Matt Bishop, ECS 36A, Fall 2019
 */
#include <stdio.h>
#include <string.h>

/*
 * union to treat a variable
 * as either an integer or an
 * array of characters
 */
union chtoint {
	int x;			/* ... as an integer */
	char a[8];		/* ... as 7 characters (+ '\0') */
};

/*
 * the string to use
 * the characters are (in hex):
 * 30, 31, 32, 33, 34, 35, 36, 37, 0
 */
char *str = "1234567";

/*
 * print the bits in an integer
 */
void prbits(unsigned int x)
{
	int i;			/* counter in a for loop */
	int bit;		/* the bit */
	int nbits = sizeof(unsigned int) * 8;	/* how many bit in an unsigned int */

	/*
	 * loop through the (computer) word, putting out 1 bit at a time
	 */
	for(i = 0; i < nbits; i++){
		/* extract ith bit */
		bit = (x>>((nbits-1)-i))&01;
		/* print it, visibly */
		printf("%c", bit+'0');
		if ((i + 1) % 8 == 0)
			putchar(' ');
	}

	/* done -- end of line to finish it up */
	putchar('\n');
}


/*
 * and now the conversion
 */
int main(void)
{
	union chtoint u;	/* u can be treated as an integer or a string */

	/*
	 * give u a string value
	 * note overflow won't occur here
	 */
	strcpy(u.a, str);
	
	/*
	 * now print it out as a string, a hexadecimal integer,
	 * and a decimal integer
	 */
	printf("%s -- 0x%x or %d\n", u.a, u.x, u.x);
	
	/*
	 * the string as bits
	 */
	prbits(u.x);

	/* bye! */
	return(0);
}