Example of undefined behavior in C

uninitialized_bool.c

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

int main(int argc, char *argv[])
{
    bool b;
    *((unsigned char *)&b) = 0xff;

    if ( b )
        printf("b is true\n");
    else
        printf("b is not true\n");

    if ( ! b )
        printf("b is false\n");
    else
        printf("b is not false\n");

    return 0;
}