union_2.c

#include <stdio.h>

int main() {
    float f = 1234.5678f;
	
	union {
		float f;
		unsigned char b[4];
	} my_f;

	my_f.f = f;

    printf("float: %f\n", my_f.f);
	printf("bytes: %.2x %.2x %.2x %.2x\n", 
		my_f.b[3], my_f.b[2], my_f.b[1], my_f.b[0]);
	
	my_f.b[3] |= 0x80; //0x80 == binary 1000 0000

	printf("float: %f\n", my_f.f); //should return negative value

    return 0;
}